A thermophilic, aerobic, Gram-stain-positive bacterium (strain PM5T), which formed mycelia of irregularly branched filaments and produced multiple exospores per cell, was isolated from a geothermally heated biofilm. Strain PM5T 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 PM5T belonged to the class Ktedonobacteria , and was related most closely to Thermogemmatispora onikobensis ONI-1T (97.7 % similarity) and Thermogemmatispora foliorum ONI-5T (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 PM5T to the genus Thermogemmatispora . Strain PM5T 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 PM5T from the two recognized species of the genus Thermogemmatispora . Strain PM5T differed from Thermogemmatispora onikobensis ONI-1T 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 PM5T is therefore considered to represent a novel species, for which the name Thermogemmatispora carboxidivorans sp. nov. is proposed. The type strain is PM5T ( = DSM 45816T = ATCC BAA-2534T).