Effect of metal ions on lipopeptide secretion from Bacillus subtilis strain FJAT-4: Negative regulation by Ca2+

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.