The present invention relates to a method for the enzymatic production of an acyl phosphate from a 2-hydroxyaldehyde said method making use of a phosphoketolase or of a sulfoacetaldehyde acetyltransf erase, as well as to the use of a phosphoketolase or of a sulfoacetaldehyde acetyltransferase or of a microorganism expressing a phosphoketolase or a sulfoacetaldehyde acetyltransferase for the production of an acyl phosphate from a 2-hydroxyaldehyde.

For the past several decades, practitioners of metabolic engineering have endeavoured to explore biological solutions for the production of chemicals, thus, providing alternatives to more traditional chemical processes. In general, biological solutions allow for the utilization of renewable feedstocks (e.g. sugars) and compete with existing petrochemical based processes. A multi-step, biological solution for the production of a chemical typically comprises a microorganism as the catalyst for the conversion of feedstock to a target molecule. A complete set of enzyme reactions for the production of a particular target molecule can be grouped into those belonging to central carbon pathways and those belonging to the product specific pathway. The reactions belonging to central carbon and product specific pathways are linked in that redox (typically, NAD(P)H) and energetic (typically, ATP) constraints of every enzyme reaction must be accounted for in an overall balance contributing to the competitiveness of the process. Historically, central carbon pathways of heterotrophs growing on sugars have been described as the Embden-Meyerhoff-Pamas pathway (EMPP; i.e., "glycolysis"), the pentose phosphate pathway (PPP), the Entner- Doudoroff pathway (EDP), and the phosphoketolase pathway (PKP) (see Gottschalk (1986), Bacterial Metabolism, 2 ^nd Edition, Springer-Verlag, New York). Each central pathway or combinations of central pathways offer advantages and disadvantages with respect to a specific target molecule. In order to provide competitive bioprocesses, recombinant microorganisms with modifications involving the EMPP, PPP and EDP have been described (M. Emmerling et al., Metab. Eng. 1 :117 (1999); L. O. Ingram et al., Appl. Environ. Microbiol. 53: 2420 (1987); C. T. Trinh et al., Appl. Environ. Microbiol. 74:3634 (2008)). More recently, recombinant microorganisms with modifications involving the PKP have been described (see Sonderegger et al. Appl. Environ. Microbiol. 70 (2004), 2892-2897, US Patent 7,253,001 , Chinen et al. J. Biosci. Bioeng. 103 (2007), 262-269, US Patent 7,785,858; Fleige et al., Appl. Microbiol. Cell Physiol. 91 (2011 ), 769-776).

The EMPP (glycolysis) converts 1 mol glucose to 2 mol pyruvate (PYR). When acetyl-CoA is desired, 1 mol PYR can be converted to 1 mol of acetyl-CoA (AcCoA) with the concomitant generation of 1 mol C0 ₂ and 1 mol NADH. The sum of the reactions is given in Equation 1. glucose + 2 ADP + 2 H ₃ P0 ₄ + 2 CoA + 4 NAD ⁺ - ^■ »

2 acetyl-CoA + 2 C0 ₂ + 2 ATP + 2 H ₂ 0 + 4 NADH + 4 H ⁺

(Equation 1 )

The PPP provides a means to convert 1 mol glucose to 1 mol C0 ₂ and 2 mol NADPH, with the concomitant generation of 0.67 mol fructose-6-phosphate (F6P) and 0.33 mol glyceraldehyde-3-phosphate (GAP). The F6P and GAP thus formed must be metabolized by other reaction pathways, e.g. by the EMPP. The EDP converts 1 mol glucose to 1 mol GAP and 1 mol PYR with the concomitant generation of 1 mol NADPH. As with the PPP, the GAP thus formed must be metabolized by other reaction pathways. The PKP provides a means to convert 1 mol glucose to 1 mol GAP and 1.5 mol acetyl phosphate (AcP). When acetyl-CoA is desired, 1 equivalent of AcP plus 1 equivalent coenzyme A (CoA) can be converted to 1 equivalent acetyl-CoA and 1 equivalent inorganic phosphate (Pi) by the action of phosphotransacetylase.

In view of the increasing demand for processes which make use of renewable resources for producing all sorts of compounds, it is desirable to provide means and methods which allow for an efficient production of central metabolites, such as acyl- CoA or carboxylic acids, or their precursors, thereby building a platform for developing further processes to convert these metabolites into useful compounds.

Thus, there is a need to provide methods, comprising central carbon and product specific pathways, that maximize the conversion of feedstock to product by best accommodating the redox and energetic constraints of enzyme reactions, thereby allowing the energetically efficient production of precursors of acyl-CoA or carboxylic acid, in particular of microorganisms which can be used for the production of numerous industrially important compounds from renewable resources, such as organic acids, alkenes, dienes or short chain carboxylic acids. Applicants have addressed this need by providing the embodiments as defined in the claims.

Thus, the present invention relates to method for the enzymatic production of an acyl phosphate from a 2-hydroxyaldehyde and phosphate in which the production of an acyl phosphate from a 2-hydroxyaldehyde and phosphate is achieved by the use of a phosphoketolase or of a sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) according to the following reaction scheme:

2-hydroxyaldehyde acyl phosphate wherein R and R ² are selected independently from H, CH ₃ , CH ₂ OH and C ₂ H ₅ and wherein if R ¹ is H, R ² cannot be H.

The term "wherein if R ¹ is H, R ² cannot be H" as used in the context of the present invention means that R ¹ and R ² cannot be H at the same time, i.e. it also means that if R ² is H, R ¹ cannot be H.

The present application describes that enzymes which are classified as phosphoketolases or as sulfoacetaldehyde acetyltransferases (EC 2.3.3.15) are capable of catalyzing the formation of an acyl phosphate from a 2-hydroxyaldehyde as defined above and phosphate.

Different types of phosphoketolases are known and all of them can be employed in the method according to the invention. Generally, phosphoketolases are classified into two types based on substrate preference as regards their naturally catalyzed reaction: xylulose-5-phosphate (X5P) phosphoketolases, which are classified in EC 4.1.2.9 and which naturally use X5P and fructose-6-phosphate (F6P) as a substrate but which prefer X5P, and X5P/fructose-6-phosphate (F6P) phosphoketolases, which are classified in 4.1.2.22 and which can use both X5P and F6P with comparable activities as substrate (Suzuki et al., J. Biol. Chem. 44 (2010), 34279-34287). In the following, the term "phosphoketolase" always refers to both types.

Thus, X5P phosphoketolases are enzymes which are classified in EC 4.1.2.9 and which are capable of catalyzing the following reaction:

D-xylulose-5-phosphate + phosphate → D-glyceraldehyde-3-phosphate + acetyl- phosphate + H ₂ 0

The other type of phosphoketolases which are classified in EC 4.1.2.22 are generally referred to as fructose-6-phosphate phosphoketolases and are naturally capable of catalyzing the following reaction:

D-Fructose-6-phosphate + phosphate → acetyl phosphate + D-erythrose 4- phosphate + H ₂ 0

There are also cases in which a phosphoketolase is assigned to both types of phosphoketolases, e.g., in the case of the phosphoketolase from Nitrolancetus hollandicus Lb, or where an identified phosphoketolase has not yet been assigned to any of the two types but is simply generally classified as a phosphoketolases. The term "phosphoketolase" when used herein also refers to all these phosphoketolases.

Thus, in one embodiment of the method according to the present invention the enzymatic conversion of a 2-hydroxyaldehyde and phosphate into an acyl phosphate according to the above shown reaction scheme is achieved by making use of a phosphoketolase which is classified as a phosphoketolases in EC 4.1.2.9. This enzyme has been identified in a variety of organisms, in particular microorganisms such as bacteria and fungi. In one preferred embodiment the phosphoketolase (EC 4.1.2.9) originates from a prokaryotic organism, preferably a bacterium. The enzyme has, for example, been described to occur in Lactococcus lactis, Lactobacillus plantarum (Uniprot Accession numbers: Q88S87; Q88U67), Lactobacillus pentosus (Uniprot Accession number: Q937F6), Lactobacillus reuteri, Bifidobacterium animalis (Uniprot Accession number: A0PAD9), Bifidobacterium animalis subsp. lactis (Uniprot Accession number: Q9AEM9), Butyrovibrio fibrisolvens, Fibrobacter intestinalis, Fibrobacter succinogenes, Leuconostoc mesenteroides, Oenococcus oeni, Starkeya novella, Thiobacillus sp., Thermobispora bispora (strain ATCC 19993 / DSM 43833 / CBS 139.67 / JCM 10125 / NBRC 14880 / R51 ; Uniprot Accession number D6YAD9), Thermobaculum terrenum (strain ATCC BAA-798 / YNP1 ; Uniprot Accession number D1CI63) and Nitrolancetus hollandicus Lb (Uniprot Accession number I4EJ52).

In another preferred embodiment the phosphoketoiase (EC 4.1.2.9) originates from a eukaryotic organism, preferably a fungus, e.g. a yeast, such as S. cerevisiae. The enzyme has, for example, been described to occur in Emericella nidulans (Uniprot Accession number: Q5B3G7), Metarhizium anisopliae (Uniprot Accession number: C1 K2N2), Candida boidinii, Candida curvata, Candida famata, Candida humicola, Candida parapsilosis, Candida parapsilosis NCYC 926, Candida tropicalis, Cyberlindnera jadinii, Cyberlindnera saturnus, Debaromyces robertsiae, Fusarium oxysporum, Kluyveromyces marxianus, Kluyveromyces phaseolosporus, Lipomyces starkeyi, Ogataea angusta, Pachysolen tannophilus, Priceomyces medius, Saccharomyces cerevisiae, Rhodospiridium toruloides, Rhodotorula glutinis, Rhodotorula graminis, Penicillium chrysogenum, Trichosporon cutaneum and Yarrowia lipolytica.

The enzymatic activity of a phosphoketoiase (EC 4.1.2.9) can be assessed with methods known to a person skilled in the art. Such methods are, e.g., described in Meile et al. (J. Bacteriol. 183 (2001), 2929-2936) and in Suzuki et al (Acta Cryst. F66 (2010), 941-943)..

The phosphoketoiase (EC 4.1.2.9) is structurally and functionally well defined. For example, Petrareanu et al. (Acta Crystallographica F66 (2010), 805-807) describe the X-ray crystallographic analysis of the xylulose-5-phosphate phosphoketoiase from Lactococcus lactis.

In another embodiment of the method according to the present invention the enzymatic conversion of a 2-hydroxyaldehyde and phosphate into an acyl phosphate according to the above shown reaction scheme is achieved by making use of a phosphoketoiase which is classified as a fructose-6-phosphate phosphoketoiase in EC 4.1.2.22. This enzyme has been identified in a variety of organisms, in particular microorganisms such as bacteria and fungi. In one preferred embodiment the fructose-6-phosphate phosphoketoiase (EC 4.1.2.22) originates from a prokaryotic organism, preferably a bacterium. The enzyme has, for example, been described to occur in Bifidobacterium adolescentis, Bifidobacterium animalis subsp. lactis (Uniprot Accession number: Q9AEM9), Bifidobacterium longum, Bifidobacterium pseudolongum, in particular Bifidobacterium pseudolongum subsp. globosum, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium dentium, Bifidobacterium mongoliense, Bifidobacterium bombi, Cupriavidus necator, Gardnerella vaginalis, Gluconacetobacter xylinus, Lactococcus crispatus, Lactobacillus paraplantarum, Leuconostoc mesenteroides and Nitrolancetus hollandicus Lb (Uniprot Accession number I4EJ52).

In another preferred embodiment the fructose-6-phosphate phosphoketolase (EC 4.1.2.22) originates from a eukaryotic organism, preferably a fungus, e.g. a yeast, such as S. pastorianus. The enzyme has, for example, been described to occur in Candida sp., Candida sp. 107, Candida tropicalis, Rhodotorula glutinis, Rhodotorula graminis and Saccharomyces pastorianus.

The enzyme is structurally and functionally well defined. For example, Suzuki et al. (Acta Crystallographica F66 (2010), 941-943; J. Biol. Chem. 285 (2010), 34279- 34287) describe the overexpression, crystallization and X-ray analysis of the phosphoketolase from Bifidobacterium breve. The gene encoding the xylulose-5- phosphate/fructose-6-phosphate phosphoketolase frm Bidifobacterium lactis is e.g. described in Meile et al. (J. Bacteriol. 183 (2001), 2929-2936).

The enzymatic activity of a fructose-6-phosphate phosphoketolase (EC 4.1.2.22) can be assessed with methods known to a person skilled in the art. Such methods are, e.g., described in Meile et al. (J. Bacteriol. 183 (2001), 2929-2936) and in Suzuki et al. (Acta Cryst. F66 (2010), 941-943).

Other phosphoketolases which have not yet been classified into EC 4.2.1.9 or EC 4.2.1.22 and which can be used in the method according to the present invention are, e.g. the phosphoketolase from Thermosynechococcus elongatus (strain BP-1 ; Uniprot Accession number: Q8DJN6), the phosphoketolase from Bacillus coagulans 36D1 (Uniprot Accession number: G2TIL0), the phosphoketolase from Lactococcus lactis subsp. lactis (Strain KF 47; Uniprot Accession number. A9QST6), the phosphoketolase from Bifidobacterium pseudolongum subsp. globosum (Uniprot Accession number: Q6R2Q6) and the phosphoketolase from Clostridium acetobutylicum (Strain ATCC 824; Uniprot Accession number: Q97JE3; Servisky et al. (J. Ind. Microbiol. Biotechnol. 39 (2012), 1859-1867); SEQ ID NO: 2).

In the appended Examples it is shown that 2,3-hydroxypropanal (D, L- glyceraldehyde) and 2-hydroxypropanal (D, L-lactaldehyde) can be converted by phosphoketolase into 3-hydroxypropionyl phosphate and propionyl phosphate, respectively, which can then be further converted into 3-hydroxypropionic acid and propionic acid, respectively, by spontaneous hydrolyzation.

In one embodiment the phosphoketolase employed in a method according to the present invention is a phosphoketolase from Bifidobacterium pseudolongum subsp. globosum (Uniprot Accession number: Q6R2Q6; SEQ ID NO: 1 ) or a phosphoketolase from Clostridium acetobutylicum (Strain ATCC 824; Uniprot Accession number: Q97JE3; SEQ ID NO: 2) or a phosphoketolase from Lactococcus lactis subsp. lactis (Strain KF147; Uniprot Accession number: A9QST6; SEQ ID NO: 3) or a phosphoketolase from Lactococcus crispatus (Uniprot Accession number: D5H215; SEQ ID NO: 20) or a phosphoketolase from Bifidobacterium gallicum (DSM 20093; Uniprot Accession number: D1 NS90; SEQ ID NO: 16) or a phosphoketolase from Leuconostoc citreum (strain KM20 ; Uniprot Accession number: B1 MWV8; SEQ ID NO: 17) or a phosphoketolase from Streptococcus gordonii (strain Challis / ATCC 35105 / CH1 / DL1 / V288; Uniprot Accession number: A8AV21 ; SEQ ID NO: 18) or a phosphoketolase from Thiobacillus denitrificans (strain ATCC 25259; Uniprot Accession number: Q3SKJ7; SEQ ID NO: 19).

In a preferred embodiment, the phosphoketolase employed in the method of the invention has an amino acid sequence as shown in any one of SEQ ID NOs: 1 to 3 or 16 to 20 or shows an amino acid sequence which is at least x% homologous to any one of SEQ ID NOs: 1 to 3 or 16 to 20 and is a phosphoketolase with x being an integer between 30 and 100, preferably 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 91 , 92, 93, 94, 95, 96, 97, 98 or 99 wherein such an enzyme is capable of converting a 2-hydroxyaldehyde and phosphate into an acyl phosphate as set forth herein above. Preferably, the degree of identity is determined by comparing the respective sequence with the amino acid sequence of any one of the above-mentioned SEQ ID NOs. When the sequences which are compared do not have the same length, the degree of identity preferably either refers to the percentage of amino acid residues in the shorter sequence which are identical to amino acid residues in the longer sequence or to the percentage of amino acid residues in the longer sequence which are identical to amino acid residues in the shorter sequence. The degree of sequence identity can be determined according to methods well known in the art using preferably suitable computer algorithms such as CLUSTAL.

When using the Clustal analysis method to determine whether a particular sequence is, for instance, 80% identical to a reference sequence default settings may be used or the settings are preferably as follows: Matrix: blosum 30; Open gap penalty: 10.0; Extend gap penalty: 0.05; Delay divergent: 40; Gap separation distance: 8 for comparisons of amino acid sequences. For nucleotide sequence comparisons, the Extend gap penalty is preferably set to 5.0.

Preferably, the degree of identity is calculated over the complete length of the sequence.

It has been described that a multiple alignment of phosphoketolase sequences shows several highly conserved regions and two of these regions are used as signature patterns for phosphoketolases (http://prosite.expasy.org/PDOC60002). The first signature pattern is E-G-G-E-L-G-Y and the second signature pattern is G-x(3)- [DN]-x-P-x(2)-[LIVFT]-x(3)-[LIVM]-x-G-D-G-E. The function of the first signature pattern is not yet known while the second signature pattern corresponds to the thiamine pyrophosphate binding site. Thus, in a preferred embodiment, a phosphoketolase as defined herein above has an amino acid sequence which contains at least one of the two above mentioned signature patterns, preferably at least the second signature pattern, and even more preferably both signature patterns.

Sequence comparisons show that the overall sequence identity between phosphoketolases from different origins can be as low as around 26%. For example, Meile et al. (J. Biol. Chem. 183 (2001 ), 2929-2936) reports that the D-xylulose 5- phosphate/D-fructose 6-phosphate phosphoketolase gene (xfp) of Bifidobacterium lactis revealed identities of 26% to 55% to sequences in the genomes of other organisms.

Whether a chosen phosphoketolase is capable of catalyzing the conversion of a 2- hydroxyaldehyde and phosphate into acyl phosphate and H ₂ O can, e.g., be assessed by an assay as set forth in the appended Examples.

The term "phosphate" as used in connection with the method of the invention refers to a compound which is acceptable as a phosphate source for the enzyme employed in the method for the conversion of a 2-hydroxyaldehyde and phosphate into an acyl phosphate and H ₂ O. One possibility is the provision of phosphate in the form of phosphoric acid, i.e. H3PO ₄ . However, also other forms are conceivable, in particular salts of phosphoric acid (H ₃ PO ₄ ) in which one, two or three of the hydrogen atoms are replaced by other ions, such as sodium ions. Phosphoketolases are thiamine diphosphate-dependent enzymes, i.e. they require thiamine diphosphate (also referred to as ThDP or TPP) as a cofactor. Therefore, it is advantageous that in a method according to the invention, when a phosphoketolase is employed, TPP is provided during the reaction. Moreover, some phosphoketolases require ions, such as Mg ²⁺ or Ca ²⁺ as cofactors. In such a case, the method according to the invention also includes the presence of such ions during the conversion as described above.

The enzymatic conversion of a 2-hydroxyaldehyde and phosphate into an acyl phosphate according to the above shown reaction scheme can also be achieved by making use of a sulfoacetaldehyde acetyltransferase (EC 2.3.3.15). Sulfoacetaldehyde acetyltransferases (EC 2.3.3.15) are enzymes which can catalyze the following reaction:

2-sulfoacetaldehyde + phosphate → acetyl phosphate + sulfite

The enzyme has been identified in a variety of organisms, in particular bacteria. In one preferred embodiment the sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) originates from a prokaryotic organism, preferably a bacterium. The enzyme has, for example, been described to occur in Castellaniella defragrans (Uniprot Accession number: Q84H44; previously Alcaligenes defragans (Ruff et al., Biochem. J. 369 (2003), 275-285)), Alcaligenes xylosoxidans xylosoxidans (Uniprot Accession number: Q84H41 ), Desulfonispora thiosulfatigenes (Uniprot Accession number: Q93PS3), Rhizobium meliloti (strain 1021 ) (Uniprot Accession number: Q92UW6), Ruegeria pomeroyi (Uniprot Accession number: Q5LMK2), Cupriavidus necator (Uniprot Accession number: Q0K022), Roseovarius nubinhibens (Uniprot Accession number: A3SR25), Acinetobacter sp. and Pseudomonas aeruginosa.

In principle any sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) can be employed in the conversion of a 2-hydroxyaldehyde and phosphate into an acyl phosphate according to a method of the invention.

Sulfoacetaldehyde acetyltransferases are, like phosphoketolases, thiamine pyrophosphate (TPP)-dependent enzymes and therefore are characterized in that they contain a TPP binding domain. Among the sulfoacetaldehyde acetyltransferases known, the TPP binding domain is highly conserved (see, e.g., Ruff et al., Biochem. J. 369 (2003), 275-285). Overall, the known sulfoacetaldehyde acetyltransferases show a high degree of sequence conservation near the N-terminus, including the TPP binding domain (see Ruff et al., loc. cit). Sequence divergence can be observed in the N-terminus of the enzymes itself and in a region near amino acid 400 of the C. defragrans enzyme. Ruff et al. (loc. cit.) describe that sulfoacetaldehyde acetyltransferases form 3 subgroups (see Figure 4 of said publication). Subgroups 2 and 3 are said to show a TPP binding domain conforming with the PROSITE consensus sequence

(L/l/V/M/F)(G/S/A)X ₅ PX ₄ (L/IA//M/FA'AA/)X(L/l V/lvl/F)XGD(G/S/A)(G/S/A/C), while subgroup slightly deviates from the consensus sequence:

(L/l/V/M/F)(G/S/A)X ₅ PX ₄ (L/I M/F/Y/W)X(L/l/V/M/FA ^r )XGD(G/S/A)(G/S/A/C).

Apart from these regions, the sequence identity between the different sulfoacetaldehyde acetyltransferases can be rather low (down to about 44%).

In a preferred embodiment, the sulfoacetaldehyde acetyltransferase employed in a method according to the present invention is the sulfoacetaldehyde acetyltransferase of C. defragrans showing the amino acid sequence as depicted in SEQ ID NO:4 or the sulfoacetaldehyde acetyltransferase of Alcaligenes xylosoxidans xylosoxidans showing the amino acid sequence as depicted in SEQ ID NO:5 or the sulfoacetaldehyde acetyltransferase of Desulfonispora thiosulfatigenes showing the amino acid sequence as depicted in SEQ ID NO:6 or the sulfoacetaldehyde acetyltransferase of Rhizobium meliloti (strain 1021 ) showing the amino acid sequence as depicted in SEQ ID NO:7 or the sulfoacetaldehyde acetyltransferase of Roseovarius nubinhibens showing the amino acid sequence as depicted in SEQ ID NO:8 or showing a related amino acid sequence.

Thus, in a preferred embodiment, the sulfoacetaldehyde acetyltransferase employed in the method of the invention has an amino acid sequence as shown in any one of SEQ ID NOs: 4 to 8 or shows an amino acid sequence which is at least x% homologous to any one of SEQ ID NOs: 4 to 8 and is a sulfoacetaldehyde acetyltransferase with x being an integer between 30 and 100, preferably 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 91 , 92, 93, 94, 95, 96, 97, 98 or 99 wherein such an enzyme is capable of converting a 2-hydroxyaldehyde and phosphate into an acyl phosphate as set forth herein above. Preferably, the degree of identity is determined as described above.

The enzymatic activity of a sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) can be assessed with methods known to a person skilled in the art. Such methods are, e.g., described in Ruff et al. (Biochem. J. 369 (2003), 275-285).

In the appended Examples it is shown that D, L-lactaldehyde (racemic 2- hydroxypropanal) and D, L-glyceraldehyde (racemic 2,3-hydroxypropanal) can be converted by sulfoacetaldehyde acetyltransferases into propionyl phosphate and 3- hydroxypropionyl phosphate, respectively, which can then be further converted into propionic acid and 3-hydroxypropionic acid, respectively, by spontaneous hydro lyzation.

In a preferred embodiment, the 2-hydroxyaldehyde of the following formula

2-hydroxyaldehyde wherein R ¹ and R ² are selected independently from H, CH ₃ , CH ₂ OH and C2H5 and wherein if R ¹ is H, R ² cannot be H, which is converted into an acyl phosphate according to a method of the present invention, is 2-hydroxypropanal (lactaldehyde) which is converted into propionyl phosphate. Thus, in a preferred embodiment, the present invention relates to a method for the enzymatic production of propionyl phosphate from 2-hydroxypropanal (lactaldehyde) by making use of a phosphoketolase or of a sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) wherein the conversion of 2-hydroxypropanal (lactaldehyde) into propionyl phosphate occurs according to the following reaction scheme:

H3PO4

2-hydroxypropanal propionyl phosphate

In another preferred embodiment, the 2-hydroxyaldehyde of the following formula

2-hydroxyaldehyde wherein R ¹ and R ² are selected independently from H, CH _3> CH ₂ OH and C ₂ H5 and wherein if R ¹ is H, R ² cannot be H, which is converted into an acyl phosphate according to a method of the present invention, is 2,3-dihydroxypropanal (glyceraldehyde) which is converted into 3-hydroxypropionyl phosphate. Thus, in a preferred embodiment, the present invention relates to a method for the enzymatic production of 3-hydroxypropionyl phosphate from 2,3-dihydroxypropanal (glyceraldehyde) by making use of a phosphoketolase or of a sulfoacetaldehyde acetyltransferase (EC 2.3.3.15) wherein the conversion of 2,3-dihydroxypropanal (glyceraldehyde) into 3-hydroxypropionyl phosphate occurs according to the following reaction scheme:

2,3-dihydroxypropanal 3-hydroxypropionyl phosphate

The acyl phosphate produced according to a method of the present invention can be further converted into desired molecules such as a carboxyiic acid or a corresponding acyl-Coenzyme A (also referred to as acyl-CoA).

The conversion of an acyl phosphate into the corresponding carboxyiic acid can occur via hydrolysis which functions according to the following reaction scheme:

acyl phosphate carboxyiic acid wherein R ¹ and R ² are selected independently from H, CH ₃ , CH ₂ OH and C2H5 and wherein if R ¹ is H, R ² cannot be H.

The hydrolysis of an acyl phosphate as defined herein above into a corresponding carboxylic acid in vitro can occur spontaneously since acyl phosphates are rather unstable.

It is also possible to achieve the conversion by an enzymatically catalyzed reaction. The enzymatic hydrolysis of an acyl phosphate into the corresponding carboxylic acid and H ₃ P0 ₄ can, for example, be achieved by making use of an acylphosphatase (EC 3.6.1.7). Acylphosphatase (AcP; EC 3.6.1.7) is a cytosolic enzyme (with a molecular weight of about 10 kDa) widely expressed in eukaryotic and prokaryotic organisms (both mesophilic and extremophilic). AcP can be found in many tissues of vertebrate species in the skeletal muscles and in the heart as muscle-type AcP (MT-AcP) and in erythrocytes, brain and testis as (organ) common-type AcP (CT-AcP) (Zuccotti et al., Acta Cryst. 61 (2005), 144-146). Acylphosphatases catalyze the following reaction:

Acyl phosphate + H ₂ 0 - carboxylic acid + H ₃ P0 ₄

This enzyme has been described in a large variety of organisms. Preferably, an acylphosphatase employed in a method according to the present invention is derived from Gallus gallus, Cavia porcellus (Liguri et al., Biochem. J. 217 (1984), 499-505), Homo sapiens, Sus scrofa, Bos taurus, Oryctolagus cuniculus, Equus acallus or Pyrococcus hirokoshii (Miyazoo et al., Acta Crystallographica D60 (2004), 1135- 1136).

The structural and functional characteristics of these enzymes have already been studied in detail and are described, e.g., in Liguri et al. (Biochem. J. 217 (1984), 499- 505), Miyazoo et al. (Acta Crystallographica D60 (2004), 1135-1136) and in Taddei et al. (FEBS Letters 362 (1995), 175-179).

Alternatively, it can occur by an enzymatic reaction which involves the generation of ATP from ADP according to the following reaction scheme:

ADP

acyl phosphate carboxylic acid

In particular, an acyl phosphate can also be converted, in vitro or in vivo, enzymatically into a corresponding carboxylic acid, e.g. by making use of an enzyme which is classified as EC 2.7.2.-, i.e., a phosphotransferase. Such enzymes use a carboxyl group as acceptor. Thus, the conversion of an acyl phosphate into the corresponding carboxylic acid can, e.g., be achieved by making use of an enzyme with a carboxy group as acceptor (EC 2.7.2.-). Examples of such enzymes are enzymes which are classified as an acetate kinase (EC 2.7.2.1 ), as a butyrate kinase (EC 2.7.2.7), as an acetate kinase (diphosphate) (EC 2.7.2.12), as a branched-chain- fatty-acid kinase (EC 2.7.2.14) or as a propionate kinase (EC 2.7.2.15).

Acetate kinase (EC 2.7.2.1 ) is an enzyme which catalyzes the following reaction:

ATP + acetate ADP + acetyl phosphate.

Since this reaction is reversible, the enzyme can be employed to convert an acyl phosphate into the corresponding carboxylic acid. The reaction may be pushed into the direction of the carboxylic acid by continuously removing ATP from the reaction, e.g. by further enzymatic conversion or by removal from the reaction by means and methods known to the person skilled in the art. This enzyme occurs in a large variety of organisms, in particular in prokaryotes, eukaryotes and archae. It is an important enzyme in glycolysis and the enzyme levels are normally increased in the presence of excess glucose. This enzyme has, e.g., been described to occur in a number of organisms, in particular bacteria and eukaryotes. In one preferred embodiment the enzyme is from a bacterium, preferably from a bacterium of the genus Methanosarcina, Cryptococcus, Ethanoligenens, Propionibacterium, Roseovarius, Streptococcus, Salmonella, Acholeplasma, Acinetobacter, Ajellomyces, Bacillus, Borrelia, Chaetomium, Clostridium, Coccidioides, Coprinopsis, Cryptococcus, Cupriavidus, Desulfovibrio, Enterococcus, Escherichia, Ethanoligenes, Geobacillus, Helicobacter, Lactobacillus, Lactococcus, Listeria, Mesoplasma, Moorella, Mycoplasma, Oceanobacillus, Propionibacterium, Rhodospeudomonas, Roseovarius, Salmonella, Staphylococcus, Thermotoga or Veillonella, more preferably from a bacterium of the species Methanosarcina thermophila, Cryptococcus neoformans, Ethanoligenens harbinense, Propionibacterium acidipropionici, Streptococcus pneumoniae, Streptococcus enterica, Streptococcus pyogenes, Acholeplasma laidlawii, Acinetobacter calcoaceticus, Ajellomyces capsulatus, Bacillus subtilis, Borrelia burgdorferi, Chaetomium globosum, Clostridium acetobutylicum, Clostridium thermocellum, Coccidioides immitis, Coprinopsis cinerea, Cryptococcus neoformans, Cupriavidus necator, Desulfovibrio vulgaris, Enterococcus faecalis, Escherichia coli, Ethanoligenes harbinense, Geobacillus stearothermophilus, Helicobacter pylori, Lactobacillus delbrueckii, Lactobacillus acidophilus, Lactobacillus sanfranciscensis, Lactococcus lactis, Listeria monocytogenes, Mesoplasma florum, Methanosarcina acetivorans, Methanosarcina mazei, Moorella thermoacetica, Mycoplasma pneumoniae, Oceanobacillus iheyensis, Propionibacterium freudenreichii, Propionibacterium acidipropionici, Rhodospeudomonas palustris, Salmonella enteric, Staphylococcus aureus, Thermotoga maritime or Veillonella parvula.

In another preferred embodiment the enzyme is an enzyme from a fungus, preferably from a fungus of the genus Aspergillus, Gibberella, Hypocrea, Magnaporthe, Phaeosphaeria, Phanerochaete, Phytophthora, Sclerotinia, Uncinocarpus, Ustilago or Neurospora even more preferably from a fungus of the species Aspergillus fumigates, Aspergillus nidulans, Gibberella zeae, Hypocrea jecorina, Magnaporthe grisea, Phaeosphaeria nodorum, Phanerochaete chrysosporium, Phytophthora ramorum, Phytophthora sojae, Sclerotinia sclerotiorum, Uncinocarpus reesii, Ustilago maydis or Neurospora crassa.

In a further preferred embodiment the enzyme is an enzyme from a plant or an algae, preferably from the genus Chlamydomonas, even more preferably from the species Chlamydomonas reinhardtii.

In another embodiment the enzyme is from an organism of the genus Entamoeba, more preferably of the species Entamoeba histolytica.

In principle any acetate kinase (EC 2.7.2.1 ) can be used which is able to convert an acyl phosphate into the corresponding carboxylic acid in a method according to the invention.

The conversion of an acyl phosphate into the corresponding carboxylic acid can also be achieved by making use of a butyrate kinase (EC 2.7.2.7). Butyrate kinases are enzymes which catalyze the following reaction:

ATP + butanoate IT ^" " ADP + butanoyl phosphate It has been described, e.g. by Hartmanis (J. Biol. Chem. 262 (1987), 617-621) that butyrate kinase can use a number of substrates in addition to butyrate, e.g. valerate, isobutyrate, isovalerate and vinyl acetate. The enzyme has been described in a variety of organisms, in particular bacteria. In one preferred embodiment the enzyme is from a bacterium, preferably from a bacterium of the genus Lactobacillus, Geobacillus, Clostridium, Butyrivibrio, Thermotoga or Enterococcus. Preferred is Clostridium, Lactobacillus or Geobacillus. More preferably the enzyme is from a bacterium of the species Clostridium acetobutylicum, Clostridium proteoclasticum, Clostridium tyrobutyricum, Clostridium butyricum, Clostridium pasteurianum, Clostridium tetanomorphum, Butyrivibrio firbrosolvens, Butyrivibrio hungatei, Thermotoga maritime or Enterococcus durans. Preferred is Clostridium acetobutylicum. For this organism two butyrate kinases have been described: butyrate kinase 1 (Uniprot Accession number: Q45829) and butyrate kinase II (Uniprot Accession number: Q97ll19).ln another preferred embodiment the butyrate kinase is a butyrate kinase from Lactobacillus casei, e.g. Lactobacillus casei W56 (Uniprot Accession number: K0N529) or from Geobacillus sp., e.g. Geobacillus sp. GHH01 (Uniprot Accession number: L8A0E1 ). The amino acid sequences of said proteins are shown in SEQ ID NO: 13 and 14, respectively.

It is, of course, not only possible to use an enzyme exactly showing the amino acid of SEQ ID NO: 13 or 14. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 13 or 14. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91%, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO: 13 or 14 and the enzyme has the enzymatic activity of converting an acyl phosphate as defined herein above into the corresponding carboxylic acid. As regards the determination of the sequence identity, the same applies as has been set forth above.

Moreover, the conversion of an acyl phosphate into the corresponding carboxylic acid can also be achieved by making use of an acetate kinase (diphosphate) (EC 2.7.2.12). Acetate kinases (diphosphate) (EC 2.7.2.12) are enzymes which naturally catalyze the following reaction:

Diphosphate + acetate H ₃ PO ₄ + acetyl phosphate.

This enzyme has been described to occur in Entamoeba histolytica. Moreover, the conversion of an acyl phosphate into the corresponding carboxylic acid can also be achieved by making use of a branched-chain-fatty-acid kinase (EC 2.7.2.14). Branched-chain-fatty-acid kinases (EC 2.7.2.14) naturally catalyze the following reaction:

Alkyl carboxylic acid + ATP acyl phosphate + ADP

wherein "alkyl" may be 2-methylbutanoate, butanoate, isobutanoate, pentanoate or propionate. The latter reaction with propionate has been described for a branched- chain fatty acid kinase from a spirochaete (J. Bacteriol. 152 (1982), 246-54).

This enzyme has been described to occur in a number of bacteria. Thus, in one preferred embodiment the enzyme is an enzyme from a bacterium, preferably of the genus Spirochaeta or Thermotoga, more preferably Thermotoga maritime.

Also a propionate kinase (EC 2.7.2.15) can be used for the conversion of an acyl phosphate as defined herein above into the corresponding carboxylic acid. Propionate kinases (EC 2.7.2.15) naturally catalyze the following reactions:

Propanoate + ATP ,^ ^"* *^ propanoyl phosphate + ADP

Acetate + ATP acetyl phosphate + ADP

This enzyme has been described to occur in a number of bacteria, in particular Enterobacteriacea. Thus, in one preferred embodiment the enzyme is an enzyme from a bacterium, preferably of the genus Salmonella or Escherichia, more preferably of the species Salmonella enterica, Salmonella typhimurium or Escherichia coli.

In a preferred embodiment, the conversion of an acyl phosphate as defined herein above into the corresponding carboxylic acid is achieved by making use of a propionate kinase from Salmonella typhimurium, preferably from Salmonella typhimurium strain ATCC 700720. The amino acid sequence of said protein is shown in SEQ ID NO: 9.

It is, of course, not only possible to use an enzyme exactly showing this amino acid of SEQ ID NO: 9. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 9. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91%, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO:9 and the enzyme has the enzymatic activity of converting an acyl phosphate as defined herein above into the corresponding carboxylic acid. As regards the determination of the sequence identity, the same applies as has been set forth above.

In another preferred embodiment, the conversion of an acyl phosphate as defined herein above into the corresponding carboxylic acid is achieved by making use of a propionate kinase from Escherichia coli, preferably from Escherichia coli strain K12. The amino acid sequence of said protein is shown in SEQ ID NO: 10.

It is, of course, not only possible to use an enzyme exactly showing the amino acid of SEQ ID NO: 10. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 10. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91 %, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO: 10 and the enzyme has the enzymatic activity of converting an acyl phosphate as defined herein above into the corresponding carboxylic acid. As regards the determination of the sequence identity, the same applies as has been set forth above.

As is evident from the PROSITE database (http://prosite.expasy.org/cgi- bin/prosite/prosite-search-ac?PDOC00826#ref1 ), acetate kinases, butyrate kinases and propionate kinases are evolutionary related.

There are two signature patterns for these enzymes; the first one is located in the N- terminal section and the second in the central section. Both of them are glycine-rich and are suspected to be involved in substrate or ATP-binding.

The first consensus pattern (signature 1 ) is:

[LIVMFANT]-[LIV ]-x-[LIVMA]-N-x-G-S-[ST](2)-x-[KE]

The reference for this signature in PROSITE DATABASE is PS01075

The second consensus pattern (signature 2) is:

[LIVMFATQ]-[LIVMA]-x(2)-H-x-G-x-[GT]-x-[ST]-[LIVMA]-x-[TAVC] -x(3)-G

The reference for this signature in PROSITE DATABASE is PS01076

As described above, in a preferred embodiment, the 2-hydroxyaldehyde which is converted in a method according to the present invention is 2-hydroxypropanal and it is converted into propionyl phosphate. In a preferred embodiment the propionyl phosphate is further converted into the corresponding carboxylic acid, i.e. propanoic acid, as described herein above. The corresponding reaction can, e.g., occur according to one of the following reaction schemes: propionyl phosphate propionic acid

ADP

propionyl phosphate propionic acid

The conversion of propionyl phosphate into propanoic acid is preferably achieved by making use of a propionate kinase (EC 2.7.2.15) as described above.

Propanoic acid (also referred to as propionic acid) is of commercial interest because it can be employed in a number of technical fields. It is primarily manufactured for use as a preservative and anti-mold agent in animal feed and grain. It is also used as a preservative and flavouring agent in packaged foods such as baked goods and cheese. For example, calcium propionate and sodium propionate, the salt forms of propanoic acid, are used in bread and tortillas to prevent mold. Furthermore, propanoic acid is used as a chemical building block for the production of herbicides, pharmaceuticals, dyes, textile and rubber products, plastics, plasticizers, cosmetics and perfumes.

Moreover, as described above, in a preferred embodiment, the 2-hydroxyaldehyde which is converted in a method according to the present invention is 2,3- dihydroxypropanal and it is converted into 3-hydroxypropionyl phosphate. In a preferred embodiment the 3-hydroxypropionyl phosphate is further converted into the corresponding carboxylic acid, i.e. 3-hydroxypropanoic acid, as described herein above. The corresponding reaction may occur, e.g., according to one of the following reaction schemes:

3-hydroxypropionyI phosphate 3-hydroxypropionic acid

ADP

3-hydroxypropionyl phosphate 3-hydroxypropionic acid

The conversion of propionyl phosphate into propanoic acid is preferably achieved by making use of a propionate kinase (EC 2.7.2.7) as described above. Preferred are enzymes from Lactobacillus casei W56 (Uniprot Accession number: K0N529) or from Geobacillus sp., e.g. Geobacillus sp. GHH01 (Uniprot Accession number: L8A0E1 ). The amino acid sequences of said proteins are shown in SEQ ID NO: 13 and 14, respectively.

It is, of course, not only possible to use an enzyme exactly showing the amino acid of SEQ ID NO: 13 or 14. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 13 or 14. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91%, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO: 13 or 14 and the enzyme has the enzymatic activity of converting propionyl phosphate or 3- hydroxypropionyl phosphate above into propanoic acid or 3-hydroxypropionic acid. As regards the determination of the sequence identity, the same applies as has been set forth above.

3-hydroxypropanoic acid (also referred to as 3-hydroxypropionic acid; 3-HP), as propanoic acid, is also of commercial relevance. It is a platform chemical which can be converted into acrylic acid, 1 ,3-propanediol, malonic acid, biodegradable polyesters and other valuable chemicals. Acrylic acid-derived products include superabsorbent polymers used in baby diapers and incontinence products, plastics, coatings, adhesives, elastomers and paints. Currently, acrylic acid is primarily made by catalytic oxidation of propene. The possibility to provide the precursor 3-HP from glucose or other renewable resources would provide a biosustainable alternative to acrylic acid production from fossil resources.

As mentioned above, the acyl phosphate produced by a method of the present invention can also be further converted into a corresponding acyl-Coenzyme A (acyl- CoA). Such a conversion occurs via the following reaction scheme:

acyl phosphate acyl-CoA wherein R ¹ and R ² are selected independently from H, CH _3l CH ₂ OH and C ₂ H ₅ and wherein if R ¹ is H, R ² cannot be H.

The conversion of an acyl phosphate into a corresponding acyl-CoA (in vitro or in vivo) can be achieved enzymatically, e.g. by the use of a phosphate acetyltransferase (EC 2.3.1.8) or by the use of a phosphate butyryltransferase (EC 2.3.1.19).

Phosphate acetyltransferases (EC 2.3.1.8) naturally catalyze the following reaction: acetyl-CoA + Η ₃ Ρ0 ₄ ^-*"" CoA + acetyl phosphate It has been described by Veit et al. (J. Biotechnol.140 (2009), 75-83) that phosphate acetyltransferase can also use as a substrate butyryl-CoA or propionyl-CoA.

The accession numbers for this enzyme family in InterPro database are IPR012147 and IPR002505, "http://www.ebi.ac.uk/interpro/entry/IPR002505"

(http://www.ebi.ac.uk/interpro/entry/lPR012147

http://www.ebi.ac.uk/interpro/entry/IPR002505)

See also http://pfam.sanger.ac.uk/family/PF01515

The enzyme has been described in a variety of organisms, in particular bacteria and fungi. Thus, in one preferred embodiment the enzyme is an enzyme from a bacterium, preferably of the genus Escherichia, Chlorogonium, Clostridium, Veillonella, Methanosarcina, Corynebacterium, Ruegeria, Salmonella, Azotobacter, Bradorhizobium, Lactobacillus, Moorella, Rhodopseudomonas, Sinorhizobium, Streptococcus, Thermotoga or Bacillus, more preferably of the species Escherichia coli, Chlorogonium elongatum, Clostridium kluyveri, Clostridium acetobutylicum, Clostridium acidurici, Veillonella parvula, Methanosarcina thermophila, Corynebacterium glutamicum, Ruegeria pomeroyi, Salmonella enterica, Azotobacter vinelandii, Bradyrhizobium japonicum, Lactobacillus fermentum, Lactobacillus sanfranciscensis, Moorella thermoacetica, Rhodopseudomonas palustris, Sinorhizobium meliloti, Streptococcus pyogenes, Thermotoga maritima or Bacillus subtilis. In another preferred embodiment the enzyme is an enzyme from a fungus, preferably from the genus Saccharomyces, more preferably of the species Saccharomyces cerevisiae.

In a preferred embodiment, the conversion of acyl phosphate into acyl-CoA is achieved by making use a phosphate acetyltransferase from Corynebacterium glutamicum, preferably from Corynebacterium glutamicum strain ATCC 13032. The amino acid sequence of said protein is shown in SEQ ID NO: 11.

It is, of course, not only possible to use an enzyme exactly showing the amino acid of SEQ ID NO: 11. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 11. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91 %, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO: 11 and the enzyme has the enzymatic activity of converting acyl phosphate into acyl-CoA. As regards the determination of the sequence identity, the same applies as has been set forth above. As mentioned above, the conversion of an acyl phosphate into a corresponding acyl- CoA (in vitro or in vivo) can also be achieved by making use of a phosphate butyryltransferase (EC 2.3.1.19).

Phosphate butyryltransferases (EC 2.3.1.19) naturally catalyze the following reaction Butyryl-CoA + H ₃ PO ₄ butyryl phosphate + CoA

It has been described by Wiesenborn et al. (Appl. Environ. Microbiol. 55 (1989), 317- 322) and by Ward et al. (J. Bacteriol. 181 (1999), 5433-5442) that phosphate butyryltransferases (EC 2.3.1.19) can use a number of substrates in addition to butyryl coenzyme A (butyryl-CoA), in particular acetyl-CoA, propionyl-CoA, isobutyryl- CoA, valeryl-CoA and isovaleryl-CoA.

The enzyme has been described to occur in a number of organisms, in particular in bacteria and in protozoae. In one embodiment the enzyme is from the protozoae Dasytricha ruminantium. In a preferred embodiment the phosphate butyryltransferase is a phosphate butyryltransferase from a bacterium, preferably from a bacterium of the genus Bacillus, Butyrivibrio, Enterococcus or Clostridium, more preferably Enterococcus or Clostridium, and even more preferably from Bacillus subtilis, Bacillus megaterium, Butyrivibrio fibrisolvens, Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium butyricum, Clostridium kluyveri, Clostridium saccharoacetobutylicum, Clostridium sprorogenes or Enterococcus faecalis. Most preferably, the enzyme is from Clostridium acetobutylicum, in particular the enzyme encoded by the ptb gene (Uniprot Accession number F0K6W0; Wiesenborn et al. (Appl. Environ. Microbiol. 55 (1989), 317-322)), from Enterococcus faecalis (Uniprot Accession number K4YRE8; Ward et al. (J. Bacteriol. 181 (1999), 5433-5442)) or from Bacillus subtilis, in particular from strain 168 (Uniprot Accession Number P54530).

In one preferred embodiment, the conversion of an acyl phosphate into a corresponding acyl-CoA is achieved by making use of a phosphate butyryltransferase from Clostridium acetobutylicum, preferably from Clostridium acetobutylicum strain ATCC 824. The amino acid sequence of said protein is shown in SEQ ID NO: 12. It is, of course, not only possible to use an enzyme exactly showing the amino acid of SEQ ID NO: 12. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 12. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91%, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO: 12 and the enzyme has the enzymatic activity of converting an acyl phosphate into a corresponding acyl-CoA. As regards the determination of the sequence identity, the same applies as has been set forth above.

In another preferred embodiment, the conversion of a acyl phosphate into a corresponding acyl-CoA is achieved by making use of a phosphate butyryltransferase from Bacillus subtilis, in particular from strain 168 (Uniprot Accession Number P54530). The amino acid sequence of said protein is shown in SEQ ID NO: 15.

It is, of course, not only possible to use an enzyme exactly showing the amino acid of SEQ ID NO: 15. It is also possible to use an enzyme which comprises a sequence which is at least 60% identical to the amino acid sequence shown in SEQ ID NO: 15. Preferably, the sequence identity is at least 70%, more preferably at least 80%, 85% or 90%, even more preferably 91%, 92%, 93,%, 94%, 95%, 96%, 97%, 98% and particularly preferred at least 99% to SEQ ID NO: 15 and the enzyme has the enzymatic activity of converting an acyl phosphate into a corresponding acyl-CoA. As regards the determination of the sequence identity, the same applies as has been set forth above.

As described above, in a preferred embodiment, the 2-hydroxyaldehyde which is converted in a method according to the present invention is 2-hydroxypropanal and it is converted into propionyl phosphate. In a preferred embodiment the propionyl phosphate is further converted into the corresponding acyl-CoA, i.e. propionyl-CoA, as described herein above. The corresponding reaction may, e.g., occur according to one of the following reaction scheme:

propionyl phosphate propionyl-CoA

The conversion of propionyl phosphate into propionyl-CoA in accordance with this scheme is preferably achieved by making use of a phosphate butyryltransferase, more preferably a phosphate butyryltransferase from Clostridium acetobutylicum, Bacillus subtilis or Enterococcus faecalis, even more preferably the corresponding enzymes as described above.

Moreover, as described above, in a preferred embodiment, the 2-hydroxyaldehyde which is converted in a method according to the present invention is 2,3- dihydroxypropanal and it is converted into 3-hydroxypropionyl phosphate. In a preferred embodiment the 3-hydroxypropionyl phosphate is further converted into the corresponding acyl-CoA, i.e. 3-hydroxypropionyl-CoA, as described herein above. The corresponding reaction may, e.g., occur according to one of the following reaction scheme:

3-hydroxypropionyl phosphate 3-hydroxypropionyl-CoA

The conversion of 3-hydroxypropionyl phosphate into 3-hydroxypropionyl-CoA in accordance with this scheme is preferably achieved by making use of a phosphate butyryltransferase, more preferably a phosphate butyryltransferase from Bacillus subtilis or Enterococcus faecalis, even more preferably the corresponding enzymes as described above.

The method according to the present invention may be carried out in vitro or in vivo. An in vitro reaction is understood to be a reaction in which no cells are employed, i.e. an acellular reaction. Thus, in vitro preferably means in a cell-free system. The term "in vitro" in one embodiment means in the presence of isolated enzymes (or enzyme systems optionally comprising possibly required cofactors). In one embodiment, the enzymes employed in the method are used in purified form.

For carrying out the method in vitro the substrates for the reaction and the enzymes are incubated under conditions (buffer, temperature, co-substrates, co-factors etc.) allowing the enzymes to be active and the enzymatic conversion to occur. The reaction is allowed to proceed for a time sufficient to produce the respective product. The production of the respective products can be measured by methods known in the art, such as liquid chromatography (HPLC) possibly linked to mass spectrometry detection.

The enzymes may be in any suitable form allowing the enzymatic reaction to take place. They may be purified or partially purified or in the form of crude cellular extracts or partially purified extracts. It is also possible that the enzymes are immobilized on a suitable carrier.

The Examples illustrate in vitro reactions according to the invention using phosphoketolases from different origins.

In another embodiment the method according to the invention is carried out in culture, in the presence of an organism, preferably a microorganism, producing at least a phosphoketolase or a sulfoacetaldehyde acetyltransf erase and optionally enzymes which are necessary for providing the 2-hydroxyaldehyde or for further converting the produced acyl phosphate into other compounds, such as a carboxylic acid or the acyl-CoA, as described herein above. A method which employs a microorganism for carrying out a method according to the invention is referred to as an "in vivo" method. The 2-hydroxyaldehyde may either be provided externally or may be produced by the employed microorganism expressing the phosphoketolase or the sulfoacetaldehyde acetyltransferase itself. Such a microorganism expresses at least one enzyme necessary for the enzymatic production of the 2-hydroxyaldehyde. It is also possible to co-culture a microorganism which is capable of producing a 2- hydroxyaldehyde and a microorganism which expresses a phosphoketolase and/ or a sulfoacetaldehyde acetyltransferase so as to convert the 2-hydroxyaldehyde produced by the first microorganism.

Thus, in such embodiments of the invention, a microorganism that produces at least a phosphoketolase or a sulfoacetaldehyde acetyltransferase as described above is used. It is possible to use a microorganism which naturally produces the phosphoketolase or the sulfoacetaldehyde acetyltransferase or a microorganism which had been genetically modified so that it expresses (or overexpresses) a phosphoketolase and/or the sulfoacetaldehyde acetyltransferase. Thus, the microorganism can be a microorganism which naturally expresses a phosphoketolase and/ or a sulfoacetaldehyde acetyltransferase, i.e. which naturally has in its genome a nucleotide sequence encoding a phosphoketolase or a sulfoacetaldehyde acetyltransferase and which expresses it/them. The expression may occur constitutively or in an induced or regulated manner. Microorganisms that inherently, i.e. naturally, have phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity are known in the art and any of them can be used in the context of the present invention. In another embodiment the microorganism can be a microorganism which has been genetically modified by the introduction of a nucleic acid molecule containing a nucleotide sequence encoding a phosphoketolase or a sulfoacetaldehyde acetyltransferase. The nucleic acid molecule can be stably integrated into the genome of the microorganism or may be present in an extrachromosomal manner, e.g. on a plasmid.

Such a genetically modified microorganism can, e.g., be a microorganism that does not naturally have phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity and has been genetically modified to express a phosphoketolase or a sulfoacetaldehyde acetyltransferase or a microorganism which naturally has phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity and which has been genetically modified, e.g. by transformation with a nucleic acid, e.g. a vector, encoding a phosphoketolase or a sulfoacetaldehyde acetyltransferase in order to increase the phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity in said microorganism and/or by insertion of a promoter in front of the endogenous nucleotide sequence encoding the enzyme in order to increase the respective activity in said microorganism.

However, the invention preferably excludes naturally occurring microorganisms as found in nature expressing an enzyme as described above at levels as they exist in nature. Instead, the microorganism of the present invention and employed in a method of the present invention is preferably a non-naturally occurring microorganism, whether it has been genetically modified to express (including overexpression) an exogenous enzyme of the invention not normally existing in its genome or whether it has been engineered to overexpress an exogenous enzyme. Thus, the enzymes and (micro)organisms employed in connection with the present invention are preferably non-naturally occurring enzymes or (microorganisms), i.e. they are enzymes or (micro)organisms which differ significantly from naturally occurring enzymes or microorganism and which do not occur in nature. As regards the enzymes, they are preferably variants of naturally occurring enzymes which do not as such occur in nature. Such variants include, for example, mutants, in particular prepared by molecular biological methods, which show improved properties, such as a higher enzyme activity, higher substrate specificity, higher temperature resistance and the like. As regards the (micro)organisms, they are preferably genetically modified organisms as described herein above which differ from naturally occurring organisms due to a genetic modification. Genetically modified organisms are organisms which do not naturally occur, i.e., which cannot be found in nature, and which differ substantially from naturally occurring organisms due to the introduction of a foreign nucleic acid molecule.

By overexpressing an exogenous or endogenous enzyme as described herein above, the concentration of the enzyme is substantially higher than what is found in nature, which can then unexpectedly force the reaction of the present invention which uses a non-natural for the respective enzyme. Preferably, the concentration of the overexpressed enzyme is at least 5%, 10%, 20%, 30% or 40% of the total host cell protein.

A "non-natural" substrate is understood to be a molecule that is not acted upon by the respective enzyme in nature, even though it may actually coexist in the microorganism along with the endogenous enzyme. This "non-natural" substrate is not converted by the microorganism in nature as other substrates are preferred (e.g. the "natural substrate"). Thus, the present invention contemplates utilizing a non- natural substrate with the enzymes described above in an environment not found in nature.

Thus, it is also possible in the context of the present invention that the microorganism is a microorganism which naturally does not have phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity but which is genetically modified so as to comprise a nucleotide sequence allowing the expression of a phosphoketolase or a sulfoacetaldehyde acetyltransferase. Similarly, the microorganism may also be a microorganism which naturally has phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity but which is genetically modified so as to enhance the phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity, e.g. by the introduction of an exogenous nucleotide sequence encoding a phosphoketolase or a sulfoacetaldehyde acetyltransferase or by the introduction of a promoter for the endogenous gene encoding the enzyme to increase endogenous production to overexpressed (non-natural) levels.

If a microorganism is used which naturally expresses a phosphoketolase or a sulfoacetaldehyde acetyltransferase, it is possible to modify such a microorganism so that the respective activity is overexpressed in the mircroorganism. This can, e.g., be achieved by effecting mutations in the promoter region of the corresponding gene or introduction of a high expressing promoter so as to lead to a promoter which ensures a higher expression of the gene. Alternatively, it is also possible to mutate the gene as such so as to lead to an enzyme showing a higher activity. By using microorganisms which express a phosphoketolase or a sulfoacetaldehyde acetyltransferase, it is possible to carry out the method according to the invention directly in the culture medium, without the need to separate or purify the enzymes.

In one embodiment the organism employed in the method according to the invention is a microorganism which has been genetically modified to contain a foreign nucleic acid molecule encoding a phosphoketolase or a sulfoacetaldehyde acetyltransferase. The term "foreign" or "exogenous" in this context means that the nucleic acid molecule does not naturally occur in said microorganism. This means that it does not occur in the same structure or at the same location in the microorganism. In one preferred embodiment, the foreign nucleic acid molecule is a recombinant molecule comprising a promoter and a coding sequence encoding the respective enzyme in which the promoter driving expression of the coding sequence is heterologous with respect to the coding sequence. "Heterologous" in this context means that the promoter is not the promoter naturally driving the expression of said coding sequence but is a promoter naturally driving expression of a different coding sequence, i.e., it is derived from another gene, or is a synthetic promoter or a chimeric promoter. Preferably, the promoter is a promoter heterologous to the microorganism, i.e. a promoter which does naturally not occur in the respective microorganism. Even more preferably, the promoter is an inducible promoter. Promoters for driving expression in different types of organisms, in particular in microorganisms, are well known to the person skilled in the art.

In a further embodiment the nucleic acid molecule is foreign to the microorganism in that the encoded enzyme is not endogenous to the microorganism, i.e. is naturally not expressed by the microorganism when it is not genetically modified. In other words, the encoded enzyme is heterologous with respect to the microorganism. The foreign nucleic acid molecule may be present in the microorganism in extrachromosomal form, e.g. as a plasmid, or stably integrated in the chromosome. A stable integration is preferred. Thus, the genetic modification can consist, e.g. in integrating the corresponding gene(s) encoding the enzyme(s) into the chromosome, or in expressing the enzyme(s) from a plasmid containing a promoter upstream of the enzyme-coding sequence, the promoter and coding sequence preferably originating from different organisms, or any other method known to one of skill in the art.

The term "microorganism" in the context of the present invention refers to bacteria, as well as to fungi, such as yeasts, and also to algae and archaea. In one preferred embodiment, the microorganism is a bacterium. In principle any bacterium can be used. Preferred bacteria to be employed in the process according to the invention are bacteria of the genus Bacillus, Clostridium, Corynebacterium, Pseudomonas, Zymomonas or Escherichia. In a particularly preferred embodiment the bacterium belongs to the genus Escherichia and even more preferred to the species Escherichia coli. In another preferred embodiment the bacterium belongs to the species Pseudomonas putida or to the species Zymomonas mobilis or to the species Corynebacterium glutamicum or to the species Bacillus subtilis.

It is also possible to employ an extremophilic bacterium such as Thermus thermophilus, or anaerobic bacteria from the family Clostridiae.

In another preferred embodiment the microorganism is a fungus, more preferably a fungus of the genus Saccharomyces, Schizosaccharomyces, Aspergillus, Trichoderma, Kluyveromyces or Pichia and even more preferably of the species Saccharomyces cerevisiae, Schizosaccharomyces pombe, Aspergillus niger, Trichoderma reesei, Kluyveromyces marxianus, Kluyveromyces lactis, Pichia pastoris, Pichia torula or Pichia utilis.

In another embodiment, the method according to the invention makes use of a photosynthetic microorganism expressing at least a phosphoketolase and/or a sulfoacetaldehyde acetyltransferase. Preferably, the microorganism is a photosynthetic bacterium, or a microalgae. In a further embodiment the microorganism is an algae, more preferably an algae belonging to the diatomeae. It is also conceivable to use in the method according to the invention a combination of microorganisms wherein different microorganisms express different enzymes as described above.

In a particularly preferred embodiment the method according to the invention makes use of a microorganism which is capable of producing a 2-hydroxyaldehyde as defined above. Such a microorganism may be either able to produce such a 2- hydroxyaldehyde naturally or due to a genetic modification which allows the microorganism to convert a metabolite or externally provided substrate into such a 2- hydroxyaldehyde. Some organisms have been described to be able to produce a 2- hydroxyaldehyde. For example, some archae bacteria, like Methanocaldococcus jannaschii, have been described to produce 2-hydroxypropanal (lactaldehyde; see Grochowski et al, J. Bacteriol. 188 (2006), 2836-2844; White, RH, Biochemistry 47, (2008), 5037-5046). Moreover, lactaldehyde is known to be a metabolic intermediate in the 1 ,2-propandiol pathway and is produced, e.g, in the L-fucose and R-rhamnose metabolism of E. coli (see, e.g, Boronat et Aguilar, J. Bacteriol. 147 (1981 ), 181-185; Bennet and San, Appl. Microbiol. Biotechnol. 55 (2001 ), 1-9). The genetic modification of microorganisms to express an enzyme of interest will also be further described in detail below.

The phosphoketolase and/ or sulfoacetaldehyde acetyltransferase used in the method according to the invention can be a naturally occurring phosphoketolase or sulfoacetaldehyde acetyltransferase or it can be a phosphoketolase/sulfoacetaldehyde acetyltransferase which is derived from a naturally occurring phosphoketolase/sulfoacetaldehyde acetyltransferase, e.g. by the introduction of mutations or other alterations which, e.g., alter or improve the enzymatic activity, the stability, etc.

The term "phosphoketolase" or "a protein/enzyme having the activity of a phosphoketolase" in the context of the present application also covers enzymes which are derived from a phosphoketolase, which are capable of producing an acyl phosphate from a 2-hydroxyaldehyde as defined above, but which only have a low affinity to their natural substrate or do no longer accept their natural substrate. Such a modification of the phosphoketolase as regards the preferred substrate allows to improve the conversion of a 2-hydroxyaldehyde into an acyl phosphate and to reduce the production of undesired by-products.

The term "sulfoacetaldehyde acetyltransferase" or "a protein/enzyme having the activity of a sulfoacetaldehyde acetyltransferase" in the context of the present application also covers enzymes which are derived from a sulfoacetaldehyde acetyltransferase, which are capable of producing an acyl phosphate from a 2- hydroxyaldehyde as defined above, but which only have a low affinity to their natural substrate or do no longer accept their natural substrate. Such a modification of the sulfoacetaldehyde acetyltransferase as regards the preferred substrate allows to improve the conversion of a 2-hydroxyaldehyde into an acyl phosphate and to reduce the production of undesired by-products.

Methods for modifying and/or improving the desired enzymatic activities of proteins are well-known to the person skilled in the art and include, e.g., random mutagenesis or site-directed mutagenesis and subsequent selection of enzymes having the desired properties or approaches of the so-called "directed evolution".

For example, for genetic modification in prokaryotic cells, a nucleic acid molecule encoding phosphoketolase or a sulfoacetaldehyde acetyltransferase can be introduced into plasmids which permit mutagenesis or sequence modification by recombination of DNA sequences. Standard methods (see Sambrook and Russell (2001 ), Molecular Cloning: A Laboratory Manual, CSH Press, Cold Spring Harbor, NY, USA) allow base exchanges to be performed or natural or synthetic sequences to be added. DNA fragments can be ligated by using adapters and linkers complementary to the fragments. Moreover, engineering measures which provide suitable restriction sites or remove surplus DNA or restriction sites can be used. In those cases, in which insertions, deletions or substitutions are possible, in vitro mutagenesis, "primer repair", restriction or ligation can be used. In general, a sequence analysis, restriction analysis and other methods of biochemistry and molecular biology are carried out as analysis methods. The resulting phosphoketolase/sulfoacetaldehyde acetyltransferase variants are then tested for the desired activity, e.g., enzymatic activity, with an assay as described above and in particular for their increased enzyme activity.

As described above, the microorganism employed in a method of the invention or contained in the composition of the invention may be a microorganism which has been genetically modified by the introduction of a nucleic acid molecule encoding a phosphoketolase and/ or a sulfoacetaldehyde acetyltransferase. Thus, in a preferred embodiment, the microorganism is a recombinant microorganism which has been genetically modified to have an increased phosphoketolase activity and/or an increased sulfoacetaldehyde acetyltransferase activity. This can be achieved e.g. by transforming the microorganism with a nucleic acid encoding a phosphoketolase and/ or a sulfoacetaldehyde acetyltransferase. A detailed description of genetic modification of microorganisms will be given further below. Preferably, the nucleic acid molecule introduced into the microorganism is a nucleic acid molecule which is heterologous with respect to the microorganism, i.e. it does not naturally occur in said microorganism.

In the context of the present invention, an "increased activity" means that the expression and/or the activity of an enzyme, in particular of the phosphoketolase or the sulfoacetaldehyde acetyltransferase, in the genetically modified microorganism is at least 10%, preferably at least 20%, more preferably at least 30% or 50%, even more preferably at least 70% or 80% and particularly preferred at least 90% or 100% higher than in the corresponding non-modified microorganism. In even more preferred embodiments the increase in expression and/or activity may be at least 150%, at least 200% or at least 500%. In particularly preferred embodiments the expression is at least 10-fold, more preferably at least 100-fold and even more preferred at least 1000-fold higher than in the corresponding non-modified microorganism.

The term "increased" expression/activity also covers the situation in which the corresponding non-modified microorganism does not express a corresponding enzyme, e.g. a phosphoketolase or a sulfoacetaldehyde acetyltransferase, so that the corresponding expression/activity in the non-modified microorganism is zero. Preferably, the concentration of the overexpressed enzyme is at least 5%, 10%, 20%, 30%, or 40% of the total host cell protein.

Methods for measuring the level of expression of a given protein in a cell are well known to the person skilled in the art. In one embodiment, the measurement of the level of expression is done by measuring the amount of the corresponding protein. Corresponding methods are well known to the person skilled in the art and include Western Blot, ELISA etc. In another embodiment the measurement of the level of expression is done by measuring the amount of the corresponding RNA. Corresponding methods are well known to the person skilled in the art and include, e.g., Northern Blot.

Methods for measuring the enzymatic activity of the phosphoketolase or sulfoacetaldehyde acetyltransferase are known in the art and have already been described above.

In the context of the present invention the term "recombinant" means that the microorganism is genetically modified so as to contain a nucleic acid molecule encoding an enzyme as defined above as compared to a wild-type or non-modified microorganism. A nucleic acid molecule encoding an enzyme as defined above can be used alone or as part of a vector.

The nucleic acid molecules can further comprise expression control sequences operably linked to the polynucleotide comprised in the nucleic acid molecule. The term "operatively linked" or "operably linked", as used throughout the present description, refers to a linkage between one or more expression control sequences and the coding region in the polynucleotide to be expressed in such a way that expression is achieved under conditions compatible with the expression control sequence.

Expression comprises transcription of the heterologous DNA sequence, preferably into a translatable mRNA. Regulatory elements ensuring expression in fungi as well as in bacteria, are well known to those skilled in the art. They encompass promoters, enhancers, termination signals, targeting signals and the like. Examples are given further below in connection with explanations concerning vectors.

Promoters for use in connection with the nucleic acid molecule may be homologous or heterologous with regard to its origin and/or with regard to the gene to be expressed. Suitable promoters are for instance promoters which lend themselves to constitutive expression. However, promoters which are only activated at a point in time determined by external influences can also be used. Artificial and/or chemically inducible promoters may be used in this context. The vectors can further comprise expression control sequences operably linked to said polynucleotides contained in the vectors. These expression control sequences may be suited to ensure transcription and synthesis of a translatable RNA in bacteria or fungi.

In addition, it is possible to insert different mutations into the polynucleotides by methods usual in molecular biology (see for instance Sambrook and Russell (2001 ), Molecular Cloning: A Laboratory Manual, CSH Press, Cold Spring Harbor, NY, USA), leading to the synthesis of polypeptides possibly having modified biological properties. The introduction of point mutations is conceivable at positions at which a modification of the amino acid sequence for instance influences the biological activity or the regulation of the polypeptide.

Moreover, mutants possessing a modified substrate or product specificity can be prepared. Preferably, such mutants show an increased activity. Alternatively, mutants can be prepared the catalytic activity of which is abolished without losing substrate binding activity.

Furthermore, the introduction of mutations into the polynucleotides encoding an enzyme as defined above allows the gene expression rate and/or the activity of the enzymes encoded by said polynucleotides to be reduced or increased.

For genetically modifying bacteria or fungi, the polynucleotides encoding an enzyme as defined above or parts of these molecules can be introduced into plasmids which permit mutagenesis or sequence modification by recombination of DNA sequences. Standard methods (see Sambrook and Russell (2001 ), Molecular Cloning: A Laboratory Manual, CSH Press, Cold Spring Harbor, NY, USA) allow base exchanges to be performed or natural or synthetic sequences to be added. DNA fragments can be connected to each other by applying adapters and linkers to the fragments. Moreover, engineering measures which provide suitable restriction sites or remove surplus DNA or restriction sites can be used. In those cases, in which insertions, deletions or substitutions are possible, in vitro mutagenesis, "primer repair", restriction or ligation can be used. In general, a sequence analysis, restriction analysis and other methods of biochemistry and molecular biology are carried out as analysis methods.

Thus, in accordance with the present invention a recombinant microorganism can be produced by genetically modifying fungi or bacteria comprising introducing the above- described polynucleotides, nucleic acid molecules or vectors into a fungus or bacterium.

The polynucleotide encoding the respective enzyme, in particular a phosphoketolase or a sulfoacetaldehyde acetyltransferase, is expressed so as to lead to the production of a polypeptide having any of the activities described above, e.g. phosphoketolase activity or sulfoacetaldehyde acetyltransferase activity. An overview of different expression systems is for instance contained in Methods in Enzymology 153 (1987), 385-516, in Bitter et al. (Methods in Enzymology 153 (1987), 516-544) and in Sawers et al. (Applied Microbiology and Biotechnology 46 (1996), 1-9), Billman-Jacobe (Current Opinion in Biotechnology 7 (1996), 500-4), Hockney (Trends in Biotechnology 12 (1994), 456-463), Griffiths et al., (Methods in Molecular Biology 75 (1997), 427-440). An overview of yeast expression systems is for instance given by Hensing et al. (Antonie van Leuwenhoek 67 (1995), 261-279), Bussineau et al. (Developments in Biological Standardization 83 (1994), 13-19), Gellissen et al. (Antonie van Leuwenhoek 62 (1992), 79-93, Fleer (Current Opinion in Biotechnology 3 (1992), 486-496), Vedvick (Current Opinion in Biotechnology 2 (1991 ), 742-745) and Buckholz (Bio/Technology 9 (1991 ), 1067-1072).

Expression vectors have been widely described in the literature. As a rule, they contain not only a selection marker gene and a replication-origin ensuring replication in the host selected, but also a bacterial or viral promoter, and in most cases a termination signal for transcription. Between the promoter and the termination signal there is in general at least one restriction site or a polylinker which enables the insertion of a coding DNA sequence. The DNA sequence naturally controlling the transcription of the corresponding gene can be used as the promoter sequence, if it is active in the selected host organism. However, this sequence can also be exchanged for other promoter sequences. It is possible to use promoters ensuring constitutive expression of the gene and inducible promoters which permit a deliberate control of the expression of the gene. Bacterial and viral promoter sequences possessing these properties are described in detail in the literature. Regulatory sequences for the expression in microorganisms (for instance E. coli, S. cerevisiae) are sufficiently described in the literature. Promoters permitting a particularly high expression of a downstream sequence are for instance the T7 promoter (Studier et al., Methods in Enzymology 185 (1990), 60-89), lacUV5, trp, trp-lacUV5 (DeBoer et al., in Rodriguez and Chamberlin (Eds), Promoters, Structure and Function; Praeger, New York, (1982), 462-481 ; DeBoer et al., Proc. Natl. Acad. Sci. USA (1983), 21-25), Ip1 , rac (Boros et al., Gene 42 (1986), 97-100). Inducible promoters are preferably used for the synthesis of polypeptides. These promoters often lead to higher polypeptide yields than do constitutive promoters. In order to obtain an optimum amount of polypeptide, a two-stage process is often used. First, the host cells are cultured under optimum conditions up to a relatively high cell density. In the second step, transcription is induced depending on the type of promoter used. In this regard, a tac promoter is particularly suitable which can be induced by lactose or IPTG (=isopropyl^-D-thiogalactopyranoside) (deBoer et al., Proc. Natl. Acad. Sci. USA 80 (1983), 21-25). Termination signals for transcription are also described in the literature.

The transformation of the host cell with a polynucleotide or vector as described above can be carried out by standard methods, as for instance described in Sambrook and Russell (2001 ), Molecular Cloning: A Laboratory Manual, CSH Press, Cold Spring Harbor, NY, USA; Methods in Yeast Genetics, A Laboratory Course Manual, Cold Spring Harbor Laboratory Press, 1990. The host cell is cultured in nutrient media meeting the requirements of the particular host cell used, in particular in respect of the pH value, temperature, salt concentration, aeration, antibiotics, vitamins, trace elements etc.

When the method according to the invention is carried out in vivo by using an organism/microorganism providing the respective enzyme activities, the organism, preferably microorganism, is cultivated under suitable culture conditions allowing the occurrence of the enzymatic reaction. The specific culture conditions depend on the specific organism/microorganism employed but are well known to the person skilled in the art. The culture conditions are generally chosen in such a manner that they allow the expression of the genes encoding the enzymes for the respective reactions. Various methods are known to the person skilled in the art in order to improve and fine-tune the expression of certain genes at certain stages of the culture such as induction of gene expression by chemical inducers or by a temperature shift.

In another embodiment, the method of the invention comprises the step of providing the organism, preferably the microorganism carrying the respective enzyme activity or activities in the form of a (cell) culture, preferably in the form of a liquid cell culture, a subsequent step of cultivating the organism, preferably the microorganism in a fermenter (often also referred to a bioreactor) under suitable conditions allowing the expression of the respective enzyme and further comprising the step of effecting an enzymatic conversion of a method of the invention as described herein above. Suitable fermenter or bioreactor devices and fermentation conditions are known to the person skilled in the art. A bioreactor or a fermenter refers to any manufactured or engineered device or system known in the art that supports a biologically active environment. Thus, a bioreactor or a fermenter may be a vessel in which a chemical reaction like the method of the present invention is carried out which involves an organisms, preferably microorganisms and/or active substances, i.e., the enzyme(s) described above derived from such organisms or organisms harbouring the above described enzyme(s). In a bioreactor or a fermenter, this process can either be aerobic or anaerobic. These bioreactors are commonly cylindrical, and may range in size from litres to cubic metres, and are often made ofstainless steel. In this respect, without being bound by theory, the fermenter or bioreactor may be designed in a way that it is suitable to cultivate the organisms, preferably microorganisms, in, e.g., a batch-culture, feed-batch-culture, perfusion culture or chemostate-culture, all of which are generally known in the art.

The culture medium can be any culture medium suitable for cultivating the respective organism or microorganism.

The present invention also relates to a composition containing

(a) a 2-hydroxyaldehyde and a phosphoketolase; or

(b) a 2-hydroxyaldehyde and a sulfoacetaldehyde acetyltransferase; or

(c) a 2-hydroxyaldehyde and a phosphoketolase and a sulfoacetaldehyde acetyltransferase; or

(d) a 2-hydroxyaldehyde and a microorganism expressing a phosphoketolase; or

(e) a 2-hydroxyaldehyde and a microorganism expressing a sulfoacetaldehyde acetyltransferase; or

(f) a 2-hydroxyaldehyde and a microorganism expressing a phosphoketolase and a sulfoacetaldehyde acetyltransferase, wherein the 2-hydroxyaldehyde responds to the following formula:

2-hydroxyaldehyde wherein R ¹ and R ² are selected independently from H, CH3, CH ₂ OH and C ₂ Hs and wherein if R ¹ is H, R ² cannot be H.

The phosphoketolase/ sulfoacetaldehyde acetyltransferase can be a phosphoketolase/ sulfoacetaldehyde acetyltransferase as defined above in connection with the method according to the invention. The microorganism contained in the composition can be any suitable microorganism which expresses a phosphoketolase and/or a sulfoacetaldehyde acetyltransferase, in particular a microorganism as described herein above in connection with the method according to the invention.

The present invention furthermore relates to the use of a phosphoketolase or of a sulfoacetaldehyde acetyltransferase or of a microorganism expressing a phosphoketolase and/or sulfoacetaldehyde acetyltransferase for the production of an acyl phosphate from a 2-hydroxyaldehyde as defined herein above. As regards the phosphoketolase/ sulfoacetaldehyde acetyltransferase and the microorganism, the same applies as has been set forth above in connection with a method according to the invention.

Figure 1 shows schematically the conversion of a 2-hydroxyaldehyde into the corresponding acyl phosphate.

Figure 2 shows schematically the conversion of acyl phosphate into the corresponding carboxylic acid.

Figure 3 shows schematically the conversion of acyl phosphate into the corresponding acyl-CoA.

Figure 4 shows schematically the conversion of 2-hydroxypropanal into propanoic acid or propionyl-CoA.

Figure 5 shows schematically the conversion of 2,3-dihydroxypropanal into 3- hydroxypropanoic acid or 3-hydroxypropionyl-CoA.

In this specification, a number of documents including patent applications are cited. The disclosure of these documents, while not considered relevant for the patentability of this invention, is herewith incorporated by reference in its entirety. More specifically, all referenced documents are incorporated by reference to the same extent as if each individual document was specifically and individually indicated to be incorporated by reference.

The invention will now be described by reference to the following examples which are merely illustrative and are not to be construed as a limitation of the scope of the present invention. EXAMPLES

Example 1 : Cloning, expression and purification of phosphoketolases

Gene synthesis, cloning and expression of recombinant enzymes

The sequences of phosphoketolases inferred from the genomes of prokaryotic organisms were generated by oligonucleotide concatenation to fit the codon usage of E. coli (genes were commercially synthesized by GeneArt®). A stretch of 6 histidine codons was inserted after the methionine initiation codon to provide an affinity tag for purification. The genes thus synthesized were cloned in a modified pUC18 expression vector (New England Biolabs) containing a modified Multiple Cloning Site (MCS). The genes of interest were cloned at Pad and Notl restriction sites.

Competent MG1655 E. coli cells were transformed with these vectors using standard heat shock procedure. The transformed cells were grown in LB-ampicillin medium for 24h at 30°C, 160 rpm shaking.

The cells were collected by centrifugation at 4°C, 10,000 rpm for 20 min and the pellets were stored at -80°C.

Protein purification and concentration

The pellets from 200 ml of cultured cells were thawed on ice and resuspended in 3 ml of 50 mM Tris-HCI pH 7.5 containing 300 mM NaCI, 5 mM MgCI ₂₎ 1 mM DTT and 10 mM Imidazole. 10 μΙ of lysonase (Merck) was added. Cells were incubated 10 minutes at room temperature and then returned to ice for 20 minutes. Cell lysis was completed by sonication for 2 x 30 seconds. The bacterial extracts were then clarified by centrifugation at 4°C, 10,000 rpm for 20 min. The clarified bacterial lysates were loaded on PROTINO-1000 Ni-TED column (Macherey-Nagel) allowing adsorption of 6-His tagged proteins. Columns were washed and the enzymes of interest were eluted with 4 ml of 50 mM Tris-HCI pH 7.5 containing 300 mM NaCI, 5 mM MgCI ₂ , 1 mM DTT, 250 mM Imidazole. Eluates were then concentrated, desalted on Amicon Ultra-4 10 kDa filter unit (Millipore) and enzymes were resuspended in 50 mM Tris- HCI pH 7.5. The enzyme preparation was complemented with 10% glycerol prior to long-term storage. Protein concentrations were quantified by direct UV 280 nm measurement on the NanoDrop 1000 spectrophotometer (Thermo Scientific). The purity of proteins thus purified varied from 70 % to 90 %. Example 2: Study of the formation of 3-hydroxypropionyl phosphate from 2,3- dihydroxypropanal, catalyzed by phosphoketolase

Enzymatic reactions

The enzymatic reactions were carried out under the following conditions:

50 mM Tris-HCI pH 7.5

25 mM Potassium phosphate pH 7.5

5 mM Thiamine pyrophosphate (TPP)

5 mM MgCI ₂

23 mM Sodium fluoride

8 mM Sodium iodoacetate

1.9 mM L-Cysteine hydrochloride

50 mM 2,3-Dihydroxypropanal (D,L-glyceraldehyde) (Sigma)

The pH was adjusted to 7.5

Each enzymatic reaction was started by adding 3 mg/ml of purified recombinant phosphoketolase (PKT).

Control assays were performed in which either no enzyme was added, or no substrate was added.

Incubations were run overnight with shaking at 37° C. 3-hydroxypropionyl phosphate formation was studied through the detection of iron (III) 3-hydroxypropionyl- hydroxamate using the following procedure (Racker E., Methods Enzymol. 5, 1962, 276-280): 0.1 ml of hydroxylamine hydrochloride (2 M, pH 6.5) was added to 0.1 ml of reaction mixture. After 10 min of incubation at room temperature the samples were acidified with 35 μΙ of 30% trichloroacetic acid. 35 μΙ of 8 M HCI and 35 μΙ of FeCI ₃ reagent (10% FeCI ₃ in 0.1 M HCI) were then added. The samples were further clarified by centrifugation and the absorbance of ferric 3-hydroxypropionyl- hydroxamate complex was measured at 505 nm.

A low signal of absorbance was observed in the control assays in which either no phosphoketolase was added, or no 2,3-dihydrpoxypropanal was added. Absorbance values of the enzymatic samples corrected by subtraction of the control assay without enzyme, are shown in Table 1. Table 1

Example 3: Study of the formation of propionyl phosphate from 2- hydroxypropanal catalyzed by phosphoketolase

The enzymatic assays were carried out according to the protocol described in Example 2. 2-hydroxypropanal (lactaldehyde) was used as substrate instead of 2,3 dihydroxypropanal.

Hydroxamate-based colorimetric assay

Propionyl phosphate formation was studied through the detection of iron (III) propionyi-hydroxamate using the procedure described in Example 2. A low signal of absorbance was observed in the control assays in which either no phosphoketolase was added, or no 2-hydroxypropanal was added. Absorbance values of the enzymatic samples corrected by subtraction of the control assay without enzyme, are shown in Table 2.

Table 2

Thus, different phosphoketolases were shown to catalyze the conversion of a 2- hydroxyaldehyde into the corresponding acyl phosphate.

Example 4: Cloning, expression and purification of sulfoacetaldehyde acetyltransferases

Gene synthesis, cloning and expression of recombinant proteins

The sequences of the studied enzymes inferred from the genomes of prokaryotic organisms were generated by oligonucleotide concatenation to fit the codon usage of E. coli (genes were commercially synthesized by GeneArt®). A stretch of 6 histidine codons was inserted after the methionine initiation codon to provide an affinity tag for purification. The genes thus synthesized were cloned in a pET-25b(+) expression vector (vectors were constructed by GeneArt®).

Competent E. coli BL21 (DE3) cells (Novagen) were transformed with these vectors according to standard heat shock procedure. The transformed cells were grown with shaking (160 rpm) using ZYM-5052 auto-induction medium (Studier FW, Prot. Exp. Pur. 41 , (2005), 207-234) for 7h at 30°C and protein expression was continued at 8°C overnight (approximately 16 h). The cells were collected by centrifugation at 4°C, 10,000 rpm for 20 min and the pellets were stored at -80°C.

Protein purification and concentration

The pellets from 200 ml of culture cells were thawed on ice and resuspended in 5 ml of 50 mM Tris-HCI buffer pH 7.5 containing 300 mM NaCI, 10 mM MgCI ₂ , 10 mM imidazole and 1 mM DTT. Twenty microliters of lysonase (Novagen) were added. Cells were incubated 10 minutes at room temperature and then returned to ice for 20 minutes. Cell lysis was completed by sonication for 2 x 30 seconds. The bacterial extracts were then clarified by centrifugation at 4°C, 4000 rpm for 40 min. The clarified bacterial lysates were loaded onto a PROTINO-2000 Ni-TED column ( acherey-Nagel) allowing adsorption of 6-His tagged proteins. Columns were washed and the enzymes of interest were eluted with 6 ml of 50 mM Tris-HCI buffer pH 7.5 containing 300 mM NaCI, 5 mM MgCI2, 1 mM DTT and 250 mM imidazole. Eluates were then concentrated, desalted on Amicon Ultra-4 10 kDa filter unit (Millipore) and enzymes were resuspended in 50 mM Tris-HCI buffer pH 7.5. The purity of proteins thus purified varied from 70% to 90% as estimated by SDS-PAGE analysis. Protein concentrations were determined by direct UV 280 nm measurement on the NanoDrop 1000 spectrophotometer (Thermo Scientific) or by Bradford assay (BioRad).

Example 5: HPLC-based analysis of the conversion of D, L-lactaldehyde (2- hydroxypropanal) into propionyl phosphate and further into propionic acid

The phosphoketolases were expressed and purified as described in Example 1. The sulfoacetaldehyde acetyltransferases were expressed as described in Example 4.

Enzyme reaction

The enzymatic reactions were carried out under the following conditions:

50 mM Tris-HCI pH 7.5

With or without 25 mM sodium phosphate pH 7.5

0.6 mM thiamine pyrophosphate (TPP)

1 mM MgCI ₂

1.9 mM L-cysteine hydrochloride

50 mM D, L-lactaldehyde (Sigma-Aldrich)

2.8 mg/ ml purified enzyme Total volume 150 μΙ.

A control assay was performed in which no enzyme was added. Enzymatic assays were conducted overnight at 37°C. The formation of propionic acid was studied using HPLC-based analysis.

HPLC-based method

The enzymatic reactions were stopped by a 5-min incubation at 80 °C. Then, 150 μΙ MeCN was added in the medium, and the assay tubes were centrifuged. 100 μΙ of the clarified supernatant was filtered, and transferred into a clean vial.

HPLC analyses were performed using a 260 Infinity LC System (Agilent), equipped with a refractometer detector and a column heating module. 5 μΙ sample was separated on Hi-Plex H column (100 x 7.7 mm, 8 pm particle size, column temp. 65°C) equipped with a PL Hi-Plex H Guard Column (50 x 7.7 mm). The mobile phase consisted of aqueous sulfuric acid (1 mM) and was run with a flow rate of 0.8 ml/min. Retention time of D, L-lactaldehyde and propionic acid under these conditions were 4.94 and 6.62 min, respectively.

Several phosphoketolases or sulfoacetaldehyde acetyltransferases were able to catalyze the conversion of D, L-lactaldehyde into propionic acid (Table 3). The formation of propionic acid was improved in the presence of inorganic phosphate, indicating that the conversion takes place through an acyl-phosphate as intermediate. The acyl phosphate which is rather unstable is converted into propionic acid by way of spontaneous hydrolysis.

Example 6: HPLC-based analysis of the conversion of D, L-glyceraldehyde (2,3- hydroxypropanal) into 3-hydroxypropionyl phosphate and further into 3- hydroxypropionic acid

All the phosphoketolases were expressed and purified as described in Example 1. The sulfoacetaldehyde acetyltransferases were expressed as described in Example 4.

Enzyme reaction

The enzymatic reactions were carried out under the following conditions:

50 mM Tris-HCI pH 7.5

With or without 25 mM sodium phosphate pH 7.5

0.6 mM thiamine pyrophosphate (TPP)

1 mM MgCI ₂

1.9 mM L-cysteine hydrochloride

50 mM D, L-glyceraldehyde (Sigma)

2.8 mg/ ml purified enzyme

Total volume of the reaction was 150 μΙ.

A control assay was performed in which no enzyme was added. Enzymatic assays were conducted overnight at 37°C. The formation of 3-hydroxypropionic acid was studied using HPLC-based analysis.

HPLC-based method

The enzymatic reactions were stopped by a 5-min incubation at 80 °C. Then, 150 μΙ MeCN was added in the medium, and the assay tubes were centrifuged. 100 μΙ of the clarified supernatant was filtered, and transferred into a clean vial.

The amount of 3-hydroxypropionic acid produced was measured using a HPLC- based procedure. HPLC analysis was performed using a 1260 Infinity LC System Agilent, equipped with column heating module, and refractometer. 5 μΐ of samples were separated using 3 columns connected in series as follows:

1. Hi-Plex guard column (50 x 7.7 mm, 8 pm particle size) (Agilent)

2. Hi-Plex column ( 00 x 7.7 mm, 8 pm particle size) (Agilent)

3. Zorbax SB-Aq column (250 x 4.6 mm, 5 pm particle size, column temp. 65 °C) (Agilent).

The mobile phase consisted of aqueous sulfuric acid (1 mM), mobile phase flow rate was 0.5 ml/min. Retention time of D, L-glyceraldehyde and 3-hydroxypropionic acid under these conditions were 12.12 and 14.67 min, respectively. Several phosphoketolases or sulfoacetaldehyde acetyltransferases were able to catalyze the conversion of D, L-glyceraldehyde into 3-hydroxypropionic acid (Table 4). The conversion is considered to take place via the intermediate 3- hydroxypropionyl phosphate which is rather unstable and is spontaneously hydrolyzed to 3-hydroxypropionic acid.

Table 4 uniprot

enzyme organism accession 3-hydroxypropionic number acid mM

Sulfoacetaldehyde Castellaniella

Q84H44 0.2 acetyltransferase defragans

Sulfoacetaldehyde Alcaligenes

Q84H41 0.1 acetyltransferase xyloxydans

Sulfoacetaldehyde Roseovarius

A3SR25 0.3 acetyltransferase nubinhibens

Sulfoacetaldehyde Desulfonispora

Q93PS3 0.1 with 50 mM acetyltransferase thiosulfatigenes

phopshate Streptococcus

Phosphoketolase A8AV21 2.1

gordonii

Lactococcus

Phosphoketolase A9QST6 0.8

lactis

Lactococcus

Phosphoketolase D5H215 0.3

crispatus

control without enzyme 0.2

Sulfoacetaldehyde Castellaniella

Q84H44 0.1 acetyltransferase defragans

Sulfoacetaldehyde Alcaligenes

Q84H41 0.1 acetyltransferase xyloxydans

Sulfoacetaldehyde Roseovarius

A3SR25 0.4 acetyltransferase nubinhibens

Sulfoacetaldehyde Desulfonispora

without 50 Q93PS3 0.2

acetyltransferase thiosulfatigenes

mM

phosphate Streptococcus

Phosphoketolase A8AV21 1.1

gordonii

Lactococcus

Phosphoketolase A9QST6 1.3

lactis

Lactococcus

Phosphoketolase D5H215 1.2

crispatus

control without enzyme 0.1