[Metabolic engineering of for thymidine production].

Thymidine, as a crucial precursor of anti-AIDS drugs (e.g., zidovudine and stavudine), has wide application potential in the pharmaceutical industry. In this study, we introduced the thymidine biosynthesis pathway into the wild-type MG1655 by systems metabolic engineering to improve the thymidine production in . . Firstly, , , , , , and were successively deleted to block the thymidine degradation pathway and salvage pathway in the wild-type . MG1655. Then, the pyrimidine nucleoside operons from F126 were introduced to enlarge the metabolic flux of the uridylic acid synthesis pathway. Finally, the expression of uridylate kinase, ribonucleoside diphosphate reductase, thymidine synthase, and 5'-nucleotidase in the thymidine biosynthesis pathway was optimized to enhance the metabolic flux from uridylic acid to thymidine. The engineered THY6-2 strain produced 11.10 g/L thymidine in a 5 L bioreactor with a yield of 0.04 g/g glucose and productivity of 0.23 g/(L·h). In this study, we constructed a strain that used glucose as the only carbon source for efficient production of thymidine and did not harbor plasmids, which provided a reference for the research on other pyrimidine nucleosides.