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Surface-active properties of two classes of Bacillus subtilis S499 lipopeptides, surfactins and iturins A, were studied. These lipopeptides were purified until molecules with unique lipidic structure were obtained. Then, adsorption kinetics and monolayer properties at the air-water interface, micelle forming capacity in aqueous solution, and foaming properties for both homologous lipopeptides and mixtures of main components, were characterised. Lipopeptide interfacial behaviour depends on lipophilic moiety structure, concentration, and presence of NaCl in solution. Diffusion coefficients of lipopeptides having lipidic chain with 13 to 15 carbon atoms were equivalent to those of classical surfactants. Increasing the lipidic chain length over 15 carbon atoms decreased the diffusion coefficient. The addition of NaCl 0.1M in solution induced similar effect. When the concentration exceeded a critical value, the surfactin adsorption rate decreased with increasing the lipidic chain hydrophobicity. Monolayer study in compression showed the importance of lipidic part on molecule orientation and film stability, especially for iturin A. Micelle forming capacity also increased with the lipidic chain length. Lipopeptides with lipidic chain of 14 and 15 carbon atoms efficiently formed and stabilised foam with moderate density but constituted with fine bubbles. Therefore, they appeared as excellent foaming agents. Surfactin produced foam with higher density but less stable than iturin A. The optimal structure for these properties was formed by a lipophile part with 14 carbon atoms. Mixtures of surfactin and iturin A having lipidic chain of 15 carbon atoms showed synergistic effects on adsorption properties, film stability, foam density and foam stability. These effects specifically appeared with a surfactin-iturin A mixture in a proportion 40 : 60.

Bacillus subtilis --- Surfactants --- peptides --- Lipids --- Foams --- Rheological properties --- Surfactine --- Iturine

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Emulsions. --- Emulsions --- Bacillus subtilis --- peptides --- lipoproteins --- chemicophysical properties --- Additives --- essential oils --- formulations --- Thermodynamique --- Surfactine --- Iturine

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Cassava. --- Cassava --- Cassava mosaic virus --- Disease control --- Chemical control --- Virazole --- Surfactine --- Rwanda

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In this study, the influence of physiological conditions on lipopeptide synthesis by B. subtilis was considered for quantitative and qualitative optimizations of the production of these molecules. Concerning quantitative optimization, only the effect of oxygen transfer was studied. B. subtilis S499 and AGH2 cultures were performed in various media either in flasks with different culture volumes and therefore different oxygen transfer 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 transfer had no effect in minimal media but enhanced biomass and total lipopeptide productions in rich media. However, production of these antibiotics per cell diminishes 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 B. 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. B. 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.

Bacillus subtilis --- peptides --- lipoproteins --- Biosynthesis --- Surfactants --- biological properties --- culture media --- Extraction --- Iturine --- Surfactine --- Fengycine

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Structure activity relationships --- Biophysics --- membranes --- Antimicrobials --- chemical structure --- Molecular biology --- Interface phenomena --- Surfactine --- Fengycine