Many basalt-hosted deep-sea hydrothermal vents have mildly reducing, mildly acidic conditions and porous mineral deposits, which makes them ideal habitats for certain microbes that respire metal oxides. At our main study sites, the Endeavour Segment and Axial Volcano on the Juan de Fuca Ridge, hyperthermophilic Fe(III) oxide reducers were cultured from the interior of all five active sulfide structures sampled and were more abundant than hyperthermophilic methanogens. H₂ oxidation coupled with iron reduction, while highly favorable thermodynamically, was presumed to be insignificant in metabolism models due to iron oxide’s insolubility and limited accessibility. However, spectroscopy and petrology analyses of sulfide samples from our study sites show considerable ferric mineral substrates present in pore space surfaces due to seawater intrusion. Hyperthermophilic iron oxide reducers interact with ferrihydrite (Fe(OH)₃) through direct contact via cell wall invaginations and pili attachment. Some hyperthermophiles reduce ferrihydrite to magnetite (Fe₃O₄), perhaps through a maghemite (Fe₂O₃) intermediate. The growth and iron reduction rates of a new hyperthermophilic iron reducer, Hyperthermus strain Ro04, from the Endeavour Segment is being determined for the purpose of quantitatively modeling the growth of these organisms in situ.

By studying the physiology and physical mineral associations and transformations of hyperthermophilic iron reducers and coupling these with maintenance energy calculations, we can begin to model where these processes occur in hydrothermal systems and their impact on biogeochemical processes. Future areas of research include characterizing the nature of hyperthermophile-mineral interactions and transformations using Mӧssbauer, FTIR, and nano-XANES spectroscopies along with electron microprobe and XRD. This will hopefully lead to the determination of biosignatures and the development of in situ sensors for this metabolic process.