Insights into the Versatile Sulfur Metabolism of Sulfurovum sp. MH2-6 Isolated from Deep-Sea Hydrothermal Vent Environments.

In deep-sea hydrothermal ecosystems, inorganic sulfur compounds serve as key energy sources for microbes through oxidation, reduction, or disproportionation reactions. However, to date, the bacteria that disproportionate sulfur remain poorly understood. Here, we characterized the physiological and metabolic characteristics of Sulfurovum sp. MH2-6, which was isolated from hydrothermal sediments of the South Mid-Atlantic Ridge. Based on the results of 16S rRNA gene sequence, average nucleotide identity, and DNA-DNA hybridization value, strain MH2-6 belonged to the same species as Sulfurovum mangrovi ST1-3T. The isolate was able to grow chemolithoautotrophically using thiosulfate, sulfite, or sulfide as the sole energy source, and molecular oxygen as the sole electron acceptor. When using hydrogen as the sole energy source, this bacterium could utilize a wide range of electron acceptors, including oxygen, elemental sulfur, thiosulfate, nitrate, and sulfate. Various organic compounds also supported growth as carbon sources during hydrogen oxidation, suggesting a potential for chemolithomixotrophy. Notably, the isolate could grow via the disproportionation of thiosulfate and elemental sulfur in the presence of ferrihydrite. Further, genome analyses revealed that this bacterium contains a complete reductive citric acid cycle (rTCA) for carbon fixation, multiple hydrogenases, sulfur oxidation, reduction, and transfer enzymes, nitrogenase, and oxygen reductases. Transcriptomic comparisons between sulfur reduction and disproportionation conditions revealed that thiosulfate reductase, type IV sulfide: quinone oxidoreductase, and sulfite dehydrogenase were highly abundant in thiosulfate-disproportionating cultures, while rhodanese-like sulfurtransferases and sulfide dehydrogenase showed increased abundances when grown via elemental sulfur disproportionation. Together, these flexible energy- and carbon-utilizing strategies may enhance the persistence of MH2-6 in hydrothermal vent environments.