The positive effects of Mn(2+) on nitrogen use and surfactin production by Bacillus subtilis ATCC 21332.

Surfactin, one of the most effective biosurfactants, has great potential in commercial applications. Studies on effective methods to reduce surfactin's production cost are always a hotspot in the research field of biosurfactants. The aim of this study was to reveal the role of Mn(2+) in promoting the biosynthesis of surfactin by Bacillus subtilis ATCC 21332, which could arise more targeted suggestions on surfactin yield promotion. In this study, B. subtilis was cultivated in media containing different Mn(2+) concentrations. The obtained results showed that the yield of surfactin gradually increased upon Mn(2+) addition (0.001 to 0.1 mmol/L) and achieved the maximal production of 1500 mg/L, which reached 6.2-fold of the yield obtained in media without Mn(2+) addition. Correspondingly, the usage ratios of ammonium nitrate were improved. When the Mn(2+) concentration was higher than 0.05 mmol/L, nitrate became the main nitrogen source, instead of ammonium, indicating that the nitrogen utilization pattern was also changed. An increase in nitrate reductase activity was observed and the increase upon Mn(2+) dosage had a positive correlate with nitrate use, and then stimulated secondary metabolic activity and surfactin synthesis. On the other hand, Mn(2+) enhanced the glutamate synthase activity, which increased nitrogen absorption and transformation and provided more free amino acids for surfactin synthesis.