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.IMPORTANCE"Sanghuang" mushroom is a valuable edible and medicinal fungus. It provides numerous health benefits, including antitumor, anti-inflammatory, and immunity-enhancing properties. However, its growth is affected by green mold disease caused by Trichoderma, which severely hampers yield and quality. Conventional fungicide-based control methods have drawbacks like health and environmental risks, as well as the emergence of resistant pathogens. This study innovatively focuses on Bacillus velezensis HX0039, a strain proven to be safe for both "Sanghuang" mushrooms and mice. In vivo and in vitro experiments showed that HX0039 not only exhibits strong antifungal activity but also effectively prevents and controls the occurrence of "Sanghuang" green mold disease. Furthermore, the novelty of this research lies in its potential mechanism of action: HX0039 produces diverse metabolites like lipopeptides (especially iturin A), macrolactin A, and bacillibactin to exert its antagonistic activities. Therefore, this work demonstrates the great potential of B. velezensis HX0039 as an alternative to chemical fungicides in "Sanghuang" production.