Obligate aerobes - Use an O2-dependent system to generate ATP. Examples include Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bacillus.
Obligate anaerobes - Examples include Clostridium, Bacteroides, and Actinomyces. They lack catalase and/or superoxide dismutase and are thus susceptible to oxidative damage. Generally foul smelling (short-chain fatty acids), are difficult to culture, and produce gas in tissue (CO2 and H2).