A Novel Variant of Narrow-Spectrum Antifungal Bacterial Lipopeptides That Strongly Inhibit Ganoderma boninense

Abstract

Bacterial antifungal cyclic lipopeptides (ACLs) have become a promising alternative to synthetic fungicide to control pathogenic fungi. Bacillus sp. is known to produce three families of ACL, namely iturin, surfactin, and fengycin. In this paper, we characterized the ACLs produced by B. methylotrophicus HC51 (referred as HC51) mainly regarding its composition and effectivity against fungal plant pathogen. HC51 culture was tested against various pathogenic fungi and the ACLs were extracted and analyzed using liquid chromatography-electrospray ionization mass spectrometry. HC51 showed strong antifungal activity against the plant pathogens Ganoderma sp. and Fusarium sp. Cell-free methanol extract of HC51 contains iturin A and various variants of fengycin. C16 fengycin A was present in four fractions which indicates it as a major component of ACL from HC51. Five variants of fengycin were detected, four of which had been previously reported. We found a novel C17 fengycin F that is characterized by a substitution of L-ornithine into lysine. Considering that L-ornithine is an important building block of fengycin, this substitution suggests the possibility of an alternative pathway for fengycin biosynthesis.

Keywords: Antifungal lipopeptide; Bacillus methylotrophicus; Electrospray ionization mass spectrometry; Fengycin; Ganoderma boninense.