Cloning, reassembling and integration of the entire nikkomycin biosynthetic gene cluster into Streptomyces ansochromogenes lead to an improved nikkomycin production

BACKGROUND Nikkomycins are a group of peptidyl nucleoside antibiotics produced by Streptomyces ansochromogenes. They are competitive inhibitors of chitin synthase and show potent fungicidal, insecticidal, and acaricidal activities. Nikkomycin X and Z are the main components produced by S. ansochromogenes. Generation of a high-producing strain is crucial to scale up nikkomycins production for further clinical trials. RESULTS To increase the yields of nikkomycins, an additional copy of nikkomycin biosynthetic gene cluster (35 kb) was introduced into nikkomycin producing strain, S. ansochromogenes 7100. The gene cluster was first reassembled into an integrative plasmid by Red/ET technology combining with classic cloning methods and then the resulting plasmid(pNIK)was introduced into S. ansochromogenes by conjugal transfer. Introduction of pNIK led to enhanced production of nikkomycins (880 mg L(-1), 4 -fold nikkomycin X and 210 mg L(-1), 1.8-fold nikkomycin Z) in the resulting exconjugants comparing with the parent strain (220 mg L(-1) nikkomycin X and 120 mg L(-1) nikkomycin Z). The exconjugants are genetically stable in the absence of antibiotic resistance selection pressure. CONCLUSION A high nikkomycins producing strain (1100 mg L(-1) nikkomycins) was obtained by introduction of an extra nikkomycin biosynthetic gene cluster into the genome of S. ansochromogenes. The strategies presented here could be applicable to other bacteria to improve the yields of secondary metabolites.