Structural analysis of Bacillus licheniformis 86 surfactant.

A tentative structure and composition of a surfactant, BL-86, produced by Bacillus licheniformis 86 is described. The surfactant is a mixture of lipopeptides with the major components ranging in size from 979 to 1091 Da and varying in increments of 14 Da. The variation in molecular weight represents changes in the number of methylene groups in the lipid and/or peptide portion of the surfactant. There are 7 amino acids per molecule. The peptide portion is composed of the following amino acids: glutamic acid or glutamine (glx), aspartic acid or asparagine (asx), valine, leucine, and isoleucine at a ratio of 1.0:1.0:1.4:3.0:0.6, respectively. The leucine is present as both the D and L isomers at a ratio of about 2:1, respectively. Forty percent of the molecules contain L-valine instead of L-isoleucine. The glx and asx are present as a combination of L-glutamic acid and L-asparagine and/or L-glutamine and L-aspartic acid. The N-terminus of the peptide is blocked, most likely by a peptide bond to the lipid portion. An ester carbonyl structure is present, which could be a part of a lactone ring connecting the beta position of the lipid to one of the carbonyl groups in the peptide. The lipid portion is composed of, on average, 8-9 methylene groups, and contains a mixture of linear and branched tails. Results of DCI-MS and FAB-MS analyses, as well as surface tension measurements, of purified BL-86 HPLC fractions support the proposed composition.