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

Surfactins are cyclic lipopeptides consisting of a beta-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 Bacillus species and are well regarded for their antibacterial, antifungal, and antiviral activities. For their surfactin production profiling, several Bacillus 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 E. amylovora, X. campestris, B. cinerea, and F. culmorum and caused moderate effects on P. syringae, E. carotovora, A. tumefaciens, F. graminearum, F. solani, and C. gloeosporioides. 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 Bacillus 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.

Automated summary

Surfactins are cyclic lipopeptides consisting of a beta-hydroxy fatty acid and a peptide ring. They have antibacterial, antifungal, and antiviral activities and can be produced by Bacillus species. Bacillus strains isolated from vegetable rhizospheres were identified and tested for surfactin production and inhibition on phytopathogen bacteria and fungi. An HPLC-HESI-MS/MS method was used for quantitative and qualitative analysis, revealing the production of 29 surfactin variants and homologues by more than half of the tested Bacillus strains.