A 3-deazauracil-resistant mutant of Bacillus subtilis with increased production of cytidine.

Bacillus subtilis No. 344 is a cytidine-producing mutant strain derived from wild type strain No. 122. When 3-deazauracil-resistant mutants were derived from strain No. 344, some of the mutants had higher productivities of cytidine. Among them, strain No. 428 accumulated 14.2 mg/ml cytidine in the culture. Cytidine 5'-triphosphate (CTP) synthetase from strain No. 428 changed to be free from feedback inhibition by CTP, compared with the enzyme from strain No. 344.