Distribution and abundance of Spirochaetes in full-scale anaerobic digesters.

To investigate the distribution and abundance of spirochaetal communities within anaerobic digesters, pyrosequencing of the 16S rRNA gene was conducted. Phylogenetic analysis identified a cluster which included the majority of core spirochaetal operational taxonomic units (OTUs) and environmental clones but no pure-culture strains. Distribution of the core OTUs demonstrated an importance of local factors in shaping the structure of Spirochaetes. Spirochaetal to bacterial 16S rRNA gene copy numbers varied from 1.3% to 30.0% depending on digester samples. Environmental variables were found to influence the relative abundance of Spirochaetes. In a batch anaerobic digestion experiment testing the response to different substrates, acetate most stimulated the activity of Spirochaetes, suggesting possible acetate oxidation by syntrophic acetate oxidation process. Taken together, the results obtained in this study provides an insight into the ecology of Spirochaetes in anaerobic digesters and a basis for future studies examining ecological function of these bacteria.