Identifications of Surfactin-Type Biosurfactants Produced by Bacillus Species Isolated from Rhizosphere of Vegetables

Abstract

Surfactins are cyclic lipopeptides consisting of a β-hydroxy fatty acid of variable 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 <i>Bacillus</i> species and are well regarded for their antibacterial, antifungal, and antiviral activities. For their surfactin production profiling, several <i>Bacillus</i> strains isolated from vegetable rhizospheres were identified by their fatty acid methyl ester profiles and were tested against phytopathogen bacteria and fungi. The isolates showed significant inhibition against of <i>E. amylovora</i>, <i>X. campestris</i>, <i>B. cinerea</i>, and <i>F. culmorum</i> and caused moderate effects on <i>P. syringae</i>, <i>E. carotovora</i>, <i>A. tumefaciens</i>, <i>F. graminearum</i>, <i>F. solani</i>, and <i>C. gloeosporioides</i>. Then, an HPLC-HESI-MS/MS method was applied to simultaneously carry out the quantitative and in-depth qualitative characterisations on the extracted ferment broths. More than half of the examined <i>Bacillus</i> strains produced surfactin, and the MS/MS spectra analyses of their sodiated precursor ions revealed a total of 29 surfactin variants and homologues, some of them with an extremely large number of peaks with different retention times, suggesting a large number of variations in the branching of their fatty acid chains.