Isolation and partial chemical characterization of an antimicrobial peptide produced by a strain of Bacillus subtilis

An antimicrobial lipopeptide has been isolated, purified to homogeneity, and partially characterized from a strain of Bacillus subtilis found in apple fruit. The compound consists of an acidic peptide containing aspartic acid, glutamic acid, serine, glycine, alanine, proline, valine, and leucine in a ratio of 2:3:1:1:1:1:1:4,. The infrared spectrum indicates that the peptide antibiotic contains an acyl chain and has a lactone bond in its structure. On the basis of amino acid analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and gel filtration data, the molecule has a molecular mass of 1.5 kDa but also forms aggregates in excess of 20 kDa. The peptide antibiotic appears to be similar to a number of lipopeptide antibiotics often termed "biosurfactants" and classified as fatty acid-containing peptolides. The antibiotic demonstrates a broad spectrum of activity against Gram-negative bacteria, shows little activity against Gram-positive organisms, and is active against one of the two fungi assayed.