Transfer of thermobacteroides leptospartum and Clostridium thermolacticum as Clostridium stercorarium subsp. leptospartum subsp. thermolacticum subsp. nov., comb. nov. and C. stercorarium subsp. thermolacticum subsp. nov., comb. nov.

16S rRNA sequencing and sequence analysis of the sole member of the genus Thermobacteroides, Thermobacteroides leptospartum, revealed that it was related to members of cluster III (according to the scheme of Collins et al. 1994) represented exclusively by cellulolytic Clostridium species. Phenotypic studies indicated that Thermobacteroides leptospartum was also able to grow on cellulose, providing further evidence of its affiliation to members of cluster III. Its closest phylogenetic relatives, Clostridium thermolacticum and Clostridium stercorarium, were almost equidistantly placed with a similarity value of 99%. DNA hybridization studies also indicated that Thermobacteroides leptospartum, C. thermolacticum and C. stercorarium were closely related to each other (values of over 95% homology). Similarities based on the comparison of the 16S rRNA gene sequences and DNA homology are sufficiently high to regard all three strains as subspecies of a single species. It is therefore proposed that Thermobacteroides leptospartum and C. thermolacticum be transferred to cluster III as C. stercorarium subsp. leptospartum subsp. nov., comb. nov. and C. stercorarium subsp. thermolacticum subsp. nov., comb. nov., respectively, thus automatically creating C. stercorarium subsp. stercorarium subsp. nov., comb. nov. The transfer of the sole member of Thermobacteroides invalidates the taxonomic status of the genus.