Summary auto-generated
This study describes the isolation and characterization of Thermaerobacter subterraneus sp. nov., a novel strictly aerobic, thermophilic bacterium recovered from sediment samples in the Great Artesian Basin (GAB) of Australia. The isolate, designated C21T, was obtained from an outflow channel of a geothermal bore with water temperatures reaching 88°C. The bacterium is rod-shaped, Gram-positive (though staining Gram-negative), spore-forming, and grows optimally at 70°C and pH 8.5. It is strictly heterotrophic, requiring only yeast extract and/or tryptone for growth and unable to utilize carbohydrates, organic acids, or other substrates. Phylogenetic analysis of the 16S rRNA gene places C21T within the phylum Firmicutes as a member of the order Clostridiales, with Thermaerobacter marianensis as its closest relative (98% similarity). However, C21T and T. marianensis differ significantly in physiological properties and show less than 5% DNA-DNA hybridization, supporting their designation as separate species. The genomic DNA G+C content is 71 mol%. The genus Thermaerobacter was emended to accommodate both spore-forming and non-spore-forming aerobic thermophiles.
Key findings
- Thermaerobacter subterraneus is a novel strictly aerobic, thermophilic, spore-forming bacterium isolated from the Great Artesian Basin of Australia, growing optimally at 70°C and pH 8.5
- The bacterium is strictly heterotrophic, utilizing only yeast extract and tryptone as carbon sources, showing no growth on carbohydrates, organic acids, or other tested substrates
- 16S rRNA analysis shows 98% similarity to Thermaerobacter marianensis, but less than 5% DNA-DNA hybridization and distinct physiological differences warrant species separation
- The genus Thermaerobacter was emended to encompass aerobic thermophiles that may or may not produce spores, with genomic DNA G+C content of 71-73 mol%
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Abstract
A strictly aerobic, thermophilic, Gram-positive, spore-producing, rod-shaped bacterium (2.0--10.0 x 0.3 microm), designated isolate C21(T), 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 C21(T) 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 C21(T) placed it as a member of the phylum Firmicutes, with Thermaerobacter marianensis as the closest relative (similarity value of 98%). However, isolate C21(T) 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 C21(T) be designated Thermaerobacter subterraneus sp. nov. (type strain C21(T)=ATCC BAA-137(T)=DSM 13965(T)).