In this field, primarely information about how the bacterium is utilizing oxygen in its metabolism, is given. The following alternatives exists:
- Aerobic means that the bacterium needs oxygen for growth (and to multiply).
- Facultatively aerobic (= facultatively anaerobic) means that the bacterium can utilize oxygen if it is present, but that they also grow and multiply in the absence of oxygen, because they can adapt their metabolism to different conditions. (Facultatively) aerobic means that the bacterium mainly has aerobic metabolism, but that it can also grow slowly under anaerobic conditions.
- Microaerophilic means that the bacterium needs oxygen for growth, but that it cannot withstand normal concentrations of oxygen.
- Anaerobic means that the bacterium does not utilize oxygen, which is poisonous for the bacterium.
- Aerotolerant means that the bacterium has an anaerobic metabolism (does not utilize oxygen), but it is not poisoned by oxygen.
- (Capnophilic means tht the growth of the microorganism is stimulated by CO2. The underlaying metabolic reason is not clear.)