Abstract
Surfactins are cyclic lipopeptides consisting of a β-hydroxy fatty acid of various chain length and a peptide ring of seven amino acids linked together by a lactone bridge, forming the cyclic structure of the peptide chain. These compounds are produced mainly by Bacillus species and possess numerous biological effects such as antimicrobial (antiviral, antibacterial, and antifungal) activities. A mixture of surfactins extracted from Bacillus subtilis strain SZMC 6179J was examined by HPLC-ESI-IT-MS technique, enhancing their separation to reveal novel lipopeptide varieties with higher masses and to characterize their structures. During the MS2 spectra analyses of their sodiated molecular ions [M + Na]+, a previously rarely encountered group of surfactins was detected and two novel types of the group were discovered containing methyl esterified aspartic acid residue in their fifth amino acid position. The relative amounts of these monomethyl isoforms exceeded 35% of the produced surfactin in total. In the m/z value of 1114, all the detected isoforms possessed aspartic acid 4-methyl ester residue in their fifth amino acid position (C17-[Lxx4, AME5], C18-[AME5]), offering an opportunity to separate a pure fraction of the compound and to study its biological activities in the future.
Highlights
Surfactins are cyclic lipopeptide-type biosurfactants produced mainly by Bacillus subtilis, a Gram-positive bacterium [1]
Observing the results provided by the MS2 analyses of the sodiated surfactin molecules led us to the conclusion that the examined B. subtilis strain produced relatively high amounts of the different isoforms in total
Surfactin homologues extracted from the B. subtilis strain SZMC 6179J were identified by HPLC-ESI-IT-MS
Summary
Surfactins are cyclic lipopeptide-type biosurfactants produced mainly by Bacillus subtilis, a Gram-positive bacterium [1] It consists of a hydrophobic β-hydroxy fatty acid chain of various length (C12–C15) linked to a ring of seven amino acids (Figure 1). The length of the fatty acid chain and the amino acid sequence varies, resulting in numerous isoforms of the compound listed and characterized in previous works [2] (Table 1). Most of these variants were reported in the 1990s, a recent study from our group introducing a novel surfactin. Glu [Val2] surfactin [Ala4] surfactin [Leu4] surfactin [Ile4] surfactin [Ile2,4] surfactin [Val7] surfactin [Ile7] surfactin
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