Caldanaerobacter uzonensis sp. nov., an anaerobic, thermophilic, heterotrophic bacterium isolated from a hot spring Irina V. Kozina, 1 Ilya V. Kublanov, 1 Tatyana V. Kolganova, 2 Nikolai A. Chernyh 1 and Elizaveta A. Bonch-Osmolovskaya 1 Correspondence Ilya V. Kublanov kublanov.ilya@gmail.com 1 Winogradsky Institute of Microbiology Russian Academy of Sciences, Prospekt 60-Letiya Oktyabrya 7/2, 117312 Moscow, Russia 2 Bioengineering Center, Russian Academy of Sciences, Prospekt 60-Letiya Oktyabrya 7/1, 117312 Moscow, Russia An anaerobic thermophilic bacterium, strain K67 T , was isolated from a terrestrial hot spring of Uzon Caldera, Kamchatka Peninsula. Analysis of the 16S rRNA gene sequence revealed that the novel isolate belongs to the genus Caldanaerobacter, with 95 % 16S rRNA gene sequence similarity to Caldanaerobacter subterraneus subsp. subterraneus SEBR 7858 T , suggesting that it represents a novel species of the genus Caldanaerobacter. Strain K67 T was characterized as an obligate anaerobe, a thermophile (growth at 50–75 6C; optimum 68–70 6C), a neutrophile (growth at pH 25 6C 4.8–8.0; optimum pH 25 6C 6.8) and an obligate organotroph (growth by fermentation of various sugars, peptides and polysaccharides). Major fermentation products were acetate, H 2 and CO 2 ; ethanol, lactate and L-alanine were formed in smaller amounts. Thiosulfate stimulated growth and was reduced to hydrogen sulfide. Nitrate, sulfate, sulfite and elemental sulfur were not reduced and did not stimulate growth. Thus, according to the strain’s phylogenetic position and phenotypic novelties (lower upper limit of temperature range for growth, the ability to grow on arabinose, the inability to reduce elemental sulfur and the formation of alanine as a minor fermentation product), the novel species Caldanaerobacter uzonensis sp. nov. is proposed, with the type strain K67 T (5DSM 18923 T 5VKM B-2408 T ). The thermophilic bacteria currently assigned to the genus Caldanaerobacter (Fardeau et al., 2004) were initially described as Thermoanaerobacter subterraneus (Fardeau et al., 2000), Thermoanaerobacter yonseiensis (Kim et al., 2001) and Thermoanaerobacter tengcongensis (Xue et al., 2001), which were isolated from deep-subsurface thermal habitats, and as Carboxydibrachium pacificum (Sokolova et al., 2001), which was obtained from a deep-sea hydrothermal vent. Described almost simultaneously, these species were not compared with each other and, thus, they were classified either as novel Thermoanaerobacter species or within the novel genus Carboxydibrachium. Subsequently, however, they were found to form a separate phylogenetic branch in the genus Thermoanaerobacter (Subbotina et al., 2003) and so were assigned to a new genus Caldanaerobacter (Fardeau et al., 2004). DNA–DNA hybridization showed that they all belonged to the same species Caldanaerobacter subterraneus; thus, they were reclassified into different subspecies (Fardeau et al., 2004). Here, we report the isolation of a new representative of the genus Caldanaerobacter, strain K67 T , from the terrestrial Thermophilny hot spring of the Uzon Caldera (54 u 499 N 160 u 019 E) on the Kamchatka Peninsula (Russian Far East). Strain K67 T was obtained from a cyanobacterial mat sample (50–72 u C; pH 25 uC 6.5–8.2). The isolation proced- ure was accomplished on the following mineral medium (l 21 ): 0.33 g KCl, 0.33 g NH 4 Cl, 0.33 g KH 2 PO 4 , 0.33 g MgCl 2 . 6H 2 O, 0.33 g CaCl 2 . 2H 2 O, 0.5 g NaHCO 3 and 0.5 g Na 2 S . 9H 2 O. The medium was supplemented with 1 g yeast extract l 21 (Difco) as the growth factor, 0.001 g resazurin l 21 as an indicator of anaerobiosis and solutions (1 ml l 21 ) of trace elements (Kevbrin & Zavarzin, 1997) and vitamins (Wolin et al., 1963). High-melting-point agarose (1.5 %, w/v, MP; Boehringer Mannheim) was added as the growth substrate. Anaerobically prepared 10 % (v/v) slurry of the sample (0.5 ml) was placed on top of the agarose block in a Hungate tube. After 3 days of incubation at 55 u C, the upper part of the block became liquid and turbid. Transfer to a semi-liquid medium with 0.5 % (w/v) agarose yielded white colonies after 2–4 days of incubation at the same temperature. Isolated colonies were transferred into the medium with 0.2 % (w/v) galactose. The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain K67 T is EF195126. International Journal of Systematic and Evolutionary Microbiology (2010), 60, 1372–1375 DOI 10.1099/ijs.0.012328-0 1372 012328 G 2010 IUMS Printed in Great Britain