Abstract
The effects of water availability defined as water activity (aw) or matric water potential (ψm) on microbial community dynamics during the start-up operation of mesophilic fed-batch composting (FBC) of household biowaste were studied using commercially available personal composters. The community changes were monitored for 2 months by direct cell counting, quinone profiling, and 16S rRNA gene sequencing of culturable predominant bacteria. The aw level lowered linearly with operation time and reached around 0.95 at the end of operation. During the steady-state period, aw or ψm had a strong positive correlation with moisture content and ubiquinone content and negative correlation with pH, electric conductivity, and partially saturated menaquinone content. Results of 16S rRNA gene-based phylogenetic identification of the predominant isolates as well as of culture-independent quinone profiling indicated that a drastic population change from ubiquinone-containing members of Proteobacteria to Actinobacteria took place during the overall period of operation. Most of the actinobacterial isolates grew on nutrient agar with an aw of less than 0.98, whereas none of the proteobacterial isolates did. These results suggest that water availability is an important determinant of the population shift from the Proteobacteria to Actinobacteria during the start-up operation of mesophilic fed-batch garbage composting.
