Unusual bacterial populations observed in a full-scale municipal sludge digester affected by intermittent seawater inputs.

This study investigated the bacterial community of a full-scale anaerobic digester, which suffers from intermittent seawater contaminations, using 16S rRNA gene clone analysis over different seasons. Bacteroidetes, Proteobacteria, and unclassifiable bacteria were the three major bacterial groups within the clone library (a total of 290 clones). A significant portion of the total clones (29.3%) was not affiliated to any previously reported phylum, and 55.3% of the unclassifiable clones (16.9% of the total clones) showed potential relations to the species of Thermotogae, rarely present under normal mesophilic anaerobic conditions. These results suggested that the novel populations may have the potential to play an important role in anaerobic processes, particularly under abnormal environmental conditions. Additionally, statistical analysis supported that seasonal variations in influent characteristics, and potential competitions among different populations, may be related to the unusual bacterial diversity and community dynamics observed over the study period.