Genome analysis and reductive dehalogenase expression of two organohalide-respiring Halodesulfovibrio strains isolated from estuarine sediments

AIMS: Organohalide-respiring bacteria, which utilize organohalides as electron acceptors for energy conservation, play an important role in the global halogen cycle. Organobromine compounds, both natural and anthropogenic, are prevalent in marine habitats, and we therefore aimed to characterize debrominating bacteria from estuarine and marine habitats. METHODS AND RESULTS: We isolated two anaerobic debrominating bacteria, strain AK and strain HS, of the family Desulfovibrionaceae (in the phylum Thermodesulfobacteriota) from estuarine sediments in New Jersey, USA. Their growth was supported by lactate as a carbon source and 2,6-dibromophenol or sulfate as an electron acceptor, but not lactate alone, indicating that respiratory reductive dehalogenation or sulfate reduction is used for energy generation. In addition to 2,6-dibromophenol, these two strains can also dehalogenate a variety of other brominated compounds. Debrominating activity was not influenced by the presence of sulfate or exogenous cobalamin. Whole genome comparison indicates that these two strains share high similarity with an average nucleotide identity (ANI) of 97.8% and share low similarity (ANI < 90%) with other Halodesulfovibrio species (Halodesulfovibrio marinisediminis, Halodesulfovibrio aestuarii, and Halodesulfovibrio spirochaetisodalis). Whole genome-based phylogenetic analysis indicates that these two strains belong to the genus Halodesulfovibrio and likely represent a new species. Their genomes encode three putative reductive dehalogenase genes and the genes encoding for corrinoid biosynthesis and salvaging. Transcriptional analysis of reductive dehalogenase genes shows that the expression of one reductive dehalogenase gene (rdhA1) is induced by 2,6-dibromophenol, indicating its function in debromination. CONCLUSIONS: This study expands our knowledge about the organohalide respiring potential of marine and estuarine Thermodesulfobacteriota.