Compost degradation and growth of Agaricus bisporus

Abstract

Reproductive structures of the button mushroom, Agaricus bisporus, form a high quality food source. Its mushrooms are cultivated on straw based compost that is rich in microbes. A. bisporus primarily degrades lignin during its vegetative growth while plant cell wall carbohydrates are primarily consumed when fruiting bodies are formed. Roughly 44 %, 56 %, and 46 % of lignin, xylan, and cellulose, respectively, remain in the compost relative to the when A. bisporus is introduced in the compost after a full cycle of mushroom production. In addition, part of the xylan accumulates as doubly substituted arabinoxylan. In this research, fungal and bacterial biomass in compost was quantified using chitin and PLFA, and PLFA, respectively. Results suggest that a significant fraction of the A. bisporus biomass is dead after colonizing the compost. Moreover, the diet of A. bisporus may consist primarily of bacterial biomass during its vegetative growth. It was attempted to improve substrate utilization of A. bisporus by introducing and overexpressing α-1,3-L-arabinofuranosidase (AXHd3) from Humicola insolens and mnp1, respectively. Production of active AXHd3 did not measurably affect the carbohydrate composition and degree of arabinosyl substitution of arabinoxylans in compost. Overexpression of mnp1 had a minor effect on lignin composition but did not affect carbohydrate content and accessibility. Notably, the capacity of compost extract to consume the MnP co-factor H2O2 was 4- to 8-fold higher than its producing capacity. This may very well explain why over-expression of mnp1 did not improve carbohydrate degradation in compost and makes the H2O2 producing capacity of A. bisporus a target for improving its substrate degradation. Next to substrated degradation mushroom development may be a target for improving A. bisporus cultivation efficiency. Over-expression of the transcription factor c2h2 resulted the yield-per-day peaking one day earlier suggesting that this transcription factor is a target for breeding commercial mushroom strains. Finally, synchronized respiratory bursts that are associated with the vegetative growth of A. bisporus were observed in compost. These bursts are associated with changes in CO2 production, O2 consumption, compost temperature, and an increased respiratory quotient. The bursts occur synchronous throughout the compost and evidence points to the requirement of mycelium interaction for their synchronization.