Effect of metal ions on lipopeptide secretion from Bacillus subtilis strain FJAT-4: Negative regulation by Ca2+
Mei‐Chun Chen, Meixia Zheng, Yanping Chen, Rongfeng Xiao, Xuefang Zheng, Bo Liu, Jieping Wang, Yujing Zhu
Abstract
Abstract Aims This study aimed to investigate the effect of metal ions on lipopeptide production by Bacillus subtilis strain FJAT-4 and the mechanism of negative regulation by Ca2+. Methods and Results The quantitative measurement of lipopeptides in response to K+, Na+, Mg2+ and Ca2+ addition was carried out by LC-MS. The contents of fengycin and surfactin varied within the range of 116.24–129.80 mg/L and 34.03–63.11 mg/L in the culture media containing K+, Na+ and Mg2+, while the levels were 0.86 and 0.63 mg/L in the media containing Ca2+. Ca2+ at a high concentration (45 mM) did not adversely affect the growth of strain FJAT-4, but caused significant downregulation of lipopeptide synthesis-related gene expression, corresponding to a decrease in lipopeptide production. This inhibition by Ca2+ was further investigated by proteomic analysis. In total, 112 proteins were upregulated and 524 proteins were downregulated in the presence of additional Ca2+ (45 mM). Among these differentially expressed proteins (DEPs), 28 were related to phosphotransferase activity, and 42 were related to kinase activity. The proteomics results suggested that altered levels of three two-component signal-transduction systems (ResD/ResE, PhoP/PhoR and DegU/DegS) might be involved in the control of expression of the fen and srfA operons of FJAT-4 under high calcium stress. Conclusions The Ca2+ at the high concentration (45 mM) triggers a decrease in lipopeptide production, which might be attributed to the regulation of three two-component signal-transduction systems ResD/ResE, PhoP/PhoR and DegU/DegS. Significance and Impact of the Study The regulatory effect of calcium on the expression of genes encoding lipopeptide synthetases can be applied to optimize the production of lipopeptides.