Microbial succession in casing layer shapes bacterial blotch disease associated communities in cultivated white button mushroom: From casing layer to disease
Background: Bacterial blotch is a major disease of cultivated white button mushroom (Agaricus bisporus) traditionally attributed to individual Pseudomonas pathogens. However, the recurrent detection of diverse bacterial taxa in blotch-affected mushrooms suggests that disease may involve broader changes in microbial community organization. We characterized bacterial communities associated with…
Bacterial blotch, a prevalent disease in cultivated white button mushrooms (Agaricus bisporus), was historically linked to specific Pseudomonas pathogens. However, findings indicate that this disease may result from significant shifts in microbial community organization. Researchers analyzed bacterial communities linked to both affected and unaffected mushrooms, studying succession in the casing layer at early, pinning, and harvest stages from two American farms employing 16S rRNA gene sequencing and metagenomics.
Mushroom communities predominantly consisted of Pseudomonas, whether diseased or not, implying the disease was not merely due to increased Pseudomonas abundance. Instead, affected mushrooms showed community restructuring, specific taxon enrichment, and reduced microbial network complexity. Metagenomics data unveiled extensive reorganization within Pseudomonas, with varying shifts among multiple blotch-associated lineages. These changes coincided with shifts in non-Pseudomonas taxa like Mycetocola and Ewingella.
Despite these taxonomic changes, Pseudomonas maintained a consistent functional profile. Disease-associated enrichment was seen in pathways related to central metabolism, O-antigen biosynthesis, and peptidoglycan maturation. Casing communities displayed a clear directional succession, shifting from early dominance by Exiguobacterium and Leuconostoc to later enrichment of Flavobacterium, Pedobacter, and Pseudomonas.
Multiple blotch-associated Pseudomonas lineages were found throughout casing development, with Pseudomonas increasing from roughly 2% in early casing to 51% at harvest at the farm with higher disease incidence. This succession occurred without notable changes in alpha diversity, suggesting that community development primarily involved taxon replacement and redistribution.
These findings support a microbiome-centered approach to understanding bacterial blotch, highlighting disease as a result of host and stage-dependent microbial succession, species-level community restructuring, and altered microbial connectivity. This framework moves beyond the single-pathogen model and emphasizes bacterial blotch as a community-level disease process influenced by the dynamic interactions between the mushroom host and its surrounding microbiome.
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