An Exploration into the Bacterial Community under Different Pasteurization Conditions during Substrate Preparation (Composting–Phase II) for Agaricus bisporus Cultivation

Abstract

Substrate preparation (i.e., composting) for Agaricus bisporus cultivation is the most critical point of mushroom production. Among many factors involved in the composting process, the microbial ecology of the system is the underlying drive of composting and can be influenced by composting management techniques. Pasteurization temperature at the beginning of phase II, in theory, may influence the bacterial community and subsequently the "selectivity" and nutrition of the final substrate. Therefore, this hypothesis was tested by simulation in bioreactors under different pasteurization conditions (57 °C/6 h, 60 °C/2 h, and 68 °C/2 h), simulating conditions adopted by many producers. Bacterial diversity, based on 16S ribosomal RNA obtained by high-throughput sequencing and classified in operational taxonomic units (OTUs), was greater than previously reported using culture-dependent methods. Alpha diversity estimators show a lower diversity of OTUs under a high-temperature pasteurization condition. Bacillales order shows a relatively higher OTU abundance under a high-pasteurization temperature, which also was related to high ammonia emission measurements. On the other hand, beta diversity analysis showed no significantly changes in the bacterial community structure under different conditions. Agaricus bisporus mycelium growth during a standard spawn run period was significantly slower in the compost pasteurized at high temperature. Since the bacterial community structure was not greatly affected by different pasteurization conditions but by-products left (e.g., ammonia) at the end of compost conditioning varied, further studies need to be conducted to determine the functional role of the microbial communities found during substrate preparation for Agaricus bisporus cultivation.

Growing edible mushrooms: a conversation between bacteria and fungi

“…The relative abundance of the order Bacillales has been reported to increase in conjunction with high ammonia emission during the pasteurization stage of phase II, with the native microbiota providing an intensive cellulose‐degrading consortium (Fig. B; Szekely et al ., ; Vieira and Pecchia, ).…”

“…The microbiota (mainly from the manure fraction) grows, releasing ammonia and softening the mixture. Firmicutes , Proteobacteria , Actinobacteria , Bacteroidetes and Thermi are the dominant phyla during phase I (Zhang et al ., ; Vieira and Pecchia, ), while among the fungal microbiota, Ascomycota appears to be the most abundant phyla during phase I (Kertesz et al ., ; our unpublished results).…”

“…; Kertesz et al . ; Kertesz and Cai, ; Vieira and Pecchia, ). Ammonia generated during pasteurization can adversely affect A. bisporus mycelium growth while favouring fungal competitors and parasites such as Trichoderma spp.…”

Exploring oyster mushroom (Pleurotus ostreatus) substrate preparation by varying phase I composting time: changes in bacterial communities and physicochemical composition of biomass impacting mushroom yields

“…Ten (200 g each) random subsamples were taken across the substrate ricks, which were mixed/homogenized manually and immediately frozen at −20°C until DNA extraction. The DNA extraction was done following the procedures described by Vieira and Pecchia (). Subsequently, extracted genomic DNA was visualized in an agarose gel (1%, 100v for 45 min) and quantified using a spectrophotometer (NanoDrop 2000/2000c model; Thermo Scientific, Madison, WI).…”

“…Conditioning temperature ranges are typically between 45 and 50°C for 3–10 days and conditioning is necessary to remove the ammonia formed during phase I, to break down carbohydrate sources (hemicellulose and cellulose) and to establish a beneficial microbiota, which can feed and/or stimulate mushroom growth (Gerrits ; Straatsma et al . ; Vieira and Pecchia ).…”