Thermoanaerobacterium aciditolerans sp. nov., a moderate thermoacidophile from a Kamchatka hot spring

1 Institute of Microbiology, Russian Academy of Sciences, Prospekt 60-Letiya Oktyabrya 7/2, Moscow 117312, Russia 2 Bioengineering Center, Russian Academy of Sciences, Prospect 60-Letiya Oktyabrya 7/1, 117312 Moscow, Russia 3 Department of Microbiology, University of Georgia, Athens, GA, USA Correspondence I. V. Kublanov kublanov.ilya{at}gmail.com An anaerobic, moderately thermoacidophilic bacterium, strain 761-119 T , was isolated from an acidic hot spring in the Orange Field of the Uzon Caldera (Kamchatka, far-eastern Russia). Cells were spore-forming, Gram-positive rods, possessing one polar flagellum. Growth of strain 761-119 T was observed between 37 and 68 °C and in the pH 20 °C range 3.2–7.1. No growth was observed within 5 days of incubation at or below 35 °C and at or above 70 °C, as well as at or below pH 20 °C 2.8 and at or above pH 20 °C 7.5. The optimal temperature and pH 20 °C for growth were 55 °C and pH 20 °C 5.7, respectively. A wide range of carbohydrates and polysaccharides were fermented, as well as peptides and proteinaceous substrates. The main products of glucose fermentation were acetate, ethanol, lactate, H 2 and CO 2 . The DNA G+C content was 34 (±0.5) mol%. 16S rRNA gene sequence analysis indicated that strain 761-119 T belonged to the genus Thermoanaerobacterium . The level of 16S rRNA gene sequence similarity with other Thermoanaerobacterium species was 86.5–97.8 %, with the only moderately acidophilic member of this genus, Thermoanaerobacterium aotearoense , being one of its closest relatives. DNA–DNA hybridization with T. aotearoense showed 33 % relatedness. Thus, morphological (one polar flagellum) and physiological characteristics (lower pH limit of growth at pH 20 °C 3.2 compared with T. aotearoense ) and 16S rRNA gene sequence analyses revealed that strain 761-119 T represents a novel species in the genus Thermoanaerobacterium , for which the name Thermoanaerobacterium aciditolerans sp. nov. is proposed, with the type strain 761-119 T (=DSM 16487 T =VKM B-2363 T ). The GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain 761-119 T is AY350594 .