Detection of a Bacterial Group within the Phylum Chloroflexi and Reductive-Dehalogenase-Homologous Genes in Pentachlorobenzene-Dechlorinating Estuarine Sediment from the Arakawa River, Japan

We enriched a pentachlorobenzene (pentaCB)-dechlorinating microbial consortium from an estuarine-sediment sample obtained from the mouth of the Arakawa River. The sediment was incubated together with a mixture of four electron donors and pentaCB, and after five months of incubation, the microbial community structure was analyzed. Both DGGE and clone library analyses showed that the most expansive phylogenetic group within the consortium was affiliated with the phylum Chloroflexi, which includes Dehalococcoides-like bacteria. PCR using a degenerate primer set targeting conserved regions in reductive-dehalogenase-homologous (rdh) genes from Dehalococcoides species revealed that DNA fragments (approximately 1.5-1.7 kb) of rdh genes were amplified from genomic DNA of the consortium. The deduced amino acid sequences of the rdh genes shared several characteristics of reductive dehalogenases. The mixed culture could be maintained by transferring small inocula into fresh synthetic mineral medium containing either acetate or pyruvate, which supported the dechlorination of pentaCB by acting as an electron donor.