Identification of cyclic lipopeptides produced by Bacillus vallismortis R2 and their antifungal activity against Alternaria alternata

Abstract

Aim: To identify the different antifungal biomolecules produced by isolate Bacillus vallismortis R2 and analyse their effect on Alternaria alternata, a common pathogen causing black point disease of wheat.

Methods and results: The different antifungal molecules produced by isolate R2 were purified by column chromatography. The liquid chromatography-mass spectrometry of purified fractions confirmed the ability of R2 to produce biomolecules putatively similar to three different families of cyclic lipopeptides (CLPs) viz. surfactins, iturins and fengycins. The synergistic interaction among CLPs was evident from significant increase in the antifungal activity of mixture of purified fractions as compared to that of the individual fractions by agar well diffusion assay. The evaluation of antifungal activity of purified fractions by 96-well microtitre plate assay showed that the fengycin-like molecules supported significantly higher antifungal activity against A. alternata than iturin A and no antifungal activity was supported by surfactin.

Conclusions: The isolate R2, producing different CLPs, can be used as an environmental friendly alternative to chemical fungicides. Among the three different CLPs viz. surfactin, iturin A and fengycin produced by R2, the fengycins were the most active lipopeptides.

Significance and impact of the study: This is the first report on co-production of three different types of CLPs by the cells of B. vallismortis.

Keywords: Bacillus vallismortis; antifungal activity; confocal microscopy; cyclic lipopeptides; membrane permeability.