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.