Researchers isolated and characterized seven strains of extremely halophilic, sulfur-oxidizing bacteria from hypersaline lakes in Siberia and a Mediterranean solar saltern. These obligately chemolithoautotrophic bacteria, which require high salt concentrations (optimum 3.0 M NaCl) and neutral pH (6.5–8.2), represent a novel genus and species designated Thiohalorhabdus denitrificans. The bacteria oxidize thiosulfate and tetrathionate as electron donors, producing tetrathionate as an intermediate during aerobic growth and elemental sulfur during anaerobic growth. Uniquely among chemolithoautotrophs, they can grow anaerobically using nitrate as an electron acceptor while oxidizing inorganic sulfur compounds. Cells accumulated glycine betaine as their primary compatible solute and possessed distinctive fatty acid profiles dominated by 10MeC16:0 and C16:0. Phylogenetic analysis revealed these organisms represent an independent, deep-branching lineage within Gammaproteobacteria with no close relationship to other known genera. DNA–DNA hybridization confirmed all seven isolates constituted a single genomic species despite originating from geographically distant locations.

Key findings

• Thiohalorhabdus denitrificans is a novel genus of extremely halophilic, obligately chemolithoautotrophic sulfur-oxidizing bacteria capable of both aerobic and anaerobic (denitrifying) growth
• The bacteria require extreme salt concentrations (2.0–5.0 M NaCl, optimum 3.0 M) and absolute dependence on both Na+ and Cl− ions for survival
• They form tetrathionate as a characteristic intermediate during thiosulfate oxidation and accumulate high concentrations of glycine betaine as a compatible solute
• Phylogenetic analysis places them as an independent deep lineage within Gammaproteobacteria with <88% sequence similarity to other culturable members of the class
• Seven isolates from geographically distinct hypersaline habitats showed 70–85% DNA–DNA relatedness, confirming they represent a single genomic species