Enzymatic Differences Between Aerobes and Anaerobes
Aerobes require oxygen because they have metabolic pathways that utilize oxygen to convert the energy of primary substrates into the readily available form of ATP. Anaerobes have other pathways that may result in similar end products, but they don’t require molecular oxygen for their realization.
On the routes of cellular metabolism oxygen can be transformed into a number of forms that are highly biochemically active and therefore toxic, mainly hydrogen peroxide and superoxide. Cells that survive in the presence of oxygen contain enzymes converting oxygen metabolites into non-toxic forms. For instance, aerobic bacteria contain the enzyme catalase, which breaks down hydrogen peroxide, and superoxide dismutase, which neutralizes superoxide anion. Strict anaerobes usually don’t possess these enzymes. As an exception, some of strict anaerobes may carry certain amounts of superoxide dismutase or catalase.
Aerobes have got the adaptation to live at a higher redox potential of the medium, anaerobes – at a lower one. It is worthy to note that anaerobic bacteria are not passive bystanders on the growth – they are capable of active decreasing of the medium redox potential after intensive metabolic reactions. Thus, anaerobes demonstrate the marked capacity to re-organize the microsurroundings for their own needs.