Effects of heavy-ion beam irradiation on avermectin B1a and its analogues production by Streptomyces avermitilis

The biggest challenge in anabolism research is to improve the stability and safety of microbial metabolite production on an industrial scale. One class of metabolites, avermectins, are produced by Streptomyces avermitilis. In this study, an avermectin B1a-high-producing mutant was produced using heavy ion mutagenesis and selected based on LTQ-MS and HPLC-UV method. The mutants ZJAV-Y-147 and ZJAV-Y-HS, obtained after subjecting the spores of S. avermitilis to 70 Gy of C-12(6+) heavy ion irradiation, were found to best improve the avermectin B1a production (4822.23 mu g/mL and 4632.17 mu g/mL, respectively). These two mutants' yielded of avermectin B1a were 2-fold high than the original strains. The DNA of the original and mutant strains were analyzed by RAPD technique with four random primers after irradiated with ion beam irradiation. The results show that different high-titer S. avermitilis strains contain different genetic modifications. In addition, the mutation position, mutation type and sequence context of all mutations of aveC, aveD, aveI, aveR gene in two mutants S. avermitilis were researched, and the production of avermectin B1a and its analogues of wild-type and mutants were analyzed by fermenting 240 h, which was suggested that the partial base deletion of aveI gene may be the key sites for increasing avermectin B1a production after the C-12(6+)-ion irradiation. All these modifications promote increased avermectin biosynthesis, leading to multiple high-titer S.avermitilis strains. The results demonstrate that this is an effective approach to engineer S.avermitilis as a host for the biological production of commercial analogs.