Improvement of FK506 production by selection of 4-Aminobutyric acid-tolerant mutant and optimization of its fermentation using response surface methodology

Tacrolimus (FK506), a 23-membered polyketide macrolide with immunosuppressant activity, can be produced by Streptomyces tsukubaensis. We studied a variety of mutant strains of S. tsukubaensis for the microbial production of FK506. The best strain (CZ-19) was obtained from the parent strain LLZ-1 by nitrosoguanidine mutation and 4-Aminobutyric acid (FK506 precursor structure analogs) adaption. In the shake-flask experiments, titer of FK506 by CZ-19 was 532.44 mg/L, increased by 65.13% compared to that of the parent strain. Through single factor experiments and response surface methodology, we further optimized the medium for improved FK506 production by CZ-19 in shake flask culture. The optimal medium for enhanced FK506 production was as follows: 17.19 g/L corn starch, 21.78 g/L glucose, 8.06 g/L peptone, and 18.98 mg/L 4-aminobutyric acid. The predicted FK506 titer was 906.49 mg/L, and the experimental data confirmed the validity of the model. The present study demonstrates that S. tsukubaensis CZ-19 is a promising strain for industrial production of FK506.