Isolation of a ubiquitous obligate thermoacidophilic archaeon from deep-sea hydrothermal vents

Deep-sea hydrothermal vents play an important role in global biogeochemical cycles, providing biological oases at the seafloor 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 seawater, 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 ecosystem 1. It has been proposed that fluid pH 2 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 rRNA genes from deep-sea hydrothermal deposits have identified a widespread euryarchaeotal lineage, DHVE2 3-6. Despite DHVE2's ubiquity and apparent deep-sea endemism, 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 to 75°C. In addition, we demonstrate that this isolate constitutes up to 15% of the archaeal population, providing the first evidence that thermoacidophiles may be key players in the sulphur and iron cycling at deep-sea vents. Since their discovery in 1977, deep-sea hydrothermal vents have provided one of the only environments on Earth for searching for the upper temperature limits of life; these ecosystems may represent models for both the origin of life on Earth and exploration of life on other planets. This ecosystem, fuelled largely by geochemical energy, hosts many invertebrates new to science, and they often thrive because of their endosymbiotic bacterial partners. Likewise, these deep-sea oases have provided a vast array of newly described free-living microbes, many associated with the actively forming porous deep-sea vent deposits such as 'chimneys'. Here, the contrasting geochemistry of hydrothermal fluids and seawater, the mineralogy of porous substrates, and microbial activity are tightly coupled. The steep chemical and thermal gradients within the walls of the deposits provide a wide range of microhabitats for microorganisms 7. For example, calculations of transport across chimney walls 2 showed that, the pH of fluids (at < 120°C) within pores of chimney's should be very low (pH <3) if only diffusion is occurring. 3 If some advection of seawater into the chimney occurs, the porewater pH at 50 to 80°C should still be …