Long-term monitoring of the succession of a microbial community in activated sludge from a circulation flush toilet as a closed system.

The microbial diversity and community succession of a circulation flush toilet were investigated by terminal restriction fragment length polymorphism and cloning analyses. Clonal libraries of 16S rRNA gene on day 3 and day 127 were constructed. On day 3, 102 clones were sequenced; Proteobacteria and Bacteroidetes accounted for 27% and 45%, respectively. On day 127, Proteobacteria had increased to 43% and Bacteroidetes had decreased to 26% of a total of 100 clones. Terminal restriction fragment length polymorphism peaks were identified by in silico analysis of clone libraries. The relative abundances of Nitrosomonas increased from 1% to 6% with commencement of nitrification and denitrification. Similarly, the relative abundance of terminal restriction fragments generated from Xanthomonas increased from 3% to 10%. Therefore, these bacteria could play a prominent role in this process. To reveal the relationship between stability of the microbial community and performance of the system, microbial community succession was visualized by multidimensional scaling analysis. The microbial community structure changed markedly, particularly during the start-up period of the system. The plots then became stable after the start of nitrification and denitrification. This result suggests that the succession of microbial community structure had a correlation with the performance of the system.