Effect of heterogeneity of hydrophobic moieties on surface activity of lichenysin A, a lipopeptide biosurfactant from Bacillus licheniformis BAS50.

Lichenysin A, a surface-active lipopeptide produced by Bacillus licheniformis, strain BAS50, contains longchain beta-hydroxy fatty acids. Regulation of the synthesis of fatty acids and beta-hydroxy fatty acids was studied by modifying the culture medium. Addition of branched-chain alpha-amino acids to the medium caused similar changes to both cellular fatty acid and to beta-hydroxy fatty acid composition in the lipophilic part of lichenysin A. Production of lichenysin A was enhanced about two- and four-fold by addition of L-glutamic acid and L-asparagine respectively. It is suggested that these amino acids may be involved in the control of lipopeptide formation. Elucidation of the structure-function relationship of surface-active lipopeptides by analysis of the activities of structurally characterized compounds is discussed. Fractions of lichenysin A with branched beta-hydroxy acids in the lipid tail demonstrated lower surface-tension activity than the fractions of lichenysin A having straight beta-hydroxy acids. The presence of a lichenysin A fraction with beta-hydroxymyristic [(C14)n] acid residues appears to have an important influence on the surface activity of a mixture of lichenysins A.