What most affects the oxidation-reduction potential (Eh or redox potential) of media for anaerobic bacteria?

The oxidation-reduction potential (Eh or redox potential) of a medium is significantly influenced by the pH level because pH affects the availability of hydrogen ions (H+) in the solution, which are crucial for redox reactions. A lower pH (more acidic conditions) generally means a higher concentration of H+ ions, which can facilitate the reduction reactions that anaerobic bacteria rely on. Conversely, higher pH levels (more alkaline conditions) can limit these reactions by reducing H+ availability, negatively impacting the redox potential.

While other factors like oxygen levels, nitrogen availability, or organic substrates such as glucose also play significant roles in the overall metabolic processes of anaerobic bacteria, they do not primarily dictate the oxidation-reduction potential of the media. For instance, oxygen directly affects aerobic bacteria and would generally inhibit anaerobic processes rather than influencing the Eh in anaerobic conditions. Similarly, nitrogen is important for growth but does not directly impact redox potential in the same way that pH does. Glucose serves as an energy source rather than directly shaping the redox conditions. Therefore, pH has a more direct and profound influence on the redox potential crucial for the enzymatic activities and energy production of anaerobic bacteria.