Classification of organisms based on O2 utilization
1. Utilization of O2 during metabolism yields toxic by-products including O2-, singlet oxygen (1O2) and/or H2O2
2. Toxic O2 products can be converted to harmless substances if the organism has catalase (or peroxidase) and superoxide dismutase (SOD)
3. SOD converts O2- into H2O2 and O2
4. Catalase breaks down H2O2 into H2O and O2
5. Any organism that can live in or requires O2 has SOD and catalase (peroxidase)