Taxonomic and Metabolic Microbial Diversity During Composting

A great variety and high numbers of aerobic thermophilic heterotrophic and/or autotrophic bacteria growing at temperatures between 60–80°C have been isolated from thermogenic (temperature 60–80°C) composts in several composting facilities in Switzerland. They include strains related to the genus Thermus (T. thermophilus. T. aquaticlls. and several other new strains). Bacillus schlegelii, Hydrogenohacter spp., and of course heterotrophic sporeforming Bacilli. This contrasts with the generally held belief that thermogenic composts (> 60°C) support only a very low diversity of heterotrophic thermophiles. This biodiversity suggests efficient decomposition of organic matter at temperatures above 60°C, and a good thermo-hygienization.During the terminal cooling or maturation phase of composts high numbers and a great metabolic diversity of mesophilic bacteria was observed, including nitrogen-fixers. sulfur-oxidizers. hydrogen-oxidizers, nitrifyiers. and producers of extracellular polysaccharides or bacterial humin. This microbial diversity plays an essential role for compost stabilization. It is suggested that mature compost application improves soil chemistry and microbiology, and can thus be regarded beneficial for agriculture.