Organotrophy

Organotrophy is a metabolic strategy in which organisms obtain electrons for energy metabolism from organic compounds. This is in contrast to lithotrophy, where electrons are derived from inorganic substrates such as hydrogen, ammonia, or ferrous iron. Organotrophy is a form of chemotrophy, since redox energy is generated through chemical reactions, and it can be expressed in several lifestyle variants depending on how the organism harvests energy.

In organotrophic metabolism, common electron donors are organic molecules such as sugars, alcohols, organic acids, amino acids, and aromatic compounds. The electrons from these donors are transferred to an electron acceptor, which may be oxygen (aerobic respiration), nitrate, sulfate, ferric iron, or other inorganic or organic acceptors. If no external electron acceptor is available, the organism may survive by fermentation, disposing of electrons through the reduction of organic compounds or other internal pathways.

Most organotrophs are heterotrophs, using organic carbon sources for growth. However, the distinction between electron donor and carbon source means that some organisms can be organotrophic while fixing carbon dioxide, or can combine organotrophy with phototrophic energy capture in photoorganotrophic modes.

Organotrophy is ecologically widespread and underpins the degradation of organic matter in soils, sediments, and animals’ guts. It plays a central role in biogeochemical cycles, wastewater treatment, and various industrial processes, and it provides a framework for understanding microbial energy flow and nutrient turnover in diverse environments.