Study of the influence of physiological conditions on Bacillus subtilis lipopeptide biosynthesis | Etude de l'influence des conditions physiologiques sur la biosynthese des lipopeptides chez Bacillus subtilis

In this study, the influence of physiological conditions on lipopeptide synthesis by Bacillus subtilis was considered for quantitative and qualitative optimizations of the production of these molecules. Concerning quantitative optimization, only the effect of oxygen transfert was studied. Bacillus subtilis S499 and AGH2 cultures were performed in various media either in flasks with different culture volumes and therefore different oxygen transfert conditions, or in fermentors with aeration rates of 0,05 vvm, 0,2 vvm and 0,5 vvm. Some fermentations were performed with pure oxygen. The results show that improved oxygen transfert had no effect in minimal media but enhanced biomass and total lipopeptide productions in rich media. However, production of these antibiotics per cell diminish with the increase of aeration. Qualitative optimization was focused on research of conditions for production of few number of homologous compounds in order to reduce purification cost due to diversity of lipopeptides homologs and families produced by Bacillus subtilis. Three strategies were adopted: strain screening, addition of alpha-amino acids, addition of short and long chain fatty acids to culture media. The intensity and number of homologs produced depend on strains and culture media. Bacillus subtilis NT02 presented an original production profile. It produced various bacillomycin L homologs when cultivated in Landy medium, but primarily one homologous compound (C15) when cultivated in optimized medium. Amino acid addition modifies homolog proportions but not their number. Short chain fatty acid addition has no convincing effect on bacillomycin L homolog profile; however a relation exists between cellular fatty acid proportions and these homologs. Unlikely, long chain fatty acids (C15 to C18) are directly incorporated in cellular fatty acids but not in produced lipopeptides