Caldicoprobacter guelmensis sp. nov., a thermophilic, anaerobic, xylanolytic bacterium isolated from a hot spring.

A hyperthermophilic anaerobic bacterium, designated D2C22(T), was isolated from the hydrothermal hot spring of Guelma in north-east Algeria. The isolate was a Gram-stain-positive, non-sporulating, non-motile rod, appearing singly or in pairs (0.3-0.4 × 8.0-9.0 µm). Strain D2C22(T) grew anaerobically at 45-85 °C (optimum 65 °C), at pH 5-9 (optimum pH 6.8) and with 0-20 g NaCl l(-1). Strain D2C22(T) used glucose, galactose, lactose, fructose, ribose, xylose, arabinose, maltose, cellobiose, mannose, melibiose, sucrose, xylan and pyruvate (only in the presence of yeast extract or biotrypticase) as electron donors. The end products from glucose fermentation were acetate, lactate, CO2 and H2. Nitrate, nitrite, thiosulfate, elemental sulfur, sulfate and sulfite were not used as electron acceptors. The predominant cellular fatty acids were iso-C15:0 and iso-C17:0. The DNA G+C content was 41.6 mol%. Phylogenetic analysis of the 16S rRNA gene sequence indicated that strain D2C22(T) was most closely related to Caldicoprobacter oshimai JW/HY-331(T), Caldicoprobacter algeriensis TH7C1(T) and Acetomicrobium faecale DSM 20678(T) (95.5, 95.5 and 95.3% 16S rRNA gene sequence similarity, respectively). Based on phenotypic, phylogenetic and chemotaxonomic characteristics, strain D2C22(T) is proposed to be a representative of a novel species of the genus Caldicoprobacter within the order Clostridiales, for which the name Caldicoprobacter guelmensis sp. nov. is proposed. The type strain is D2C22(T) (=DSM 24605(T)=JCM 17646(T)).