Characterization of a Dehalobacter Coculture That Dechlorinates 1,2-Dichloroethane to Ethene and Identification of the Putative Reductive Dehalogenase Gene

Abstract

Dehalobacter and "Dehalococcoides" spp. were previously shown to be involved in the biotransformation of 1,1,2-trichloroethane (1,1,2-TCA) and 1,2-dichloroethane (1,2-DCA) to ethene in a mixed anaerobic enrichment culture. Here we report the further enrichment and characterization of a Dehalobacter sp. from this mixed culture in coculture with an Acetobacterium sp. Through a series of serial transfers and dilutions with acetate, H 2 , and 1,2-DCA, a stable coculture of Acetobacterium and Dehalobacter spp. was obtained, where Dehalobacter grew during dechlorination. The isolated Acetobacterium strain did not dechlorinate 1,2-DCA. Quantitative PCR with specific primers showed that Dehalobacter cells did not grow in the absence of a chlorinated electron acceptor and that the growth yield with 1,2-DCA was 6.9 (؎0.7) ؋ 10 7 16S rRNA gene copies/mol 1,2-DCA degraded. PCR with degenerate primers targeting reductive dehalogenase genes detected three distinct Dehalobacter/Desulfitobacterium-type sequences in the mixed-parent culture, but only one of these was present in the 1,2-DCA-H 2 coculture. Reverse transcriptase PCR revealed the transcription of this dehalogenase gene specifically during the dechlorination of 1,2-DCA. The 1,2-DCA-H 2 coculture could dechlorinate 1,2-DCA but not 1,1,2-TCA, nor could it dechlorinate chlorinated ethenes. As a collective, the genus Dehalobacter has been show to dechlorinate many diverse compounds, but individual species seem to each have a narrow substrate range.

Isolation of Acetobacterium sp. Strain AG, Which Reductively Debrominates Octa- and Pentabrominated Diphenyl Ether Technical Mixtures

“…S4D and E in the supplemental material). It is speculated that Acetobacterium may provide certain growth factors for Dehalococcoides for synthesis of necessary dehalogenases that are responsible for PBDE debromination, as implied by previous coculture studies with Acetobacterium/Dehalobacter (35), Sedimentibacter/Dehalobacter (36), and Enterococcus/Desulfitobacterium (37) (nondechlorinating supporter/dechlorinator). Acetobacterium spp.…”

Overview of organohalide-respiring bacteria and a proposal for a classification system for reductive dehalogenases

“…The preponderance of these organisms is partially due to the intense research efforts concentrated on these bacterial groups based on their environmental significance as dechlorinating organisms, but is also due to the fact that genomes from these organisms typically contain multiple rdhA genes [20,32,80,94].…”

“…These RDases are distributed across the RdhA tree, and are known to catalyse the dehalogenation of a broad range of substrates, including chlorinated ethenes (VcrA, BvcA, TceA, MbrA, PceA, PrdA [38,40,54,60,74,93,100]), chlorinated ethanes (CfrA, DcrA, DcaA [73,81,94]), and chlorinated aromatics (CbrA, CprA [31,71,75,101]). For most characterized reductive dehalogenases, the full substrate range is not known; instead activity on a specific substrate has been verified.…”

The restricted metabolism of the obligate organohalide respiring bacterium Dehalobacter restrictus: lessons from tiered functional genomics

“…[11][12][13][14], suggesting that the degradation potential of the genus Dehalobacter is largely beyond PCE and TCE. Finally, fermentation of dichloromethane by members of Dehalobacter has been shown [15,16], suggesting that not necessarily all members of this genus are obligate OHR bacteria (OHRB).…”