ABSTRACTOrganohalide compounds are widespread in the environment as a result of both anthropogenic activities and natural production. The marine environment, in particular, is a major reservoir of organohalides, and reductive dehalogenation is thought to be an important process in the overall cycling of these compounds.Deltaproteobacteriaare important members of the marine microbiota with diverse metabolic capacities, and reductive dehalogenation has been observed in someDeltaproteobacteria. In this study, a comprehensive survey ofDeltaproteobacteriagenomes revealed that approximately 10% contain reductive dehalogenase (RDase) genes, which are found within a common gene neighborhood. The dehalogenating potential of select RDase A-containingDeltaproteobacteriaand their gene expression were experimentally verified. ThreeDeltaproteobacteriastrains isolated from marine environments representing diverse species,Halodesulfovibrio marinisediminis,Desulfuromusa kysingii, andDesulfovibrio bizertensis, were shown to reductively dehalogenate bromophenols and utilize them as terminal electron acceptors in organohalide respiration. Their debrominating activity was not inhibited by sulfate or elemental sulfur, and these species are either sulfate- or sulfur-reducing bacteria. The analysis of RDase A gene transcripts indicated significant upregulation induced by 2,6-dibromophenol. This study extends our knowledge of the phylogenetic diversity of organohalide-respiring bacteria and their functional RDase A gene diversity. The identification of reductive dehalogenase genes in diverseDeltaproteobacteriaand confirmation of their organohalide-respiring capability suggest thatDeltaproteobacteriaplay an important role in natural organohalide cycling.IMPORTANCEThe marine environment is a major reservoir for both anthropogenic and natural organohalides, and reductive dehalogenation is thought to be an important process in the overall cycling of these compounds. Here we demonstrate that the capacity of organohalide respiration appears to be widely distributed in members of marineDeltaproteobacteria. The identification of reductive dehalogenase genes in diverseDeltaproteobacteriaand the confirmation of their dehalogenating activity through functional assays and transcript analysis in select isolates extend our knowledge of organohalide-respiringDeltaproteobacteriadiversity. The presence of functional reductive dehalogenase genes in diverseDeltaproteobacteriaimplies that they may play an important role in organohalide respiration in the environment.
Genome-Guided Identification of Organohalide-RespiringDeltaproteobacteriafrom the Marine Environment