Fermentation is very useful to many microorganisms because it allows them to generate ATP in the absence of oxygen or other external electron acceptors. Fermentation is an anaerobic process that converts organic compounds such as glucose into simpler compounds, such as ethanol, lactate, or acetate, while regenerating the oxidized electron carriers NAD+ or NADP+. This process is essential for many microorganisms that live in environments where oxygen is limited or absent, such as the gastrointestinal tracts of animals, anaerobic sediments, and acidic soils.
The terminal electron acceptors of fermentation are organic compounds, such as pyruvate or acetaldehyde, which are reduced by the oxidized electron carriers NADH or NADPH, regenerating NAD+ or NADP+ and producing the fermentation end products. Unlike in aerobic or anaerobic respiration, where oxygen or other external electron acceptors are used as the terminal electron acceptor, fermentation relies on organic compounds within the cell as the terminal electron acceptor. As a result, fermentation produces much less ATP than aerobic or anaerobic respiration.
The type of fermentation and the fermentation end products produced by microorganisms vary depending on the organism and the environmental conditions. For example, lactic acid fermentation is used by some bacteria and fungi to convert glucose into lactic acid, while alcoholic fermentation is used by yeasts and some bacteria to produce ethanol and carbon dioxide.
In summary, fermentation is a useful process for many microorganisms because it allows them to generate ATP in the absence of external electron acceptors, such as oxygen. The terminal electron acceptors in fermentation are organic compounds within the cell, which are reduced by the oxidized electron carriers NADH or NADPH, regenerating NAD+ or NADP+. Fermentation produces much less ATP than aerobic or anaerobic respiration and can result in a variety of fermentation end products depending on the organism and the environmental conditions.