A thermophilic, aerobic, Gram-stain-positive bacterium (strain PM5(T)), which formed mycelia of irregularly branched filaments and produced multiple exospores per cell, was isolated from a geothermally heated biofilm. Strain PM5(T) grew at 40-65 °C and pH 4.1-8.0, with optimal growth at 55 °C and pH 6.0. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain PM5(T) belonged to the class Ktedonobacteria, and was related most closely to Thermogemmatispora onikobensis ONI-1(T) (97.7 % similarity) and Thermogemmatispora foliorum ONI-5(T) (96.1 %). Morphological features and fatty acid profiles (major fatty acids: iso-C17 : 0, iso-C19 : 0 and 12,17-dimethyl C18 : 0) supported the affiliation of strain PM5(T) to the genus Thermogemmatispora. Strain PM5(T) oxidized carbon monoxide [CO; 10±1 nmol h(-1) (mg protein)(-1)], but did not grow with CO as a sole carbon and energy source. Results from analyses of related strains indicated that the capacity for CO uptake occurred commonly among the members of the class Ktedonobacteria; 13 of 14 strains tested consumed CO or harboured coxL genes that potentially enabled CO oxidation. The results of DNA-DNA hybridization and physiological and biochemical tests allowed the genotypic and phenotypic differentiation of strain PM5(T) from the two recognized species of the genus Thermogemmatispora. Strain PM5(T) differed from Thermogemmatispora onikobensis ONI-1(T) in its production of orange pigment, lower temperature optimum, hydrolysis of casein and starch, inability to grow with mannitol, xylose or rhamnose as sole carbon sources, and utilization of organic acids and amino acids. Strain PM5(T) is therefore considered to represent a novel species, for which the name Thermogemmatispora carboxidivorans sp. nov. is proposed. The type strain is PM5(T) ( = DSM 45816(T) = ATCC BAA-2534(T)).