Mutation breeding of high avermectin B1a-producing strain by the combination of high energy carbon heavy ion irradiation and sodium nitrite mutagenesis based on high throughput screening
Song, Xiaoqing | Zhang, Yun | Zhu, Xudong | Wang, Yonghong | Chu, Ju | Zhuang, Yingping
Microbial mutation breeding has been widely used because it is one of the most efficient and practical breeding strategies in the fermentation industry. However, different mutagenesis methods cause various degrees of DNA damage to individual microorganisms, which lead to diverse characteristics of the mutants. In this study, the effects of four different mutagenesis methods on the mutation breeding of Streptomyces avermitilis for improving avermectin B1a production were investigated with an optimized liquid microtiter plate (MTP) culture system. First, an effective and feasible MTP system for mutant strain screening was evaluated through the optimization of the oxygen transfer rate and rapid titer determination. Then, high energy carbon heavy ion irradiation, diethyl sulfate, ultraviolet- (UV) irradiation combined with lithium chloride, and sodium nitrite were used as the mutagens for mutation breeding, respectively. Results showed that carbon heavy ion irradiation had the advantages of possessing the highest positive mutation rate and mean-production of positive mutant strains in the first generation. Sodium nitrite treatment resulted in mutant strains with better inherited stability than the other three methods. Through the combined treatment of carbon heavy ion irradiation and sodium nitrite treatment, an inheritstable mutant S. avermitilis S-233 with high avermectin B₁ₐ production was successfully obtained. The fermentation verification in a 500-liter (L) bioreactor demonstrated that the avermectin B₁ₐ produced by mutant S. avermitilis S-233 reached 6818 μg/mL, which was 23.8% higher than that of parent strains.
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