Screening of cytidine-producing mutants based on feedback-inhibition resistance of CTP synthetase

Aim ：To obtain a mutant which could increase the yield of cytidine by decreasing the feedback-inhibition of CTP synthetase. Methods ：A cytidine deaminase deficient strain was induced mutation by nitrosoguanidine（NTG） and screened with pyrimidine analogs，to obtain 6-azauracil，5-fluorocytidine and 3-deazauracil resistant strains. Results ：A mutant of Bacillus subtilis K-215 was obtained，with the critical resistance concentration to 6-azauracil，5-fluorocytidine and 3-deazauracil being 0.9，3.5 and 4.5 mg/mL，respectively.The CTP synthetase activity of the mutant was increased by 5.2 fold and cytidine was accumulated to 6.2 mg/mL after 72 h fermentation at 37 ℃. Conclusion ：The mutant K-215 has higher cytidine productivity and is partially free from the feedback-inhibition on CTP synthetase.