Thermomicrobium carboxidum sp nov., and Thermorudis peleae gen. nov., sp nov., carbon monoxide-oxidizing bacteria isolated from geothermally heated biofilms

Two thermophilic, Gram-stain-positive, rod-shaped, non-spore-forming bacteria (strains Kl3(T) and Kl4(T)) were isolated from geothermally heated biofilms growing on a tumulus in the Kilauea lki pit crater on the flank of Kilauea Volcano (Newell, USA). Strain Kl3T grew over an examined temperature range of 50-70 degrees C (no growth at 80 degrees C) and a pH range of 6.0-9.0, with optimum growth at 70 degrees C and pH 7.0. Strain Kl4(T) grew at temperatures of 55-70 degrees C and a pH range of 5.8-8.0, with optimum growth at 65 degrees C and pH 6.7-7.1. The DNA G+C contents of strains Kl3(T) and Kl4(T) were 66.0 and 60.7 mol%, respectively. The major fatty acid for both strains was 12-methyl C-18:0. Polar lipids in strain Kl3(T) were dominated by glycolipids and phosphatidylinositol, while phosphatidylinositol and phosphoglycolipids dominated in strain Kl4(T). Strain Kl3(T) oxidized carbon monoxide [6.7 +/- 0.8 nmol CO h(-1) (mg protein)(-1)], but strain Kl4(T) did not. 16S rRNA gene sequence analyses determined that the strains belong to the class Thermomicrobia, and that strains Kl3(T) and Kl4(T) are related most closely to Thermomicrobium roseum DSM 5159(T) (96.5 and 91.1 % similarity, respectively). 16S rRNA gene sequence similarity between strain Kl3T and strain Kl4(T) was 91.4%. Phenotypic features and phylogenetic analyses supported the affiliation of strain Kl3(T) to the genus Thermomicrobium, while results of chemotaxonomic, physiological and biochemical assays differentiated strains Kl3(T) and Kl4(T) from Thermomicrobium roseum. Strain Kl3(T) (=DSM 27067(T)=ATCC BAA-2535(T)) is thus considered to be the type strain of a novel species, for which the name Thermomicrobium carboxidum sp. nov. is proposed. Additionally, the characterization and phylogenetic position of strain Kl4(T) 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 Kl4(T) (=DSM 27169(T)=ATCC BAA-2536(T)).