An anaerobic organism's any organism that doesn't require oxygen for growth and may even die in its presence. Classification Obligate anaerobes will die when exposed to atmospheric levels of oxygen. Facultative anaerobes can use oxygen when it's present. Aerotolerant organisms can survive in the presence of oxygen, but are anaerobic because they don't use oxygen as a terminal electron acceptor. Microaerophiles are organisms that use oxygen, but only low concentrations (low micromolar range);… (More on Anaerobe)