Biocontrol against fungal mycoparasites driven by Bacillus velezensis strains from a mushroom crop microcosm

The cultivation of button mushroom ( Agaricus bisporus ) requires the design of tailor-made substrates that nourish the crop and promote morphology changes from mycelium to basidiome. The agronomic stages of mushroom development are also influenced by the microbiota present in the mushroom crop microcosm, which may have a beneficial impact on mushroom growth, development and quality, or a detrimental impact through reduction of yield or quality as pathogens, competitors or disease vectors in mushroom crops. Bacillus velezensis strains isolated from commercial mushroom casing material have been demonstrated to have antifungal activity against fungal mycoparasites of mushroom crops. In this report we describe the isolation of multiple strains of B. velezensis from mushroom casing material and basidiomes that show antifungal activity towards major mushroom mycoparasites, along with further characterization of their mode of action. Full genomes of B. velezensis CM5, CM19, CM35, EM5 and EM39 were sequenced and annotated, which together with metabolic profiling of specialised metabolites produced by CM5, CM19 and CM35 suggested that antifungal activity of these strains is linked to the production of the lipopeptide fengycin. However, in crop trials, these strains did not increase mushroom yield or provide significant control of the mushroom pathogen Lecanicillum fungicola. Genomic and analytical tools were designed and used to evaluate B. velezensis persistence in casing when the selected strains were artificially applied. B. velenzensis population levels decreased significantly after application, potentially contributing to the lack of biocontrol activity observed in crop trials.