The microbial community responsible for dechlorination and benzene ring opening during anaerobic degradation of...

This study describes the dechlorination ability of acclimated biomass, the high-throughput sequencing of the 16S ribosomal RNA (rRNA) gene of such microorganisms, and the analysis of their community structure in relation to special functions. Two types of acclimated biomass (AB-1 and AB-2) were obtained via different acclimated treatment processes and were used to degrade 2,4,6‑trichlorophenol. The degradation pathway and characteristics of trichlorophenol degradation were different between the two groups. AB-1 degraded trichlorophenol only to 4-chlorophenol. AB-2 completely dechlorinated trichlorophenol and opened the benzene ring. The 16S rRNA high-throughput sequencing method was employed to examine the microbial diversity. It was found that the microbial richness and diversity of AB-1 were higher than those of AB-2. Firmicutes and Bacteroidetes were 2.7-fold and 4.3-fold more abundant, respectively, in AB-1 than in AB-2. Dechlorination bacteria in AB-1 mainly included Desulfobulbus, Desulfovibrio, Dechloromonas, and Geobacter. The above-mentioned bacteria were less abundant in AB-2, but the abundance of Desulfomicrobium was twofold higher in AB-2 than in AB-1. The two types of acclimated biomass contained different hydrogen (H₂)-producing bacteria. AB-2 showed higher abundance and diversity of hydrogen-producing bacteria. There was no Ignavibacteriae in AB-1, whereas its abundance in AB-2 was 8.4%. In this biomass, Ignavibacteriae was responsible for opening of the benzene ring. This study indicates that the abundance and diversity of microorganisms are not necessarily beneficial to the formation of a functional dechlorinating community. The H₂-producing bacteria (which showed greater abundance and diversity) and Ignavibacterium were assumed to be core functional populations that gave AB-2 stronger dechlorination and phenol-degradation abilities. Control of lower oxidation reduction potential (E_h) and higher temperatures by means of fresh aerobic activated sludge as the starting microbial group, caused rapid complete dechlorination of 2,4,6‑trichlorophenol and benzene ring opening.