Deep-sea hydrothermal vents are important in global biogeochemical cycles, providing biological oases at the sea floor that are supported by the thermal and chemical flux from the Earth's interior. As hot, acidic and reduced hydrothermal fluids mix with cold, alkaline and oxygenated sea water, minerals precipitate to form porous sulphide–sulphate deposits. These structures provide microhabitats for a diversity of prokaryotes that exploit the geochemical and physical gradients in this dynamic ecosystem¹. It has been proposed that fluid pH in the actively venting sulphide structures is generally low (pH < 4.5)², yet no extreme thermoacidophile has been isolated from vent deposits. Culture-independent surveys based on ribosomal RNA genes from deep-sea hydrothermal deposits have identified a widespread euryarchaeotal lineage, DHVE2 (deep-sea hydrothermal vent euryarchaeotic 2)^{3, 4, 5, 6}. Despite the ubiquity and apparent deep-sea endemism of DHVE2, cultivation of this group has been unsuccessful and thus its metabolism remains a mystery. Here we report the isolation and cultivation of a member of the DHVE2 group, which is an obligate thermoacidophilic sulphur- or iron-reducing heterotroph capable of growing from pH 3.3 to 5.8 and between 55 and 75 °C. In addition, we demonstrate that this isolate constitutes up to 15% of the archaeal population, providing evidence that thermoacidophiles may be key players in the sulphur and iron cycling at deep-sea vents.

1. Department of Biology, Portland State University, Portland, Oregon 97201, USA
2. Department of Molecular & Cellular Biology, University of Guelph, Guelph, Canada
3. US Geological Survey, MS 430, 12201 Sunrise Valley Drive, Reston, Virginia 20192, USA
4. Department of Marine Biogeochemistry & Toxicology, Royal Netherlands Institute for Sea Research, 1790 AB Den Burg, Texel, The Netherlands
5. Department of Marine Chemistry and Geochemistry, WHOI, Woods Hole, Massachusetts 02543, USA
6. Complex Systems Research Center, EOS, University of New Hampshire, 366 Morse Hall, 39 College Road, Durham, New Hampshire 03824-3525, USA

Correspondence to: Anna-Louise Reysenbach¹ Correspondence and requests for materials should be addressed to A.-L.R. (Email: reysenbacha@pdx.edu). The new sequences described in this manuscript have been deposited in GenBank, accession numbers DQ451875 (T469) and DQ451876 (T449).

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