A strictly aerobic, thermophilic, gram-positive, spore-producing, rod-shaped bacterium (2.0-10.0 x 0.3 microm), designated isolate C21T, was isolated from a sample collected from an open drain run-off channel of a bore in the Great Artesian Basin of Australia (New Lorne Bore, registered number 17263). Isolate C21T grew optimally at 70 degrees C (temperature range for growth was 55-80 degrees C) and pH 8.5 (pH range for growth was 6.0-10.5), with a generation time of 90 min. The isolate was strictly heterotrophic and grew on yeast extract and/or tryptone as carbon and energy sources. An increase in growth was not observed with carbohydrates (sucrose, cellobiose, glucose, dextrin, amylopectin, chitin, carboxymethylcellulose, xylan, inositol, arabinose, mannose, fructose, gelatin, starch, amylose, galactose, dextrose, xylose, maltose, L-sorbose or raffinose), organic acids (lactic acid, pyruvic acid or benzoic acid) or Casamino acids as sole carbon sources or in the presence of yeast extract and/or tryptone. The G+C content of the chromosomal DNA, as measured by the thermal denaturation method, was 71 mol%. Phylogenetic analysis of the 16S rRNA gene of isolate C21T placed it as a member of the phylum Firmicutes, with Thermaerobacter marianensis as the closest relative (similarity value of 98%). However, isolate C21T and T. marianensis differed in a number of key physiological and phenotypic properties and also had a DNA-DNA hybridization value of less than 5%. Based on this evidence, it is proposed that strain C21T be designated Thermaerobacter subterraneus sp. nov. (type strain C21T = ATCC BAA-137T = DSM 13965T).


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