Clostridium spp. – obligately anaerobic pathogens

Most Clostridia lack respiratory chain cytochromes, catalase, peroxidases and superoxide dismutase. They obtain ATP only by substrate-level phosphorylation (in which high energy phosphate bonds from organic intermediates are transferred to ADP). A number of clostridia ferment sugars, producing butyric acid (and also acetone & butanol); others ferment amino acids. Clostridia are ubiquitous in soil and some are part of the normal human flora