This 1978 study investigated the taxonomic relationships among three thermophilic Clostridium species using DNA-DNA hybridization and guanine-plus-cytosine (G+C) content analysis. Researchers compared 13 strains of C. thermohydrosulfuricum, multiple strains of C. thermosaccharolyticum, and two strains of C. tartarivorum isolated from beet sugar factory extracts, along with reference strains of other clostridia and sulfate-reducing bacteria. DNA homology experiments revealed that C. thermohydrosulfuricum strains formed a genotypically homogeneous group clearly distinct from C. thermosaccharolyticum. However, C. tartarivorum strains showed high DNA homology with C. thermosaccharolyticum reference strains, indicating they belong to the same species. G+C content values for the three species ranged from 29-32 mol%, while the structurally similar sulfide-spoilage bacterium Desulfotomaculum nigrificans had significantly higher G+C content (45-46.5 mol%), confirming its genetic distance from these species. The authors proposed establishing E100-69 as the neotype strain for C. thermohydrosulfuricum and recommended merging C. tartarivorum with C. thermosaccharolyticum, treating tartrate-fermenting isolates as a distinct biotype.

Key findings

• C. thermohydrosulfuricum forms a genotypically homogeneous group that is genetically distinct from C. thermosaccharolyticum despite similar biochemical characteristics
• C. tartarivorum strains belong to the C. thermosaccharolyticum group and should be merged as a tartrate-fermenting biotype rather than a separate species
• E100-69 is proposed as the neotype strain for C. thermohydrosulfuricum following loss of the original type strain
• All three Clostridium species share similar G+C content (29-32 mol%), while Desulfotomaculum nigrificans has significantly different G+C content (45-46.5 mol%), confirming genetic separation