Improvement of biomass and cyclic lipopeptides production in Bacillus amyloliquefaciens MEP218 by modifying carbon and nitrogen sources and ratios of the culture media

Abstract

Bacillus amyloliquefaciens MEP218 is a native isolate with a broad spectrum of antifungal activity against plant pathogenic fungi. The ability of strain MEP218 to antagonize phytopathogens is due to the production of cyclic lipopeptides (CLPs). In this work, different carbon (C) and nitrogen (N) sources and C to N ratios were evaluated in order to improve both, biomass and CLPs production by strain MEP218. Among the C and N sources and C to N ratios tested, glucose and NH4NO3 at the C to N ratio of 10:1 enhanced significantly biomass and CLPs yield. Moreover, CLPs produced in this medium exhibited higher antibacterial activity against Xanthomonas axonopodis pv. vesicatoria (Xav) than those obtained in the recommended medium for CLPs production. Interestingly, CLPs addition influenced the development of Xav biofilm on biotic and abiotic surfaces. A comparison of HPLC-chromatograms of CLPs obtained in the optimized medium versus the ones obtained in the recommended medium showed a notable increase of surfactin in the CLPs obtained in the optimized medium. Furthermore, two peaks with antibacterial activity against Xav, identified by mass spectrometry analysis as fengycins A and B, were detected in the CLPs from the strain MEP218, grown in the optimized culture medium. The results obtained in this work suggest that changes in C and N sources and C to N ratios affect the yield and type of CLPs produced by B. amyloliquefaciens MEP218. To the best of our knowledge, this is the first study to report the finding of fengycins with antibacterial activity. CLPs produced by the strain MEP218 are potential candidates for controlling bacterial spot disease in tomato and pepper.