Microbial dynamics in Australian mushroom compost

Abstract

Button mushrooms (Agaricus bisporus) are highly nutritious, containing key minerals, vitamins and high levels of protein (~25% of dry weight). They are grown on a composted substrate made from wheat straw, poultry manure and gypsum. The composting process is a microbially driven and highly aerobic process. It is a high heat composting process with a final curing stage. A previous study using a single compost yard showed that during the pasteurisation/curing phase, there is a stable bacterial co-existence of Pseudoxanthomonas, Steroidobacter and a novel chitin degrading bacterium from the Chitinophagaceae family, and the dominant fungus is Mycothermus thermophilus. In this study, DNA sequencing revealed compost microbes during the curing stage were dominated by the ascomycete Mycothermus thermophilus, and the bacterium Pseudoxanthomonas, in all compost yards studied. Pseudoxanthomonas has been known to produce nitrous oxide (N2O) in aerobic and microaerobic environments. However, under these conditions the N2O released was very low, suggesting that other compost microbes may be using the N2O as an energy source. In vitro interactions of M. thermophilus, Pseudoxanthomonas spp. and a novel chitin degrading bacterium (Family Chitinophagaceae) showed that M. thermophilus boosted the growth of all bacteria. Understanding the interactions between compost microbes will aid in determining where losses in nitrogen occur and how to optimise nutrient inputs and maximise outputs.