Microbial diversity in a bagasse-based compost prepared for the production of Agaricus brasiliensis

Edible mushrooms are renowned for their nutritional and medicinal properties and are thus of considerable commercial importance. Mushroom production depends on the chemical composition of the basic substrates and additional supplements employed in the compost as well as on the method of composting. In order to minimise the cost of mushroom production, considerable interest has been shown in the use of agro-industrial residues in the preparation of alternative compost mixtures. However, the interaction of the natural microbiota present in agricultural residues during the composting process greatly influences the subsequent colonisation by the mushroom. The aim of the present study was to isolate and identify the microbiota present in a sugar cane bagasse and coast-cross straw compost prepared for the production of Agaricus brasilienses. Composting lasted for 14 days, during which time the substrates and additives were mixed every 2 days, and this was followed by a two-step steam pasteurisation (55 - 65°C; 15 h each step). Bacteria, (mainly Bacillus and Paenibacillus spp. and members of the Enterobacteriaceae) were the predominant micro-organisms present throughout the composting process with an average population density of 3 x 10(8) CFU/g. Actinomycetes, and especially members of the genus Streptomyces, were well represented with a population density of 2 - 3 x 10(8) CFU/g. The filamentous fungi, however, exhibited much lower population densities and were less diverse than the other micro-organisms, although Aspergillus fumigatus was present during the whole composting process and after pasteurisation.