Chemoautotrophy
Chemoautotrophs grow by powering CO₂ fixation with the energy released by the oxidation of a smorgasbord of redox substrates. Electron donors utilized by these organisms include reduced sulfur (H₂S, S₂O₃^-2, S°, etc.), reduced iron (e.g., Fe⁺², pyrite), reduced nitrogen (NH₃, NO₂^-) and H₂ (Kuenen and Bos, 1989), while O₂, NO₃^-, SO₄^-2, and Fe⁺³ can serve as electron acceptors (Kelly and Wood, 2001). By coupling the oxidation and reduction of inorganic compounds to the generation of biomass, the activities of these organisms tie the geochemical cycle of their redox substrates to the carbon, nitrogen, and phosphorus cycles. Further, at H₂S, Fe⁺², and H₂-rich deep-sea hydrothermal vents and cold seeps, free-living and symbiotic sulfur-oxidizing chemoautotrophs are dominant primary producers (Jannasch, 1979).

Sulfur oxidation
The bacteria of the oxidative part of the sulfur cycle are of global importance and catalyze complex pathways for the complete oxidation of sulfide to sulfate. One of the important groups catalyzing the oxidation of reduced sulfur compounds in the marine environment are bacteria belonging to the genus Thiomicrospira, a group which originally included all marine, spiral-shaped sulfur oxidizing bacteria. Subsequent analyses of 16S rDNA sequences have revealed the polyphyletic nature of this group; members of Thiomicrospira are distributed among the gamma and epsilon subdivisions of the Proteobacteria. All Thiomicrospira species characterized to date are obligate chemolithoautotrophic bacteria that use sulfide, thiosulfate, and elemental sulfur as electron donors, and CO₂ as their carbon source. Two organisms (gamma and epsilon-Proteobacteria) have been selected to embrace the phylogenetic breadth of proteobacterial chemoautotrophs

Thiomicrospira crunogena
The gamma-Proteobacterium T. crunogena is cosmopolitan. Originally isolated from the East Pacific Rise (Jannasch et al., 1985), it was subsequently cultivated or detected with molecular methods from deep-sea vents in both the Pacific and Atlantic (Wirsen et al., 1998). Further, closely related species have been found at shallow-water hydrothermal vents (Muyzer et al., 1995; Brinkhoff et al., 1999). It has a remarkably high growth rate for a chemoautotroph (Jannasch et al., 1985).


References

Brinkhoff, T., Sievert, S.M., Kuever, J., and Muyzer, G. (1999) Distribution and diversity of sulfur-oxidizing Thiomicrospira spp. at a shallow-water hydrothermal vent in the Aegean Sea (Milos, Greece). Appl. Environ. Microbiol. 65: 3843-3849.

Huber, J., Butterfield, D.A., and Baross, J.A. (2003) Bacterial diversity in a subseafloor habitat following a deep-sea volcanic eruption. FEMS Microbiol. Ecol. 43: 393-409.