Community dynamics of methanotrophic bacteria during composting of organic matter

In this study, we describe the effects of composting on the diversity, abundance and activity of the methanotrophic community present in the compost. Composting was allowed to proceed for 10 weeks in an in-vessel reactor. Self-heating capacity (Rottegrad) indicated that compost maturity was reached after 4 weeks. After 6 weeks, a second thermophilic phase was induced by manually increasing temperature to investigate whether or not the methanotrophs shifted back to the thermophilic population. Polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE) with primers specific for type I methanotrophs of 16S rDNA and 16S rRNA were used to characterize the composition of the microbial community. Cluster and diversity analyses of RNA DGGE patterns were more sensitive than those of DNA DGGE patterns, and revealed that mesophilic and thermophilic methanotrophic communities could be differentiated. Moreover, it was seen that the diversity of the community was low during the thermophilic phase and increased during the final maturation phase. Real-time PCR analysis was also performed on the DNA and RNA extracts and showed no changes in the abundance of type I methanotrophs during the composting process (109 DNA copies/g compost). However, RNA-related activity did change, with the lowest activity (107 cDNA copies/g compost) observed during the thermophilic phase, subsequently increasing to its maximum value (109 cDNA copies/g compost), and finally decreasing during the maturation phase. This study confirmed the population dynamics, as seen for general groups such as bacteria and fungi during composting, for a very specific and sensitive group of bacteria, it is the type I methanotrophs.