The dominance of Bacteroidetes, Firmicutes and Chloroflexi was also found in other OSS_128167 previous studies. In addition, R3 with 20% feeding TS content had high relative abundance of Spirochaetes, Tenericutes and Proteobacteria. Although most bacteria in reactors were affiliated to these dominant phyla, the relative abundances of these phyla in each reactor were different and each digester had its own characteristic bacterial community composition. The proportion of phylum Chloroflexi in each reactor was the highest in this study. This was in good accordance with previous reports that Choroflexi populations were abundant in anaerobic digesters, as determined by membrane hybridization, FISH and 16S rRNA gene clone analysis. Rivie`re et al., also found large proportions of Chloroflexi sequences in municipal WWTP sludge samples. An important trend is the small proportion of Choroflexi at the highest TS content: 31% for the 20% TS, compared to 58% with the 15% TS and 65% at the 5% TS. The proliferation of Choroflexi, a well known scavenger biomass-derived organic carbon such as soluble microbial products, supports a greater influence of difficult-to-biodegrade organic materials from the input substrates and from endogenous dacay of the anaerobic biomass. For R1-R3 at a fixed SRT, increased feeding TS of FW meant higher applied OLR and larger amount of easily degradable substrate per unit volume for microorganisms, which resulted in a smaller relative abundance of phylum Choroflexi. On the other hand, the Bacteroidetes population was enriched in the reactors with higher TS contents. The phylum Bacteroidetes are proteolytic bacteria and were probably involved in the degradation of various proteins used for anaerobic Ceftizoxime digestion studies. The majority of proteolytic microorganisms are able to metabolize amino acids to produce VFA such as acetate, propionate and succinate and NH3. Interestingly, their selective enrichment at high TS contents seems to be in consistent with the observation of high protein-input rate and VFA production in the reactors with higher TS contents. This result indicated the importance of the Bacteroidetes performing protein hydrolysis. However, the changing trend of relative abundance of the phylum Firmicutes was not obvious with increasing TS contents.