Introduction

A precious basidiomycete fungus, Inonotus baumii (formerly Phellinus baumii), has been widely utilized in China, Japan and other Asian countries as a traditional Chinese medicinal mushroom [1, 2]. In China, I. baumii is commonly called ‘Sanghuang’ mushroom, a yellow fungus that grows on mulberry. It is regarded as being advantageous to human health due to its high biological activities, including antitumor, anti-inflammation, and antioxidation effects [3,4,5]. Numerous studies have documented that natural compounds such as polysaccharides, flavones, and ergosterol are the bioactive metabolites responsible for the medicinal and gastronomic value of ‘Sanghuang’ [6, 7]. In recent years, indoor artificial cultivation of ‘Sanghuang’ mushroom has been developed and practiced on a large scale in China [58,59]. For hosts, microbial communities are an important line of defense against pathogenic microorganism invasion from the environment [60, 61]. Numerous studies have demonstrated that the health status of a host (e.g., plant or mushroom) is a result of complex interactions between the host, the soil environment, and microorganisms, including pathogens and other microorganisms in the soil or within the plant, indicating that the richer and more diverse the microbial community in the habitats of the host is, the more complex the interspecific interactions, and the stronger the ability of the host to resist invasion by external pathogenic microorganisms [62,63,64]. Our findings indicated that HC samples had more OTUs, higher α-diversity, and greater microbial community complexity than FC samples. Analogous to findings for other hosts [13, 65], we speculated that there were connections between the microbial community structure and growth status of ‘Sanghuang’ mushroom.

With the emergence of limitations in traditional control methods for host diseases (e.g., chemical control and resistance breeding), the current methods of biological control for host diseases involving a search for natural antagonistic microorganisms have attracted widespread attention [43]. In recent years, the application of Bacillus and Pseudomonas as biocontrol strains has been studied in depth [66, 67]. Chen et al. [68] reported that Bacillus subtilis 151B1 and YBC could be used as potential biological agents to control passion fruit disease caused by Fusarium solani. Ren et al. [69] revealed that Pseudomonas poae JSU-Y1 had the potential to control the growth of toxigenic fungi in agricultural products. Our collection of bacteria antagonistic to Trichoderma also included members of Bacillus and Pseudomonas. Furthermore, we also performed a screening experiment of antagonistic bacteria against Fusarium, and the study showed that the antagonistic bacteria also included Bacillus with a good antifungal effect (data not shown). Notably, Bacillus spp. (HX0037, HX0016, and HX0039) exhibited outstanding inhibitory activity against Trichoderma FZ0005, suggesting that they might serve as potential biological resources for the biocontrol of ‘Sanghuang’ diseases. As reported in other studies, the use of biofungicides based on Bacillus species could be regarded as a biological alternative to synthetic fungicides employed in mushroom production [20, 70]. We suggest that a bacterial suspension of Bacillus strains with antifungal activity against Trichoderma FZ0005 should be sprayed onto the cultivation soil or the surface of bag-cultivated ‘Sanghuang’ mushrooms during propagation and at the stage of fruiting body formation. Moreover, adding beneficial Bacillus (HX0037, HX0016, and HX0039) bacteria to water tanks used for daily irrigation might provide an additional strategy for disease management. The biocontrol activity and mechanism of these antagonistic bacteria, however, remain to be further characterized. According to our findings, we hypothesized that Bacillus occupied a dominant ecological niche in the soil microbiome of HC, which not only stabilized the soil microecosystem but also effectively antagonized the major pathogen causing the fungal diseases of ‘Sanghuang’, thereby possibly reducing the production of mold conidia released into the air.

Conclusions

High-throughput sequencing technology and traditional culture-dependent methods were used to analyze the structure of soil microbial communities of ‘Sanghuang’ mushroom suffering from fungal diseases. Our results revealed that cultivation mode could influence the structure of soil microbial communities of ‘Sanghuang’ mushroom, and the Trichoderma genus was the major causal agent of ‘Sanghuang’ fungal diseases. Three Bacillus spp. (HX0037, HX0016, and HX0039) exhibited effective antifungal activity against Trichoderma sp. FZ0005 and might be useful as future biocontrol agents against fungal diseases affecting ‘Sanghuang’ mushroom.