Antagonistic mechanism of Bacillus velezensis HX0039 as a biocontrol agent against Trichoderma virens-induced “Sanghuang” green mold

Abstract

Green mold disease caused by Trichoderma spp. is one of the serious challenges in the production of “Sanghuang” mushroom (Sanghuangporus vaninii). Herein, we report the biocontrol efficacy and related mechanisms of Bacillus velezensis HX0039, an antagonistic strain previously isolated from soil for field cultivation of the “Sanghuang” mushroom. Strain HX0039 exhibited broad-spectrum activity against 17 fungal pathogens, especially Trichoderma virens SH4 (a highly pathogenic strain causing “Sanghuang” green mold), and increased the cell membrane permeability of T. virens in vitro. In the “Sanghuang” mode of green mold disease, HX0039 had no negative effects on the mycelial growth or fruiting body formation of mushrooms and exhibited excellent biocontrol efficacy. Genomic analysis revealed that HX0039 possesses multiple genes that contribute to antimicrobial compound production, and iturin A, fengycin, macrolactin A, surfactin, and bacillibactin were detected through UPLC-Q-Exactive-Orbitrap-MS. Among these metabolites, iturin A may play a role in combating T. virens SH4. Hemolytic tests, cell experiments, and mouse studies demonstrated that HX0039 is a biosafe strain. Our results will provide insights into the antifungal mechanisms of B. velezensis HX0039 and will facilitate the further application of this strain as a biocontrol agent against T. virens-induced “Sanghuang” green mold.