Volume 19 Part 1 Article 33
Title: New insights into the microbial communities and biological activities that define mushroom compost
Author: Michael Kertesz, Katarzyna Safianowicz and Tina Bell
The yield and quality of a mushroom crop is vitally dependent on maintaining consistent, reliable quality in the mushroom compost used as a growth substrate. Achieving this consistency requires an in-depth understanding of the biology of the composting process. Detailed chemical and biological data were obtained for a standard composting run and mushroom production run under conditions typical for the Australian mushroom industry. Activities of eleven different compost enzymes were determined, along with physicochemical measurements and analysis of the microbial community (T-RFLP and Illumina sequencing) at 37 timepoints from raw materials through composting to the end of the mushroom production process, examining both casing and compost during three flushes of mushroom cropping. Enzymatic activities in compost were highest during the pre-wet phase, and decreased by the end of rick turn, sharply increased during Phase 2 (after pasteurization), only to decrease again throughout spawn run. Near infrared fingerprints, a technique used for characterizing organic samples, revealed clear differences between casing and compost at various stages of composting and mushroom production, suggesting this may be a useful methodology in characterizing compost and casing in future research. Over 30,000 different microbes were identified in compost with highest diversity at the end of Phase 1 and an obvious biological succession throughout the whole process. The bacterial community in Phase 1 was dominated successively by an Acinetobacter followed by Bacillus, an unidentified Proteobacterium and Thermus. In Phase 2 and Phase 3, the main bacteria were a Pseudoxanthomonas strain together with Steroidobacter and Chitinophaga. The fungal community also showed a strong biological succession during pre-wet and Phase 1, with a strain of Lewia dominating initially, followed by Myceliophora, an unidentified fungus, a strain of Penicillium, and Scytalidium thermophilum. Scytalidium thermophilum dominated throughout Phase 2 and Phase 3 until it was overgrown by Agaricus during the spawn run. The data obtained represent the most detailed biochemical and molecular study yet undertaken of the mushroom composting process, and have revealed the complexity of microbial populations present in high yielding compost, many of which have never been identified before. More work is required to confirm which of these are essential for composting, and which could potentially be used as supplements to promote composting efficiency.