Caloribacterium cisternae gen. nov., sp. nov., an anaerobic thermophilic bacterium from an underground gas storage reservoir G. B. Slobodkina, 1 T. V. Kolganova, 2 N. A. Kostrikina, 1 E. A. Bonch-Osmolovskaya 1 and A. I. Slobodkin 1 Correspondence Galina Slobodkina gslobodkina@mail.ru 1 Winogradsky Institute of Microbiology, Russian Academy of Sciences, Prospect 60-letiya Oktyabrya 7/2, 117312 Moscow, Russia 2 Bioengineering Center, Russian Academy of Sciences, Prospect 60-letiya Oktyabrya 7/1, 117312 Moscow, Russia A novel anaerobic, moderately thermophilic bacterium (strain SGL43 T ) was isolated from Severo- Stavropolskoye underground gas storage reservoir (Russia). Cells of strain SGL43 T were motile straight rods, 0.4 mm in diameter and 2.0–3.0 mm in length. The temperature range for growth was 28–65 6C, with optimum growth at 50 6C. The pH range for growth was 5.5–8.0, with optimum growth at pH 7.0–7.5. Growth of strain SGL43 T was observed at NaCl concentrations of 0–4.0 % (w/v) with optimum growth at 1.0 % (w/v) NaCl. Substrates utilized by strain SGL43 T included peptone, yeast extract, glucose, fructose, maltose, galactose, pyruvate and citrate. Products of glucose or citrate fermentation were acetate, hydrogen and CO 2 . Thiosulfate was reduced to sulfide. The DNA G+C content of strain SGL43 T was 43.1 mol%. 16S rRNA gene sequence analysis revealed that strain SGL43 T belongs to the order Thermoanaerobacterales (phylum ‘Firmicutes’). The closest relative of strain SGL43 T was Thermoanaerobacterium saccharolyticum (86.2 % 16S rRNA gene sequence similarity with the type strain). Based on the data presented here, strain SGL43 T is considered to represent a novel species of a new genus, for which the name Caloribacterium cisternae gen. nov., sp. nov. is proposed. The type strain of Caloribacterium cisternae, the type species of the genus, is SGL43 T (5DSM 23830 T 5VKM B-2670 T ). Underground reservoirs for the storage of natural gas represent anthropogenic, carbon-rich environments that are often characterized by elevated temperatures. The microbial communities of these habitats have been poorly studied. The presence of viable methanogenic, acetogenic, sulfate-, nitrate- and iron-reducing, fermentative mesophilic prokaryotes has been demonstrated for deep subsurface gas storage reservoirs in Russia and France. Both culturing and molecular techniques have shown that members of the ‘Firmicutes’ and ‘Proteobacteria’ dominate the bacterial portions of the community (Ivanova et al., 2007; Basso et al., 2009). To our knowledge, only one thermophilic anaerobic micro-organism, ‘Moorella perchloratireducens’ (strain An105ATCC BAA-15315JCM 14829), has been isolated from an underground gas storage reservoir (Balk et al. 2008). Here, we report the isolation and characteri- zation of a novel anaerobic, moderately thermophilic, organotrophic bacterium (strain SGL43 T ) from production water of Severo-Stavropolskoye (North Caucasus Region, Russia), the world’s largest such reservoir. Details of the sampling location and procedures are described by Ivanova et al. (2007). An enrichment culture was initiated by inoculation of 10 % (w/v) of the water sample into anaerobically prepared, bicarbonate-buffered, sterile (135 u C, 1 h) liquid medium of the following composition (per litre distilled water): 0.33 g NH 4 Cl, 0.33 g KCl, 0.33 g MgCl 2 . 6H 2 O, 0.33 g CaCl 2 , 0.33 g KH 2 PO 4 , 2.0 g NaHCO 3 , 1 ml trace element solution (Slobodkin et al., 1997), 1 ml vitamin solution (Wolin et al., 1963) and 0.2 g yeast extract (Sigma). The medium did not contain any reducing agents; the pH of the auto- claved medium was 6.7–6.9 at 20 uC. Glucose (15 mM) was added as substrate from anaerobically prepared sterile stock solution before inoculation. Incubation temperature was 50 u C. After three subsequent transfers, the enrichment was purified by serial 10-fold dilutions in the same medium followed by the selection of well-separated colonies that had developed in anaerobic agar blocks (1.5 % agar in The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain SGL43 T is JF262044. A supplementary table is available with the online version of this paper. International Journal of Systematic and Evolutionary Microbiology (2012), 62, 1543–1547 DOI 10.1099/ijs.0.033076-0 033076 G 2012 IUMS Printed in Great Britain 1543