Reductive dehalogenation of Desulforhopalus singaporensis. Organohalide respiration of a sulfate-reducer, Desulforhopalus singaporensis

Our previous enrichment studies and multi-omic data analyses indicated that members of the genus Desulforhopalus are capable of reductive dehalogenation (RD). Here, we studied organohalide respiration (OHR) in Desulforhopalus singaporensis, a sulfate reducer, as genome analysis predicted the presence of a respiratory reductive dehalogenase (RDase) gene. Our results revealed that D. singaporensis can debrominate 2,6-dibromophenol (2,6-DBP), 2,4-DBP, and 2,4,6-tribromophenol to phenol and 4-bromophenol, respectively, regardless of the presence of vitamin B12 in the medium, due to its complete de novo biosynthesis of vitamin B12. Debromination of 2,6-DBP suppressed sulfate reduction in D. singaporensis. Interestingly, D. singaporensis was identified as a formatotroph using formate as the electron donor instead of H2 for the Wood-Ljungdahl pathway to conserve energy and fix CO2 leading to the formation of acetate. In addition, D. singaporensis gained more biomass under formatotrophic conditions in the presence of 2,6-DBP compared to the control without additional 2,6-DBP or in the presence of acetylene, previously shown to inhibit reductive debromination, respectively. Furthermore, RDase gene expression profiles showed that the acetylene inhibited RDase activity post-transcriptionally. Altogether, this study experimentally verified the OHR potential of D. singaporensis in the presence of formate, which served as the electron donor and was used in carbon assimilation through the Wood-Ljungdahl pathway.