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 MEP 2 18 is a native isolate with a broad spectrum of antifungal activity against plant pathogenic fungi. The ability of strain MEP 2 18 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 MEP 2 18. Among the C and N sources and C to N ratios tested, glucose and NH 4 NO 3 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 MEP 2 18, 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 MEP 2 18. 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 MEP 2 18 are potential candidates for controlling bacterial spot disease in tomato and pepper.