Sulfur oxidation at deep-sea hydrothermal vents

Microbial oxidation of geothermally produced reduced sulfur compounds is at the nexus of the biogeochemical carbon and sulfur cycles at deep-sea hydrothermal vents. Available information indicates that microbial symbionts and free-living gammaproteobacteria of the genera Thiomicrospira, Halothiobacillus, and Beggiatoa are important sulfur-oxidizers above the seafloor at these systems. In addition, bacteria belonging to the Epsilonproteobacteria have been identified as a major component of microbial communities at deep-sea vents. We have previously identified a novel sulfur-oxidizing epsilonproteobacterium, Candidatus Arcobacter sulfidicus, which produces sulfur in filamentous form that is morphologically and chemically similar to material observed before and after submarine volcanic eruptions. In the meantime, many autotrophic epsilonproteobacteria have been isolated and characterized from deep-sea vents, providing further evidence that these organisms play an important role in sulfur and carbon cycling in these environments. These kinds of bacteria may form an important component of a subseafloor biosphere, a currently poorly defined, yet potentially critical component of deep-sea hydrothermal vents. Many autotrophic bacteria and archaea occurring at deep-sea hydrothermal vents, including epsilonproteobacteria, use the reductive tricarboxylic acid cycle for autotrophic carbon fixation, questioning the paradigm of the Calvin-Benson-Bassham cycle being at the base of the food web of these ecosystems. In the future, integrated geochemical and biological studies are needed to further advance our understanding of chemoautotrophic sulfur oxidation at deep-sea vents, which will be greatly facilitated by having the genomes of representative sulfur-oxidizing bacteria available.