To improve fermentative production of enduracidin, heavy‐ion beams generated by the Heavy Ion Research Facility in Lanzhou (HIRFL), China, were employed for the first time to generate mutations in Streptomyces fungicidicus. Initial screening detected 44 positive mutants with larger inhibition zone, which were subsequently tested based on flask fermentation. Finally, 20 mutants showed 20% increase in enduracidin production, when compared with the original strain. Among them, enduracidin production by the three mutants (M13, M30, and M34) was significantly higher than that by the original strain. In particular, mutant M30 exhibited highest enduracidin production, which was 114% higher than that obtained with the original strain. Following culture optimization, the maximal enduracidin yield obtained by M30 reached 918.5 mg/L in 10 days, which was 34% higher than that noted in the control.

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BACKGROUND High‐efficiency utilization of sweet sorghum juice can bring significant economic feasibility of l‐lactic acid production. However, an expensive nitrogen source increases the capital cost, and the complex composition of sweet sorghum juice could limit the yield. RESULTS In the present study, a bioprocess was developed to enhance the efficiency of l‐lactic acid production using purified sweet sorghum juice and cheap nitrogen supply strategies. It was first demonstrated that cheaper soybean hydrolysate could be used as a low‐cost nitrogen source for efficient l‐lactic acid production by Lactobacillus thermophilus A69, the optimal soybean hydrolysate concentration being 25 g L−1. It was then proved that the efficiency of l‐lactic acid production was significantly boosted using sweet sorghum juice purified via clarification treatment. Finally, on combining the cheap nitrogen source and the clarification strategy, 114.6 g L−1 l‐lactic acid with a productivity of 2.61 g L−1 h−1 was produced by A69 strain in a 5 L bioreactor. CONCLUSION This study provides a simple, practical and economic approach to promote l‐lactic acid production using sweet sorghum juice as feedstock. © 2019 Society of Chemical Industry