ABSTRACT
The genus Clostridium is composed of spore-forming anaerobic rods. Spore-forming anaerobic cocci — the genus Sporosarcina - have been described, but we know very little about them. The genus Desulfotomaculum also contains anaerobic sporing rods, but these may be differentiated from the clostridia by a combination of three characteristics:3 (1) Gram-negativity; (2) DNA base composition, GC = 41 to 46%; and (3) cytochrome of the protoheme class. Some members of Clostridium, especially the cellulose-fermenters, are Gram-negative; others have DNA with GC = 43 to 46%; in still others, cytochromes have been found. However, the most important characteristic shared by organisms in Desulfotomaculum is their ability to reduce sulfate to sulfide, a characteristic uncommon among strains of Clostridium. Of the three species of Desulfotomaculum, D. nigrificans is thermophilic. The two mesophilic species can be differentiated by the ability of D. ruminis to grow in formate and sulfate and the inability of D. orientis to do so.
