The Genus Archaeoglobus
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The Genus Archaeoglobus PATRICIA HARTZELL AND DAVID W. REED
Archeal Sulfate Reducers The domain Archaea contains two genera, thermophilic Archaeoglobus and thermoacidophilic Caldivirga, which obtain energy by reducing oxidized sulfur compounds to H2S under anaerobic conditions. Both Archaeoglobus fulgidus and Caldivirga maquilingensis thrive at 85°C, the optimal temperature for growth (Itoh et al., 1999).
Phylogeny The genus Archaeoglobus is classified in the Archaeoglobaceae family, Archaeoglobales order, Archaeoglobi class, Euryarchaeota phylum, of the domain Archaea (Huber and Stetter, 2001). Archaeoglobus is a chemolithoautotrophic or chemoorganotrophic microorganism using sulfate, sulfite or thiosulfate as electron acceptor, with the formation of hydrogen sulfide as the end product.
Habitat Dissimilatory sulfate-reducers inhabit aquatic and terrestrial sediments and play an essential role in the biogeochemical sulfur cycle. Although oxygen is the most abundant terrestrial element on earth and more electronegative than sulfur, sulfate (an oxidized form of sulfur) is a major anion in anoxic environments in which sulfur predominates (such as seawater) and serves as the electron acceptor for many organisms including Archaeoglobus. Sulfate can be reduced by sulfate-reducers to hydrogen sulfide (H2S), which can be assimilated by other organisms as a substrate for growth. The Archaeoglobus genus contains, to date, four cultured species, A. fulgidus, A. profundus, A. veneficus and A. lithotrophicus. The type strain A. fulgidus VC-16, the first Archaeoglobus species identified, is a chemolithoautotroph that grows preferentially as a chemoorganotroph. It was isolated initially from near anoxic shallow and abyssal submarine hydrothermal vents off
the coast of Italy (Stetter et al., 1987) and later from hot oil field waters in the North Sea (Beeder et al., 1994). In addition to Archaeoglobus fulgidus strain VC-16, strains 7324 and Z have been partially characterized. The chemolithoheterotroph A. profundus obligately requires H2 as an electron donor (Burggraf et al., 1990). Archaeoglobus profundus lacks the carbon monoxide dehydrogenase necessary for CO2 fixation into acetyl-CoA and hence is unable to grow autotrophically (Vorholt et al., 1995). Like A. fulgidus, A. profundus also was isolated from a marine hydrothermal system. Archaeoglobus fulgidus strain Z was isolated from Vulcano (Zellner et al., 1989) and strain 7324 from hot oil field waters off the coast of Norway (Beeder et al., 1994). Archaeoglobus fulgidus and related species, such as A. veneficus, have been identified in mid-Atlantic ridge hydrothermal vents (Reysenbach et al., 2000) and in association with methanogens in the petroleum hydrocarbon-rich Guaymas Basin off the coast of Mexico (Teske et al., 2002). Archaeoglobus veneficus, a black smoker isolate, does not use sulfate as an electron acceptor but can convert sulfite into sulfide (Huber et al., 1997). It is the fastest growing species of the genus Archaeoglobus with a doubli
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