Biooxidation and Bioreduction

The main forms of biologically available and convertible forms of energy in microbial cells are reduced NAD(P), ATP, and the proton-motive force (the gradient of protons across cellular membranes). Oxidation–reduction is the loss–gain of electrons followed by the transformation of protons. Energy is released in a cell from an electron donor (energy source) in coupled oxidation–reduction reactions. Fermentation is an intramolecular oxidation–reduction reaction. There is no external acceptor of electrons in fermentation. Respiration is the oxidation of chemical substances by an electron acceptor. Anaerobic respiration is oxidation of substances with terminal acceptors of electrons such as NO₃ ^-, Fe³⁺, SO₄ ^2-, and CO₂. Aerobic respiration is the oxidation of the substances with oxygen as the terminal electron acceptor. The result of respiration is a proton-motive force. The controlled passage of protons back across the membrane through specific membrane proteins is used to drive ion transport, cell motility, or ATP synthesis. The integrity of the cell membranes, where a proton-motive force is created and ATP is synthesized, is very important for the microbial cell viability. Organic solvents, heavy metals, and oxidants can easily destroy the integrity of the cell membrane and the production of energy in the cell. A tutorial with solutions and a quiz bank are added to this chapter.