Influence of Agaricus Bisporus Establishment and Fungicidal Treatments on Casing Soil Metataxonomy During Mushroom Cultivation

Abstract

The cultivation of edible mushroom is an emerging sector with a potential yet to be discovered. Unlike plants, it is a less developed agriculture where many studies are lacking to optimize the cultivation. Mushrooms are a source of resources still to be revealed, which have applications not only in food, but in many other sectors such as health, industry and biotechnology. Mushroom cultivation consists of the development of selective substrates through composting where the mushroom grows via solid fermentation process. In case of Agaricus bisporus, the compost fully colonized by mycelium hardly produces mushrooms and it is necessary to apply a casing layer with certain physical, chemical and biological characteristics to shift from the vegetative mycelium to the reproductive one, where the native microbiota plays crucial roles. Currently, the industry faces a challenge to substitute the actual peat based casing materials due to the limited natural resources and the impact on the peatlands where peat is extracted.In this work we have employed high-throughput techniques by next generation sequencing to screen the microbial structure of casing soil employed in mushroom cultivation while sequencing V3-V4 of the 16S rRNA gene for bacteria and the ITS2 region of rRNA for fungi in an Illumina MiSeq. In addition, the microbiome dynamics and evolution (bacterial and fungal communities) in peat based casing along the process of incubation of Agaricus bisporus have been studied, while comparing the effect of fungicidal treatment (Chlorothalonil and Metrafenone). Statistically significant changes in populations of bacteria and fungi were observed. Microbial composition differed significantly based on incubation day, changing radically from the original communities to a specific microbial composition adapted to enhance the A. bisporus mycelium growth. Chlorothalonil treatment seems to delay casing colonization by A. bisporus. Proteobacteria and Bacteroidota appeared as the most dominant bacterial phyla. We observed a great change in the structure of the bacteria populations between day 0 and the following days. Fungi populations changed more gradually, A. bisporus displacing the rest of the species as the cultivation cycle progresses. A better understanding of the microbial communities in the casing will hopefully allow us to increase the biological efficiency during production as well as possibly help us to have a clearer view of the microbial community-pathogen relationships as they are directly related to disease development.