Deferribacter abyssi sp. nov., an anaerobic thermophile from deep-sea hydrothermal vents of the Mid-Atlantic Ridge M. L. Miroshnichenko, 1 A. I. Slobodkin, 1 N. A. Kostrikina, 1 S. L’Haridon, 2 O. Nercessian, 2 S. Spring, 3 E. Stackebrandt, 3 E. A. Bonch-Osmolovskaya 1 and C. Jeanthon 2 Correspondence M. L. Miroshnichenko alfamirr@mail.ru 1 Institute of Microbiology, Russian Academy of Sciences, Prospekt 60-letiya Oktyabrya 7/2, Moscow 117811, Russia 2 UMR 6539, Centre National de la Recherche Scientifique and Universite ´ de Bretagne Occidentale, Institut Universitaire Europe ´ en de la Mer, 29280 Plouzane ´ , France 3 DSMZ – Deutsche Sammlung von Mikroorganismen und Zellkulturen, Mascheroder Weg 1b, 38124 Braunschweig, Germany Two strains of thermophilic, anaerobic, chemolithoautotrophic bacteria, designated JR T and DR, were isolated from hydrothermal samples collected on the Mid-Atlantic Ridge from the Rainbow (366 169 N, 336 549 W) and Menez Gwen (376 509 N, 316 509 W) vent fields, respectively. Cells of both isolates were short, straight- to vibrio-shaped, motile rods with one polar flagellum, and were Gram-negative and non-sporulating. Strain JR T was characterized in detail. It was found to grow optimally at pH 6?5–6?7, at 60 6C and in the presence of 30 g NaCl l ”1 . Strain JR T could use molecular hydrogen, acetate, succinate, pyruvate and proteinaceous compounds as electron donors, and elemental sulfur, nitrate or Fe(III) as electron acceptors. No fermentation of organic substrates occurred. The G+C content of the DNA of strain JR T was 30?8 mol%. Strain DR (=DSM 14927) possessed the same morphology and pH, temperature and salinity optima and ranges, and used the same electron acceptors as strain JR T . On the basis of their 16S rDNA sequences (1517 nucleotides), strains JR T and DR were identical and distantly related to Deferribacter thermophilus and Deferribacter desulfuricans (95?3 and 95?2% sequence similarity, respectively). Based on their phenotypic and phylogenetic characteristics, it is proposed that both strains are members of a new species of the genus Deferribacter, for which the name Deferribacter abyssi (type strain JR T =DSM 14873 T =JCM 11955 T ) is proposed. Members of the phylum Deferribacteres are organized into a single class, order and family (Garrity & Holt, 2001). The family Deferribacteraceae (Huber & Stetter, 2002) is composed of three genera, Deferribacter, Flexistipes and Geovibrio, which form one separate lineage on the 16S- rRNA-based phylogenetic tree with sequence similarity values of around 89 %. Currently, the only two species within the genus Deferribacter are Deferribacter thermophilus (Greene et al., 1997) and Deferribacter desulfuricans (Takai et al., 2003). The type species of the genus, D. thermophilus, was isolated from the production water of Beatrice oil field, a high-temperature, sea-water-flooded oil reservoir located in the North Sea, UK. The recently described second species of the genus, D. desulfuricans, was obtained from a deep-sea hydrothermal vent chimney at the Suiyo Seamount in the Izu-Bonin Arc, Japan. Both described species of the genus Deferribacter are strictly anaerobic, thermophilic organisms capable of the oxidation of a variety of complex organic compounds and organic acids in the presence of diverse electron acceptors. In this report, we describe a novel species of this genus, two representatives of which were obtained from two different deep-sea hydrothermal vent fields of the Mid-Atlantic Ridge. Strains JR T and DR were isolated from hydrothermal samples collected in May 2001 at the Rainbow (36 u 169 N, 33 u 549 W) and Menez Gwen (37 u 509 N, 31 u 509 W) vent fields of the Mid-Atlantic Ridge. At Rainbow (at a depth of 2400 m), an in situ growth chamber or vent cap (Reysenbach et al., 2000) designed to concentrate the micro-organisms discharged by hydrothermal emissions was deployed using the hydraulic arm of the remotely operated vehicle (ROV) Victor. After in situ incubation for The GenBank accession numbers for the 16S rDNA sequences of Deferribacter abyssi strains JR T and DR are AJ515882 and AJ515881, respectively. 02673 G 2003 IUMS Printed in Great Britain 1637 International Journal of Systematic and Evolutionary Microbiology (2003), 53, 1637–1641 DOI 10.1099/ijs.0.02673-0