BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention is related to a novel xylanase composition and a method for its production Specifically, the invention is related to a purified xylanase composition derived from Acidothermus sp , and particularly Acidothermus cellulolyticus, and the use of that enzyme in bleaching pulp and paper and treating feed compositions

2. State of the Art

Xylanases are known to be produced by a number of different microorganisms Several different xylanolytic enzymes are generally produced by a microorganism each of the xylanases acting to attack different bonds in the wood complex Attempts to use enzymes derived from both fungal and bacterial sources in industπal processes, e g , for enhancing dehgnification and bπghtenmg while loweπng or eliminating the use of chlonne in the bleaching of lignocellulosic pulp in the paper industry or for improving the value of animal feed have been descπbed in the literature

Xylanases, e g , endo-β-xylanases (EC 32 1 8), which hydrolyze the xylan backbone chain, have been studied for their use in bleaching lignocellulosic matenal For example in U S Patent No 5,179,021 , the combination of xylanase and oxygen treatment in the bleaching of pulp is disclosed as being particularly useful In PCT Application Publication No WO 92/03541 , a method of dissolving hemicellulose with hemicellulases derived from the fungus Trichoderma reesei is disclosed The search for xylanases, however has focused on thermophilic and alkalophilic xylanases which are useful under pulp bleaching conditions utilizing high temperatures and alkali However, the use of oxygen or ozone bleaching generally occurs at a lower pH Accordingly, it would be advantageous to discover a low pH xylanase which has significant activity at high temperatures

Recently, several thermophi c xylanases from fungal and bacteπal microorganisms have been identified For example, a thermophilic xylanase has been isolated from Actinomadura reciassified as Microtetraspora having an optimal pH of 6 0-7 0 and temperature range of 70- 80°C (Holtz, C et al Antonie van Leewenhoek 59 1-7, 1991) EP 473 545 discloses that the bacteπal strain Thermomonospora fusca produces thermostable xylanases active at temperatures 10-90°C, preferably, 50-80°C over a wide pH range, i e , from about 5-10, with the more preferred range between 6 6-9 5 In addition W092/18612 discloses a xylanase enzyme deπved from the genus, Dictyoglomus, having activity over a broad pH range (5 0-9 0) and thermostability at

temperatures ranging from 60-90°C The thermophilic cellulolytic bacteria Acidothermus cellulotyticus is descnbed in Mohagheghi et al , Int J Systematic Bact vol 36, no 3, pp 435-443 (1986), and the production of cellulase is descπbed in Shiang et al , Appl Microb Biotech , vol 34, pp 591-597 (1991) However, neither reference descπbes a puπfied xylanase which may be useful at low pH and high temperature

Xylanases have also been useful in animal feeds to enable animals to digest the feeds more efficiently One result of adding xylanase to feed is an improvement in the Feed Conversion Ratio (FCR) of a feed without increasing its cost per unit weight The FCR of a feed is the ratio of the amount of feed consumed relative to the weight gain of the animal A low FCR indicates that a given amount of feed results in a growing animal gaining proportionately more weight This means that the animal is able to utilise the feed more efficiently One way in which the FCR can be reduced is to improve its digestibility by an animal thereby increasing the nutπtional benefit which the animal can deπve from it

However, there are vaπous constraints on the digestibility of the nutritional components of a feed such as its starch, fat, protein and ammo acid content These constraints include

(i) the viscosity of mateπals present in the animal's gut Such viscosity is due, at least in part, to soluble non-starch polysacchaπdes such as mixed-linked β-glucans and arabinoxylans, (ii) entrapment of nutnents within the cell walls of the feed, particularly those of the aleurone layer in cereals Such entrapment is caused by the high levels of non-starch polysaccharides in the cell walls of cereals which are relatively resistant to break-down by the animal's digestive system This prevents the nutrients entrapped within the cells from being nutπtionally available to the animal and (in) a deficiency in endogenous enzyme activity, both of the animal and of the gut microbial population particularly in a young animal

The above problems which interfere with digestibility are particularly noticeable in the case of cereal-based diets, such as those having a high wheat content

Due to the problem of poor digestibility of nutnents from the feed, it is normally necessary to formulate feeds to contain higher levels of energy and protein providing mateπals in order to meet the nutπtional demands of animals

There is now a substantial body of evidence showing that incoφorating certain (supplementary) enzymes in cereal-based animal feeds can be advantageous in reducing the viscosity of mateπal present in the animal's gut This reduction can be achieved by enzymes such as xylanases which hydrolyse soluble xylans thereby reducing digesta viscosity which is an important constraint on the process of digestion

The xylanases which are added as supplements must be stable and active at the pH and temperature conditions found within the gastrointestinal (Gl) tract of the target animal If they are not stable and active when exposed to such in vivo conditions, then they will not be able to reduce digesta viscosity to any significant extent It is presently known to include xylanases as a supplement in an animal feed deπved from fungi such as Trichoderma longibrachiatum,

Aspergillus niger and Humicola msolens Bedford and Classen (The Journal of Nutπtion, vol 122, pp 560-569) disclose that there is a significant correlation between digesta viscosity measured in vivo in the case of broiler chickens and bodyweight gam and FCR values In the case of wheat and rye-based diets fed to poultry, it was shown that as much as 70-80% of the vaπations in the weight gam and FCR are based upon differences in intestinal viscosity alone This highlights the importance of digesta viscosity in cereal-based feeds containing high levels of soluble arabinoxylans As digesta viscosity increases, it reduces the digestibility of all nutnents by mterfeπng with the diffusion of pancreatic enzymes substrates and the end products of the digestion process However, the use of enzyme supplements, such as xylanase, in animal feed is complicated by the processing requirements for grain supplements Often, such enzyme supplements are obtained by impregnating the enzyme onto a physiologically acceptable earner, such as a cereal The impregnated earner is mixed with the other components of the feed and then pressed into cubes or pellets for feeding directly to animals The processes which have been developed make use of relatively high temperatures This is firstly to improve the efficiency of the manufactuπng process and secondly to produce feeds which are free from harmful bactena, particularly Salmonella In addition, the use of high temperatures improves the quality and durability of the resulting cubes and pellets, increases the range of ingredients which can be efficiently handled and also increases the level of liquid ingredients, such as fat and molasses which can be incoφorated into the feed

Processing techniques for feed components currently employ relatively high temperatures for a relatively long peπod Further, the mixture is subjected to relatively high pressures duπng pelleting to increase the durability of the cubes or pellets formed One of the processing methods which has been developed to improve the nutπtional properties of the feed is steam pelleting This method includes the step of treating the compounded feed with steam to increase its temperature and moisture content This step is termed conditioning Conditioning lasts from a few seconds up to several minutes depending on the type and formulation of the feed The temperature in the conditioner may πse to 100°C Afterwards, the feed is passed through a pelleting die which causes a rapid increase in its temperature due to fπction Recently, a new device for pre-treatment or conditioning of feeds has been introduced called an expander This device allows sustained conditioning under pressure followed by

pelleting According to this technique, vanous feed components which have previously been subjected to steam-conditioning are fed into a compression screw into which more steam is injected, and the mass is then subjected to increasing pressure and shear action and then forced through a vanable exit gap The compressed product, after reduction in particle size, is fed into a standard pelleting press The dwell time of the feed components in the expander is about 5-20 seconds, and the temperature reached may be as high as 145°C A compression pressure of about 3.5 MPa is reached, but the build-up of both temperature and pressure is very quick and both fall rapidly as the product is expelled through the exit gap The use of expanders is advantageous because they effectively eliminate harmful bacteπa, particularly Salmonella Furthermore, it is possible to include relatively high levels of fat and other liquid ingredients in the mixture pπor to pelleting In addition, the cooking and pressure/shear action results in greater starch gelatinisation

Unfortunately, the high temperature and high pressure processing conditions characteπstic of the expander and pelleting technology, particularly when applied in the moist conditions normally encountered dunng pelleting, are potentially destructive to certain feed components This is particularly true of any enzymes, including xylanases, which are present Thus, the pnor art enzymes have generally had the problem that they are not sufficiently stable under the processing conditions of commercial pelleting operations to allow economical use of such pelleting techniques Accordingly, even though partial solutions to the problem of enzyme stability dunng feed processing are available, none of them solves the problem in a totally effective manner

SUMMARY OF THE INVENTION

It is an object of the invention to provide for a novel xylanase having significant activity at low pH and high temperature

It is a further object of the invention to provide a novel method for bleaching lignocellulosic pulp.

It is a further object of the invention to provide improved means of treating feed grains to improve their digestibility According to the present invention, a purified xylanase is provided which is characterized by the following physical properties a pH optimum of about 3 6 to 4 2 and a molecular weight of about 50-55 kD as determined by gel filtration Preferably the xylanase is derived from Acidothermus sp , more preferably from Acidothermus cellulolyticus and most preferably from Acidothermus cellulolyticus ATCC 43068

In a composition embodiment of the invention, a purified xylanase composition is provided, which xylanase is derived from Acidothermus sp and has a pH optimum of about 3.6 to 4.2 and a molecular weight of about 50-55 kD, as determined by gel filtration

In another composition embodiment of the invention, a feed additive is provided wherein said feed additive comprises a xylanase derived from Acidothermus sp. and has a pH optimum of about 3.6 to 4.2 and a molecular weight of about 50-55 kD, as determined by gel filtration.

In a method embodiment of the present invention, xylanase isolated from a fermentation culture of Acidothermus sp. is used in the bleaching of a lignocellulosic pulp In another method embodiment of the present invention, a feed additive comprising a xylanase derived from Acidothermus sp having a pH optimum of about 3 6 to 4 2 and a molecular weight of about 50-55 kD, as determined by gel filtration is used to improve the quality of a grain based animal feed

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates the temperature dependency of activity of xylanase according to the invention on RBB-xylan at a pH of 4.5 for 10 minutes

Fig. 2 illustrates the half-life of xylanase treated at a range of temperature Fig 3 illustrates the relative activity of xylanase of the invention at a range of pH and depicting the pH optimum

Fig. 4 illustrates the stability of xylanase of the invention over time after treatment at a pH of 3.3.

DETAILED DESCRIPTION OF THE INVENTION According to the present invention, a purified xylanase is provided which is characterized by the following physical properties a pH optimum of about 3 6 to 4 2, a molecular weight of about 50-55 kD as determined by gel filtration, a pl of about 6 0-6 5, and a temperature optimum of about 70-80 ^' C. Preferably, the xylanase is derived from Acidothermus sp., more preferably from Acidothermus cellulolyticus and most preferably from Acidothermus cellulolyticus ATCC 43068 (deposited with the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Maryland, USA 20852 ) Acidothermus cellulolyticus is taxonomically described in Int J Systematic Bact , vol 36, pp 435-443 (1986) and in U.S Patent No. 5,366,884, which are herein incorporated by reference In another aspect of the invention, the xylanase derived from Acidothermus sp , and preferably from Acidothermus cellulolyticus, is used in the preparation of a cereal based animal

feed In such a cereal-based feed, the cereal is preferably at least one of wheat barley maize sorghum, rye, oats, tπticale and rice It is particularly preferred that the cereal should be wheat

The cereal-based feed according to the present invention may be provided to animals such as turkeys, geese, ducks, sheep and cows It is however particularly preferred that the feed is provided to pigs or to poultry, and in particular broiler chickens The cereal-based feed preferably includes 0 00001-10 g of xylanase protein per kilo of the feed, more preferably includes about 0001-1 g of xylanase protein per kilo of the feed, and most preferably 0 001-0 1 g of xylanase protein per kilo of the feed The cereal-based feed compnses at least 20% by weight of cereal More preferably, it should include at least 30% by weight of the cereal and most preferably at least 50% by weight of the cereal The cereal can be any of those previously mentioned, with wheat being particularly preferred

Although the cereal component of a cereal-based feed constitutes a source of protein it is usually necessary to include sources of supplementary protein in the feed such as those deπved from fish-meal, meat-meal or vegetables Sources of vegetable proteins include at least one of full fat soybeans, rapeseeds, canola, soybean-meal rapeseed-meal and canola-meal As compared to conventional feeds, the relative amount of the additional protein sources such as fish-meal meat-meal or vegetable protein can be reduced by adopting the teaching of the present invention resulting in significant cost savings This is because the relative cost of cereals is significantly less than that of conventional protein supplements In view of this, a feed can be prepared according to the teaching of the present invention having the same nutritional value in terms of available energy, am o acids and protein as a conventional feed but which includes a higher relative proportion of cereal and a lower relative proportion of protein supplements It is also found that the inclusion of a thermostable xylanase in an animal feed has the effect that reduced levels of energy supplements such as fats and oils need to be included in order to achieve a feed having a certain level of performance

The inclusion of a thermostable xylanase in an animal feed in accordance with the present invention enables the crude protein value and/or digestibility and/or ammo acid content and/or digestibility coefficients of the feed to be increased which permits a reduction in the amounts of alternative protein sources and/or am o acids supplements which had previously been necessary ingredients of animal feeds When the protein digestibility coefficient and/or the content of available crude protein of wheat is increased by the addition of the thermostable xylanase, major savings can be found in the reduced levels of protein and/or energy supplements which have conventionally needed to be added Alternatively when only the ammo acid content or digestibility coefficient values are increased by the addition of the thermostable xylanase the major savings are to be found in the reduced levels of am o acid supplements which have conventionally needed to be added to the feeds

The feed provided by the present invention may also include other enzyme supplements such as one or more of β-glucanase, glucoamylase, mannanase, α-galactosidase, phytase, lipase, α-arabmofuranosidase, protease, α-amylase esterase, oxidase, oxido-reductase and pectinase It is particularly preferred to include a protease as a further enzyme supplement such as a subtilism deπved from the genus Bacillus Such subtilisms are for example descπbed in detail in U S Patent No 4,760,025

A suitable feed in accordance with the present invention can be obtained by prepaπng a feed additive compnsing a physiologically acceptable earner and the thermo-stable xyianase, and then mixing this additive in amounts of 0 01-50 g per kilo with the other components constituting the animal feed (including the cereal and other sources of protein supplement), more preferably 0 1-10 g/kg and most preferably about 1 g/kg

The physiologically acceptable earner in this aspect of the present invention is preferably a cereal or deπved from a cereal Such cereals include milled wheat maize soya sugars starches or a by-product of any of these Such earners are conventional in this technical art, and so are not descπbed in any further detail

The feed additive according to this aspect of the present invention is combined with other feed components to produce a cereal-based feed Such other feed components include one or more other (preferably thermostable) enzyme supplements, vitamin feed additives mineral feed additives and ammo acid feed additives The resulting (combined) feed additive including possibly several different types of compounds can then be mixed in an appropnate amount with the other feed components such as cereal and protein supplements to form an animal feed Processing of these components into an animal feed can be performed using any of the currently used processing apparatuses such as a double-pelleting machine, a steam pelleter, an expander or an extruder The presence of the thermostable xylanase in the resulting cereal-based feed has the effect of reducing its FCR The xylanase may alternatively or additionally increase the digestibility of the cereal-based feed Further the inclusion of the xylanase may additionally or alternatively increase the rate of bodyweight gam in an animal per unit amount of feed which the animal consumes In another embodiment, the xylanases of the present invention have applications in enhancing the de gnification and/or the bleaching of pulp according to art-recognized techniques The process compnses contacting the pulp with whole supematant xylanase, or one or more of the above descπbed punfied xylanases and is dependent upon factors such as pH temperature, treatment time, dosage of enzyme and the quantity and type of pulp It is preferred that the above process be earned out at a temperature and pH which will enhance the enzymatic activity Temperatures may range from approximately 50-90°C with 70-

— o —

85°C being preferred The preferred pH for the process ranges from about 5-11 preferably from about , most preferred above 7 to about 9 It is characteπstic for the puπfied xylanases of the present invention to be active over a wide alkaline pH-range as well as having high activity at the preferred pH range of about 7 to about 9 The preferred treatment peπod for applying the puπfied xylanases of the present invention is from about 30 minutes to about 4 hours depending upon factors such as the results desired, the quantity and quality of pulp treated and concentration of enzyme, for example

A suitable enzyme dosing is about 0 10 to 200 units/g of dry pulp more preferably 0 50 to 50 units/g The xylanase activity of the enzyme preparations is determined as follows To 1 8 ml of xylan solution (06% Sigma No X-0627, prepared in 0 05 M sodium acetate buffer and adjusted to pH 5 3 with acetic acid), 0 200 ml of suitably diluted enzyme in the same buffer is ' added The solution is incubated at 40°C for exactly 30 minutes The reaction is then stopped by adding 3 ml DNS reagent (3,5-dιnιtrosalιcylate 10g/l Na K tartrate 300g/l), and the color is developed by boiling the sample for 5 minutes The absorbency is then measured at a wave length of 540 nm One enzyme unit liberates one micromole of reducing sugars calculated as xylose per minute under assay conditions The activity is calculated from an enzyme dilution liberating 4 micromoles of reducing sugar under assay conditions

The present invention may be applied to upgrade or assist in the upgrading of any of a wide vaπety of processed pulps, i e , pulps which have been already previously treated in any of a vaπety of ways to reduce their lignin content and are treated in the process according to the invention to further enhance the lignm removal by chemical methods The present invention may be applied to treat hardwood and softwood kraft pulps to enhance lignm removal and bnghtenmg of the pulps The invention is particularly applicable to chemical pulps, i e , those in which the lignin component has been chemically modified by various chemical treatments such as in the sulfate (kraft) processes and oxygen delignifieation, and is preferably applied to kraft pulps In a preferred method, the enzymes of the present invention are applied to the pulp after kraft digestion or oxygen delignifieation but pπor to bleaching In the case where both kraft digestion and oxygen delignifieation are performed on the same pulp, the enzyme is applied after kraft digestion, pπor to oxygen delignifieation or after oxygen delignifieation The present invention is also applicable to ozone bleached pulps

The resulting pulp is treated to remove the releasable lignin component using an appropnate extractant In another embodiment, pulp treated with the enzymes of the present invention may be subsequently treated with lignin-degrading chemicals such as chloπne, chloπne dioxide and peroxide, and further extracted with an appropnate extractant In yet another embodiment, the enzyme treated pulp may be treated with an appropnate extractant, followed by lignin degradation and a final treatment with an appropnate extractant Such extractants

essentially solubilize the affected lignin component and suitable extractants include but are not limited to bases such as alkali metal hydroxides (E), DMF, dioxane, acetone, and alcohol Hydroxide extractions may be combined with hydrogen peroxide (E _p ) or oxygen (E _o ) The resulting pulp may then be further bleached by a chemical bleaching sequence such as chloπne dioxide (DED) or peroxide (P-P) to the desired bπghtness whereby substantial savings of chemicals are observed when compared to pulp bleached to the same brightness by the same sequence but without using the enzyme treatment Reduction of ehlonne containing chemicals or peroxide is achieved in such a way In addition, by performing the present invention with the above presented enzymes, one may apply the same amount of bleaching chemicals to the pulp and yet achieve a greater bnghtness in the treated pulp

In another embodiment, the present invention provides for additional applications of the punfied enzymes described above or whole xylanase supernatant containing xylanases according to the present invention in a vanety of industπal settings For example, the puπfied xylanases or whole xylanase supernatant may be used to enzymatically breakdown agricultural wastes for production of alcohol fuels and other important industπal chemicals or as a component in a detergent composition

EXAMPLES Example 1 Purification of Acidothermus Xylanase

Acidothermus cellulolyticus ATCC 43068 was obtained from the American Type Culture Collection in Rockville Md A culture filtrate was obtained by the culturing of the strain in a medium containing Henssen media (Henssen medium (g/L) K2HPO4 0 2 g MgSo4 7H20 0 3 g

CaCO3 0 2 g

FeSo4 7H2O 0 005 g

Yeast extract 0 1 g

Casamino acid 0 1 g NH4H03 0 2 g

Urea 0 1 g

Asparagine 0 25 g

Casein 0 2 g pH 5 5 with the addition of oat spelt xylan (1 %) at a pH of 5 5 and a temperature of 55-60 ^* C in a 250 ml Erlenmeyer flask at 100 rpm, for 6-8 days The culture supernatant was subjected to

ultrafiltration to concentrate the supernatant including extra cellular xylanase enzyme with the pellet discarded As described below, the supernatant included significant xylanase activity

Example 2 Determination of Characteristics of Acidothermus Xylanase

Purified xylanase obtained as described above in Example 2 was used to determine the characteristics of the xylanase

MOLECULAR WEIGHT Culture supernatant containing xylanase activity was concentrated 4X using

Centπprep 3 ultrafiltration cells (Amicon as per manufacturer instructions) Using a Pharmacia FPLC system, 1 ml concentrated material was applied to two gel filtration columns linked in tandem (Pharmacia Superdex G-200 10/30 followed by Pharmacia Superdex G-75 10/30) which had been equilibrated with 100 mM NaCI-50 mM citrate/phosphate buffer, pH 6 0 Flow rate was 0 5 ml/mm , UV absorption was monitored at 280 nm, 1 ml fractions were collected

Fractions were assayed for xylanase activity as follows The presence of xylanase was determined using a remazol brilliant blue dyed birchwood xylan (RBB-xylan Megazyme Australia) substrate 50 ul samples are mixed with 400 ul of substrate solution (1 25 % [w/v] RBB-xylan in 50 mM sodium acetate, pH 4 5) and incubated at 40 °C for 10 minutes Undigested xylan is precipitated by the addition of 1 ml 95% ethanol and removed by centrifugation Released dye remaining in solution is quantified by spectrophotometry (OD ₅₉₀ ) and is proportional to xylanase activity Activity may be quantified using a standard curve and is reported as XAU/ml (xylanase activity units per milliliter) Xylanase activity was found to elute after 42 minutes using this system Pharmacia low molecular weight gel filtration standards (1 25 mg/ml) were applied to the system using the above conditions and elution results were used to create a molecular weight standard curve Elution of Acidothermus xylanase corresponded to a molecular weight between 50-55 kilodaltons (approx 52 9 kilodaltons) when compared to the standard curve

ISOELECTRIC POINT

A gel overlay method was used to determine the isoelectπc point (pl) of Acidothermus xylanase Isoelectπc focusing (IEF) of culture supernatant containing xylanase activity was earned out using a PhastSystem (Pharmacia) as per manufacturer's instructions IEF gels pH 3-9 were overlaid with a melted agarose-substrate suspension (0 4 % (w/v) agarose 7 mg/ml RBB-xylan 0 5 % (v/v) glycerol in 50 mM sodium acetate, pH 4 5) and incubated at 37°C After 1 hour

xylanase activity was evident as a eleaπng zone Gels were allowed to dry completely and stored Xylanase pl was determined by comparison with identically run IEF gels containing silver stained pl markers (broad pl kit pH 3 5-9 3, Pharmacia Biotech) Visualization of proteins was by PhastSystem development silver staining, as per instructions

DH AND TEMPERATURE PROFILE

Enzyme samples were assayed using the RBB-xylan assay as described above in this Example The pH profile of the purified xylanase was determined by carrying out the RBB assay at pH's of 3 0, 4 0, 5 0, 6 0, 6 0 and 7 0 As shown in Figure 2, the purified xylanase has a pH optimum under the conditions of the assay of about 3 6-4 2

Temperature profile of the xylanase was determined by carrying out the RBB-xylan assay at pH 4 5 and a temperature of 37°C, 55°C, 65°C, 70°C and 80°C for a period of 10 minutes As shown in Figure 1 , the purified xylanase has an optimum temperature under the conditions of the assay of between about 70-80°C

THERMOSTABILITY

Separate samples of purified xylanase were incubated at temperatures of 70 ' C, 75 ' C, 80 ^' C, 85 ^■ C or 90 ^* C Aliquots were taken at certain time intervals to determine the activity of the xylanase after a given time of incubation at the given temperature The aliquots were assayed for activity according to the RBB-xylan assay at 60 ^* C, pH 4 5 and a time of 10 minutes and the half-life of the xylanase at the incubation temperatures calculated Results are shown in Figure 2, half lives at 70°C and 75°C under the conditions of the experiment were greater than 24 hours

LOW pH STABILITY

A purified sample of xylanase as described in Example 2 was adjusted to a pH of 3 3 with sodium hydroxide and incubated at RT The activity of the sample was measured at 30, 60, 90 and 120 minutes using the RBB assay descπbed above at 65 C, pH of 4 5 for 10 minutes As shown in Figure 4, a significant portion of the activity of the xylanase remained after 2 hours at low pH

Example 3

Treatment of Animal Feed With Acidothermus Xylanase The assay used for xylanase activity was an in vitro viscosity-reducing assay using wheat arabinoxylan as a viscous substrate under conditions which mimic those found in the Gl

tract of an animal Such an in vitro assay acts as a guide as to whether a xylanase (or mixture of xylanases) would have the desired effect of reducing digesta viscosity if used as a supplement in an animal feed. Activity was determined as follows.

One unit of xylanase activity is the amount of enzyme which liberates one μmol of reducing sugars (expressed as xylose equivalents) from the substrate in one minute under the conditions described

Reagents

1. 1% (w/v) xylan substrate Add 10 ml of 0.5 M sodium hydroxide to 1.0 g of xylan (Fluka 95590) Mix for 30 minutes with a magnetic stirrer Add about 40 ml of 0 05 M sodium acetate buffer, pH 6.5 Adjust pH to 6 5 with 1 M acetic acid Fill to 100 ml with 0 05 M sodium acetate buffer, pH 6.5 Substrate should be mixed all the time when used

2. 1 M acetic acid

Pipette 5.7 ml of glacial acetic acid into a volumetric flask and fill to 100 ml with distilled water.

3. 0.05 M sodium acetate buffer, pH 6.5 A. Dissolve 4 1 g of sodium acetate in distilled water and fill to 1000 ml with distilled water. B. Dissolve 3.0 g of glacial acetic acid in distilled water and fill to 1000 ml with distilled water. Adjust the pH of solution A to pH 6.5 with solution B

4. Dinitrosalicylic acid (DNS) reagent

Suspend 20.0 g of 3,5-dinιtrosalicylιc acid in about 800 ml of distilled water Add gradually 300 ml of sodium hydroxide solution (32 0 g NaOH in 300 ml of distilled water) while stirring continuously Warm the suspension in a water bath (the temperature may not exceed +48°C) while stirring until the solution is clear Add gradually 600 g of potassium sodium tartrate. Warm the solution (the temperature may not exceed +48°C) if needed until the solution is clear

Fill to 2000 ml with distilled water and filter through a coarse sintered glass filter

Store in a dark bottle at room temperature The Reagent is stable for a maximum of 6 months

Procedure 1 Enzyme sample

1 ml of enzyme dilution (in 0 05 M sodium acetate buffer, pH 6 5) is equilibrated at +50°C Add 1 ml of xylan substrate, stir and incubate at +50°C for exactly 30 minutes Add 3 ml of DNS-reagent, stir and boil the reaction mixture for exactly 5 minutes Cool the reaction mixture in a cold water bath to room temperature and measure the absorbance at 540 nm against distilled water

Enzyme blank

Incubate 1 ml of xylan substrate at +50°C for 30 minutes Add 3 ml of DNS-solution and stir Add 1 ml of enzyme dilution (in 0 05 M sodium acetate buffer pH 6 5) and stir Boil the mixture for exactly 5 minutes Cool the reaction mixture in a cold water bath to room temperature and measure the absorbance at 540 nm against distilled water

The absorbance difference between the enzyme sample and enzyme blank should be 0 3-0 5

Standard curve

Prepare standard solutions from anhydrous xylose in 0 05 M sodium acetate buffer pH 6 5 Xylose concentration in the standards should be 0 05-0 5 mg/ml Pipette 1 ml of standard solution, 1 ml of xylan substrate and 3 ml of DNS-reagent into a test tube Stir and boil for exactly 5 minutes Cool in a cold water bath to room temperature and measure the absorbance at 540 nm against standard blank In the standard blank, xylose solution is replaced by 1 ml of 0 05 M sodium acetate buffer pH 6 5 Otherwise standard blank is treated like xylose standard

Plot xylose concentration as a function of absorbance New standard curve is prepared for every new DNS-reagent

Calculation

The xylanase activity of the sample is calculated according to the following equation

Activity (U/g) = (\A(X) - A(Q)1 x k + C ) x 1000 x Df MW _xy , x t wherein:

A(X) = absorbance of the enzyme sample

A(O) = absorbance of the enzyme blank k = the slope of the standard curve

C« = the intercept of xylose standard curve

1000 = factor, mmol -> μmol

Df = dilution factor (ml/g)

MW _xy i = molecular weight of xylose (150 13 mg/mmol) t = reaction time (30 minutes)

The viscosity-reducing assay used to measure the ability of a xylanase to reduce viscosity was carried out as follows. The assay is carried out in all cases in duplicate

The xylanase enzyme to be assayed is diluted with 0 1 M Na-phosphate buffer having a pH of 6.5 in order to adjust the xylanase concentration so that the resulting solution possesses a xylanase activity of 1 0 unit per ml. Such xylanase activity is determined according to the assay method for xylanase activity descπbed in detail above

100 μl of the enzyme solution was added to 400 μl of a solution of wheat arabinoxylan (obtained from Megazyme Pty) in 0.1 M Na-phosphate at pH 6 5 in a glass test tube so that the final concentration of enzyme in the resulting solution was 0 2 U/ml and that of the wheat arabinoxylan was 1.0% w/w.

The test tubes containing the solutions were then sealed and placed in a water-bath set at 95°C for a certain period of time, typically 1 minute or 5 minutes After this heat treatment, the test tubes were cooled in an ice-water bath The viscosity of the rest' ng solution was measured at a temperature of 40°C using a Brookfield DV-II, CP 40 jmeter programmed to measure viscosity once a second. The figures shown in Table 1 are viscosity measurements after 20 minutes of incubation Xylanase from Acidothermus cellulolyticus was compared with xylanase from Aspergillus niger and Tnchoderma vmde, two well known additives for feed The results were as follows

15

TABLE 1

Xylanase Source Viscosity - (Pa.s) Viscosity (Pa.s) 20 Viscosity (Pa.S) 20 no heat treatment minutes after minutes after (Control) exposure to 95°C exposure to 95°C for 1 minute for 5 minutes

Trichoderma viride 2.0 x 10 ^'3 1.1 x 10 ^"z 1 1 x 10 ^' "

Aspergillus niger 1.4 x 10 ^"3 7.2 x 10 ^_J 7 3 x 10 ^"3

Acidothermus 4.3 x 10 ^"3 4.0 x 10 ^"J 9 9 x 10 ^"J cellulolyticus

As shown in Table 1 , exposure to a temperature of 95°C for one minute resulted in essentially no increase in the viscosity level with xylanase derived from Acidothermus cellulolyticus, while significant increases in viscosity were shown with the xylanases from Aspergillus niger and Trichoderma viride. Similarly, the increase in viscosity after exposure to a temperature of 95°C for five minutes of xylanase from Acidothermus cellulolyticus was less than half of that of the xylanases derived from Aspergillus niger and Tnchoderma vinde

Of course, it should be understood that a wide range of changes and modifications can be made to the preferred embodiments described above It is therefore intended to be understood that it is the following claims, including all equivalents, which define the scope of the invention.