B. Jochimsen et al.: Stetteria hydrogenophila 67 Extremophiles (1997) 1:67–73 © Springer-Verlag 1997 ORIGINAL PAPER Beate Jochimsen · Susanne Peinemann-Simon Horst Völker · Doris Stüben · Reiner Botz Peter Stoffers · Paul R. Dando · Michael Thomm Stetteria hydrogenophila, gen. nov. and sp. nov., a novel mixotrophic sulfur-dependent crenarchaeote isolated from Milos, Greece Received: September 4, 1996 / Accepted: November 12, 1996 Key words Hyperthermophilic · Crenarchaeota · Hydro- gen and sulfur dependence · Hydrothermal · Stetteria hydrogenophila Marine hyperthermophilic archaea have been isolated from shallow submarine hydrothermal systems and abyssal “black smokers” (Stetter 1992, 1996). The biodiversity of hyperthermophiles in shallow marine hydrothermal sys- tems has been extensively studied at the beaches of Vulcano and Ischia (Italy), off Kodakara-Jima (Japan), and to a lesser extent in Sangeang (Indonesia), Sao Miguel (Azores), and off Iceland (Zillig 1990; Huber et al. 1991; Hokai et al. 1995; Stetter 1996). The communities of hyperthermophiles in hydrothermal systems of the South Aegean volcanic arc have not previously been described. The island of Milos is located in this volcanic zone. Paleohori Bay at Milos is a geothermally active area charac- terized by extensive venting of both gas and hot water (Dando et al. 1995a,b). The venting liquids originating from a reservoir located underneath the seafloor are enriched in Na, K, Ca, and CO 2 compared with seawater, and depleted in Mg and sulfate. This unusual composition of the brine, the high temperature, and the sulfur content of the sedi- ment, together with the efflux of gas, which is mainly CO 2 but contains up to 3% hydrogen, makes this bay a good habitat for the isolation of hyperthermophilic archaea. We report here the isolation and characterization of a novel, heterotrophic hyperthermophile whose growth is strictly dependent upon the presence of hydrogen and elemental sulfur. Materials and methods Collection of samples. Samples from marine sediments at a depth of 10 m were taken in 20-ml syringes by scuba divers at different locations of the white mats overlying hot brine seeps (Dando et al. 1995a) at Paleohori Bay, Milos. These samples were combined and stored in 28-ml serum tubes Abstract A new hyperthermophilic, strictly anaerobic crenarchaeote, Stetteria hydrogenophila DSM11227 representing a new genus within the family of Desulfurococcaceae, was isolated from the sediment of a marine hydrothermal system at Paleohori Bay in Milos, Greece. Cells are gram-negative irregular and disc-shaped cocci, 0.5–1.5 μm in diameter, which are flagellate and can form cytoplasmatic protrusions up to 2 μm in length. The strain grew optimally at 95°C at pH 6.0 and at a NaCl concentration of 3%. The organism grew mixotrophically on peptide substrates. It required elemental sulfur as an external electron acceptor, and in addition, its growth was completely dependent on the presence of molecular hydrogen. Sulfur could be replaced by thiosulfate. H 2 S, CO 2 , acetate, and ethanol were identified as products of metabolism. The G + C content of DNA was 65 mol%. Analysis of its phylogenetic position by sequence analysis of 16S rRNA placed this organism in the family of Desulfurococcaceae. The dependence of this organism on both hydrogen and sulfur during growth on peptide sub- strates distinguishes Stetteria from all previously described species of Crenarchaeota. Communicated by: G. Antranikian B. Jochimsen · S. Peinemann-Simon · H. Völker · M. Thomm () Institut für Allgemeine Mikrobiologie, Universität Kiel, Am Botanischen Garten 1-9, 24118 Kiel, Germany Tel. +49-431-880-4330; Fax +49-431-880-2194 D. Stüben 1 · R. Botz · P. Stoffers Geologisch-Palaäontologisches Institut und Museum, Christian Albrechts Universität zu Kiel, Germany P.R. Dando 2 Marine Biological Association of the United Kingdom, Plymouth, UK Present address: 1 Institut für Petrographie und Geochemie, Universität Karlsruhe, Kaiserstrasse 12, 76128 Karlsruhe, Germany 2 School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Gwynedd LL59 5EY, UK