Organohalide respiration in a pristine hypersaline lake

Despite compiling evidence on distribution of organohalide-respiring bacteria (OHRB) in pristine environments, there is lack of knowledge about their occurrence and potential contribution to the chlorine cycle in extreme environments such as hypersaline lakes. Biotic formation of organohalides (OHs) such as chloromethane and chloroform was recently reported from the hypersaline Lake Strawbridge, Australia. Assuming that natural availability of OHs can prime development of organohalide respiration potential, we prepared microcosms from Lake Strawbridge sediments. Amended chloroform and tetrachloroethene (PCE) were stoichiometrically dechlorinated to dichloromethane and trichloroethene, respectively. MiSeq 16S ribosomal RNA gene analysis and quantitative PCR did not detect any known chloroform and PCE-dechlorinating OHRB in anaerobic sediment microcosms and transfers, which indicated the presence of novel OHRB in hypersaline Lake Strawbridge. To our knowledge, this is the first report on OHR occurrence in extreme pristine environments. Combined with the formerly documented biotic chlorination, this suggests interdependencies between microbial chlorinators and dechlorinators in the local chlorine cycle in an extreme ecosystem.