Abstract
Oxygen (O2) comprises 21% of the atmospheric gases and can permeate into the soil by dissolving in water. An ecosystem where absolute anoxic environment is sustained is a rarity in nature, because the gas–liquid phase on earth is constantly circulating by convection. Hence, all living organisms that are currently living inhabit the earth because of evolution and by adapting to O2, which has high reactivity.Anaerobic bacteria are explained as being “unable to grow in presence of O2”. We have been firmly under the impression that anaerobic bacteria are living organisms that have the positive volition of “not growing in the presence of O2”, based on the researches on the oxygen adaptation mechanism of anaerobic bacteria. This review article introduces the growth behaviors of bacteria classified as obligatory to facultative anaerobic bacteria, such as Clostridium, Bifidobacterium, or lactic acid bacteria, under various O2 concentrations. Further, their growth aspects in nature are assessed based on our analysis results.
