Biocontrol of mushroom crop mycoparasites by novel Bacillus velezensis strains

Abstract

1.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 parasites, competitors or disease vectors in mushroom crops. In this report we describe the isolation of multiple strains of Bacillus 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 the 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 parasite Lecanicillium fungicola. Genomic and analytical tools were designed and used to evaluate B. velezensis persistence in casing when the selected strains were artificially applied. B. velezensis population levels decreased significantly after application, potentially contributing to the lack of biocontrol activity observed in crop trials. 3. Key PointsO_LIB. velezensis strains isolated from peat-based microcosms are shown to have significant inhibitory effects against major fungal parasites of mushrooms in vitro. C_LIO_LIThrough full genome sequencing and metabolic profiling using LC-HRMS, the antifungal activity is correlated with the production of lipopeptides, particularly fengycin analogues. C_LIO_LIIn trials using button mushroom crops artificially infected with Lecanicillium fungicola, the causal agent of dry bubble, treatment of casing material with these strains did not significantly limit dry bubble disease or increase yield. C_LIO_LIThe persistence of strains in crop when artificially applied showed significant decreases after application on casing, potentially contributing to the lack of biocontrol activity. C_LI