A novel strain of Bacillus amyloliquefaciens displaying broad spectrum antifungal activity and its underlying mechanism

One isolate among the various bacterial soil isolates screened in our study showed broad spectrum and profound antifungal activity and was characterized by biochemical and molecular approaches. Sequence analysis of the 16S rRNA gene indicated more than 98 % sequence similarity with Bacillus amyloliquefaciens ATCC 23350(T) and its variant Bacillus velezensis BCRC 17467(T). However, the biochemical characteristics of the isolated strain, such as cellular fatty acid composition, differed significantly from those of these two Bacillus strains, with the isolated strain containing anteiso-C15:0 (terminally branched saturated fatty acids) as a predominant fatty acid. The band pattern of the pulsed field gel electrophoresis profile of AvrII-digested genomic DNA of the isolate also showed significant variation from those of the two closely related Bacillus type strains. Based on these differences, the isolate was considered to be a new strain of B. amyloliquefaciens and deposited as Bacillus amyloliquefaciens strain fiply 3A in the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ) culture collection (DSM 22646) and in MTCC, IMTECH, Chandigarh (DSM 22646). Purification of the extracellular antifungal compound produced by the isolate by HPLC and its analysis by LC-ESI-MS revealed it to be a bacillomycin D-like cyclic lipopeptide. The antifungal activity of the compound was found to be due to its inhibitory effect on beta-1,3-glucan biosynthesis, a major fungal cell-wall component. Thus, we describe here the identification and characterization of a novel strain of Bacillus amyloliquefaciens (fiply 3A) which produces antifungal lipopeptide and the deciphering of its mechanism of action.