Organohalide respiration by a Desulforhopalus-dominated community

Despite the fact that several potential organohalide-respiring bacteria (OHRB) were discovered in metagenome-assembled genomes (MAGs) in our previous study of marine sediments from Aarhus Bay, delineation of their roles and interactions are yet to be disentangled. Henceforth, obtaining corresponding pure cultures or more defined consortia would be highly instrumental for more detailed eco-physiological studies. To this end, we isolated a colony from an anaerobic slant tube culture inoculated with a stable PCE dehalogenating enrichment. Intriguingly, the derived culture exhibited debromination only, instead of PCE dechlorination, under sulfate-reducing conditions. The culture was capable of conserving energy for growth via debromination of 2,6-dibromophenol (2,6-DBP). Analysis of 16S rRNA gene sequence data extracted from shot gun metagenome sequences revealed that a strain belonging to Desulforhopalus was the predominant member of the consortium at a relative abundance of 29 %. Moreover, five bins (completeness > 85% and contamination < 3%) were assembled and all were identified as potentially new species (average nucleotide identity, ANI < 95%). Two bins from potential OHRB, bin.3 belonging to Desulfoplanes, and bin.4 belonging to Marinifilaceae, were found to encode reductive dehalogenase (RDase) genes, whereas bin.5 was found to contain a gene coding for thiolytic tetrachloro-p-hydroquinone (TPh-) RDase bearing 23.4 % identity to TPh-RDase of Sphingobium chlorophenolicum. The expression of all three RDase genes was strongly-induced after adding 2,6-DBP. Acetylene, a known inhibitor of different redox-active metalloenzymes, was found to inhibit methanogenesis as well as reductive dehalogenation without affecting gene expression, suggesting post-transcriptional inhibition. Phylogenomic analyses revealed the ecological importance of complementary roles of community members, including complete de novo vitamin B12 biosynthesis, which agreed with physiological data. Altogether, the findings presented here provided insight into the mutualism of the consortium and provided leads for synthetic OHR community optimization strategies for in situ bioremediation.