PURPOSE: To enable mass-production of cytidine by transforming a specific microorganism with a recombinant DNA containing a cytidine triphosphate synthetase(CTP synthetase) gene and culturing the transformant.

CONSTITUTION: Bacillus natto C-1 strain (A) capable of producing cytidine and having the following bacteriological properties is separated from soil. The shape and size of the cell, bacillus, (0.7-1.0)×(2-8)μm; Gram-positive; reducing nitric acid salt; hydrolyzing starch; etc. The cell of the strain A is extracted and cloned to obtain a CTP synthetase gene (B). The component B is introduced into a vector and the strain A is transformed with the resultant recombinant DNA (C) (e.g. plasmid pFS037) to obtain a recombinant (D). Cytidine is produced by inoculating the strain D on a medium containing glucose, tetracycline, etc., and culturing at about 37°C for about 3 days.