Anaerobic reductive dechlorination of chlorobenzenes by an enrichment culture containing Dehalobacter species

Abstract

Chlorinated benzenes are pervasive contaminants in soil and groundwater at industrial sites globally. We previously obtained an anaerobic 1,2,4-trichlorobenzene-dechlorinating enrichment culture originated from a chemical plant. In this study, we evaluated the dehalogenation capability of this consortium to utilize all chlorobenzene congeners as the ultimate electron acceptors. Over a period of approximately 250 days’ incubation, 11 out of 12 chlorobenzene congeners were successfully dechlorinated to monochlorobenzene, suggesting that the consortium has no preferential dehalogenation pattern for flanked chlorines on the benzene ring. Distinct dechlorination pathways strongly suggested that novel dechlorinator and reductive dehalogenases prevailed in this consortium. The 16S rRNA gene amplicon sequencing revealed that the microbial communities were predominantly composed of fermenters such as Sporomusa, Desulfitobacterium and Longilinea; methanogenic Methanobacterium; and the organohalide-respiring bacterium Dehalobacter. The bottles actively engaged in chlorobenzene dechlorination harbored higher abundances of Dehalobacter species. Quantitative PCR analysis further demonstrated that Dehalobacter conserved energy from chlorobenzene dechlorination, with growth yields ranging from 1.2 × 10⁵ to 2.27 × 10⁷ copies per μmol of Cl⁻ released. The versatile chlorobenzene dechlorination capacities of the consortium underscores its significant potential for remediating chlorobenzene-contaminated field sites.