The first report of antifungal lipopeptide production by a Bacillus subtilis subsp. inaquosorum strain

A strain of bacteria in the Bacillus subtilis species complex was isolated from a building's air vent in the Washington DC area, USA, and produced strong antifungal activity with in vitro assays. This strain, designated (HU Biol-II), showed pronounced inhibitory effects on mycelial growth of a wide spectrum of fungi. The objectives of this study were to use genome sequencing to confirm the taxonomy of HU Biol-II, evaluate its antifungal activity and implement genome mining and HPLC-MS/MS to characterize the bioactive secondary metabolites. The strain, as determined by multilocus sequence alignment analysis, was identified as a member of Bacillus subtilis subsp. inaquosorum clade. Core genome phylogeny showed that the isolate is most closely related to B. subtilis subsp. inaquosorum strain DE111, a commercially produced human probiotic. The investigation identified eight bioactive metabolite clusters in the genome. HPLC MS/MS was able to confirm the production of seven of the metabolites. This study is the first to report the production of two antifungal cyclic lipopeptides (bacillomycin F and fengycin) from a member of B. subtilis subsp. inaquosorum. The strain also produced the antibacterial aurantinin B, which confirms the biosynthetic cluster responsible for its production. Comparative genomics and metabolomics demonstrated the commercial probiotic strain DE111 produced the same metabolites, with the exception of aurantinin B. These findings are the first description of the secondary metabolites produced by a strain of B. subtilis subsp. inaquosorum.