IMPROVEMENT OF A CYTIDINE-PRODUCING MUTANT OF BACILLUS-SUBTILIS INTRODUCING A MUTATION BY HOMOLOGOUS RECOMBINATION

Bacillus subtilis No. 428 is a cytidine-producing mutant strain derived from wild-type strain No. 122. To identify the rate-determining factor for production of cytidine by strain No. 428, we examined the properties of the strain. We found that carbamyl phosphate synthetase P (CPSase P) from strain No. 428 was sensitive to feedback inhibition by uridine S-monophosphate (UMP), and therefore, this enzyme reaction was the rate-determining step for cytidine production, Thus, we introduced a mutation causing lack of feedback inhibition of CPSase P into the CPSase P-deficient mutant of strain No. 428 by homologous recombination. Some of the transformants had higher productivity of cytidine, Among them, strain No. 515 produced 18.8 mg/ml cytidine in the culture, CPSase P from strain No. 515 was freed from feedback inhibition by UMP, having obtained the characteristic of the donor.