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Two thermophilic, Gram-stain-positive, rod-shaped, non-spore-forming bacteria (strains KI3T and KI4T) were isolated from geothermally heated biofilms growing on a tumulus in the Kilauea Iki pit crater on the flank of Kilauea Volcano (Hawai'i, USA). Strain KI3T grew over an examined temperature range of 50-70 °C (no growth at 80 °C) and a pH range of 6.0-9.0, with optimum growth at 70 °C and pH 7.0. Strain KI4T grew at temperatures of 55-70 °C and a pH range of 5.8-8.0, with optimum growth at 65 °C and pH 6.7-7.1. The DNA G+C contents of strains KI3T and KI4T were 66.0 and 60.7 mol%, respectively. The major fatty acid for both strains was 12-methyl C18: 0. Polar lipids in strain KI3T were dominated by glycolipids and phosphatidylinositol, while phosphatidylinositol and phosphoglycolipids dominated in strain KI4T. Strain KI3T oxidized carbon monoxide [6.7±0.8 nmol CO h-1 (mg protein)-1], but strain KI4T did not. 16S rRNA gene sequence analyses determined that the strains belong to the class Thermomicrobia, and that strains KI3T and KI4T are related most closely to Thermomicrobium roseum DSM 5159T (96.5 and 91.1 % similarity, respectively). 16S rRNA gene sequence similarity between strain KI3T and strain KI4T was 91.4 %. Phenotypic features and phylogenetic analyses supported the affiliation of strain KI3T to the genus Thermomicrobium, while results of chemotaxonomic, physiological and biochemical assays differentiated strains KI3T and KI4T from Thermomicrobium roseum. Strain KI3T (= DSM 27067T = ATCC BAA-2535T) is thus considered to be the type strain of a novel species, for which the name Thermomicrobium carboxidumsp. nov. is proposed. Additionally, the characterization and phylogenetic position of strain KI4T showed that it represents a novel species of a new genus, for which the name Thermorudis peleae gen. nov., sp. nov. is proposed. The type strain of Thermorudis peleae is KI4T (= DSM 27169T = ATCC BAA-2536T). © 2014 IUMS.

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International Journal of Systematic and Evolutionary Microbiology

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