A two-step ultrafiltration and liquid chromatography-electronic spray ionization-tandem mass spectrometry (LC-ESI-MS/MS) were applied to investigate the nature of lipopeptides in the methanol extract harvested from marine Bacillus megaterium. The structure of lipopeptide homologs were characterized by using collision-induced dissociation mass spectrometry analysis. Collectively, two kinds of linear fengycin A and B with a double bond were characterized for the first time besides the popular cyclic fengycin A and B with the difference in the amino acid at position 6 of the peptide moiety. It is worth noting that two kinds of linear isoforms of surfactins and two kinds of cyclic isoforms of esperin with a smaller peptide ring formed by the fifth L-Asp and β-hydroxy fatty acid were also separated and identified in addition to the all seven kinds of cyclic isoforms of surfactins. Only one analogue (bacillomycin D) of iturin family was identified in this research. To our best knowledge, this is the first report that more than 40 variants of lipopeptides from one strain of Bacillus were identified using our potent purification and identification methods.
Keywords: Bacillus megaterium; Identification; LC–ESI–MS; LC–ESI–MS/MS; Lipopeptide; Ultrafiltration.