Hot air pasteurisation may facilitate symbiosis between fungus Lentinula edodes and bacteria

This study was to experimentally investigate 1) microbial community composition in the shiitake growing substrates subjected to either autoclaving or hot-air pasteurisation; and 2) the roles of isolated bacteria on shiitake mycelial growth. Different heat-treated birch-based substrates with and without shiitake inoculum were incubated in a respirator and used for the microbial community study. Microbial community in the substrates after the colonization were profiled by phosphate-lipid fatty acid (PLFA) analysis and DNA sequencing. Furthermore 10 bacterial strains were isolated and identified from fully-colonised substrate subjected to 75 °C hot-air pasteurisation, and individual effects of each strain on mycelial growth of shiitake were investigated. Shiitake colonised well on all substrates, regardless pasteurizing temperatures and coexisting microbes; there was no significant difference in total microbial respiration and PLFA biomass between pasteurization regimes. DNA sequencing of the prokaryotic in the substrates showed that genera Phyllobacterium, Sphingomonas, and Pelomonas within phylum Proteobacteria dominated in all inoculated substrates. Interestingly, two out of ten isolated strains that showed growth promoting effects on the shiitake mycelium were instead affiliated to phylum Firmicutes. It is evident that the microbial ecology of growth promoting bacteria on shiitake mycelium is complex and further investigation is required to elucidate the mechanism.