Bacillus subtilis is crucial for the normal growth of mycelium for Stropharia rugosoannulata.

Stropharia rugosoannulata is an important commercially cultivated edible mushroom worldwide. It grows slowly, and even does not grow at all on completely sterilized substrates, which has limited the spawn manufacture. In this article, it was found that the mycelium growth rate of S. rugosoannulata on non-sterilized or incompletely sterilized sawdust medium is 90%-125% faster than that on completely sterilized sawdust medium. The strain T2-19 with promoting effect on the mycelium growth was isolated from the substrate colonized by S. rugosoannulata. The phylogenetic analysis based on 16S rRNA gene, the average nucleotide identity (ANI), the average amino acid identity (AAI), and the digital DNA-DNA hybridization (dDDH) analysis at the genomic level indicate that strain T2-19 belongs to Bacillus subtilis. On the completely sterilized sawdust medium, inoculation of B. subtilis can increase significantly the growth rate of mycelium by 8.63% - 46.82% depending on the bacterial quantity inoculated. B. subtilis disperse over long disperses in sawdust media by utilizing the mycelium of S. rugosoannulata as fungal highway without causing any symptoms of microbial contamination. It is speculated that B. subtilis is the key microorganism to promote the mycelium growth of S. rugosoannulata in the non-sterilized sawdust medium. Inoculation with B. subtilis can alter the specific activity of lignocellulosic enzymes including cellulase, laccase, and Mn-peroxidase, but it still cannot explain the mechanism by which B. subtilis promotes the mycelium growth of S. rugosoannulata. The results of this article provide new ideas and methods for the production of S. rugosoannulata.