Characterization of the antifungal activity of the bacterial isolate Bacillus velezensis TCG15.

Bacillus velezensis TCG15 is a bacterial isolate from soil that shows antifungal activity against Aspergillus spp. and Candida spp. This study aimed to characterize its antifungal activity. TCG15 produces cyclic lipopeptides (cLPs), including surfactin A, plipastatin, and bacillomycin L. We obtained the complete sequence of the operon encoding nonribosomal peptide synthetase for bacillomycin L biosynthesis, bmyL operon (bmyLDABC), using genome analysis of TCG15. The bmyLD gene-disrupted mutant did not produce bacillomycin L, plipastatin, or surfactin A. The mutant showed no antifungal activity, indicating an essential role of cLPs. Among the cLPs, bacillomycin L was identified as the key antifungal compound. This activity was enhanced by surfactin A, which showed no antifungal activity alone. These findings suggested that the synergistic interaction between bacillomycin L and surfactin A contributed to the antifungal activity of TCG15.