Thermoleophilum album and Thermoleophilum minutum are culturable representatives of group 2 of the Rubrobacteridae (Actinobacteria).

Analysis of the morphological and genotypic properties of three obligately thermophilic strains of Thermoleophilum album and Thermoleophilum minutum, originally described as green non-sulfur bacteria, indicates that these taxa belong to the Rubrobacter subdivision of the Actinobacteria. EM of the cell wall clearly showed morphology typical of Gram-positive bacteria. A comparison of 16S rRNA gene sequences, including signature nucleotide pairs and secondary structural features considered diagnostic for the subclass Rubrobacteridae, revealed that the three strains of Thermoleophilum were highly similar and should be considered as members of group 2 of this subclass, represented up to now only by uncultured organisms.