Chemotrophic

Chemotrophy is a mode of metabolism in which organisms obtain energy by oxidizing chemical compounds, rather than by capturing light as in phototrophy. In chemotrophy, energy-yielding redox reactions release free energy that powers cellular processes. The term describes the energy source used by an organism, not necessarily its carbon source.

Chemotrophy is commonly divided into chemolithotrophy and chemoorganotrophy. Chemolithotrophs harvest energy from inorganic electron donors, such as ammonia, nitrite, sulfide, iron, or molecular hydrogen, and many are autotrophic, fixing carbon dioxide through pathways like the Calvin cycle or reverse TCA. Chemoorganotrophs obtain energy from organic compounds, including sugars, acids, and alcohols; they are typically heterotrophs relying on organic carbon, though some chemoorganotrophs can fix inorganic carbon under certain conditions.

Examples and ecological roles of chemotrophs underscore their importance in biogeochemical cycles. Chemolithotrophs include nitrifying bacteria (for example, Nitrosomonas and Nitrobacter), sulfur-oxidizers (such as Acidithiobacillus), and hydrogen-oxidizers; methanotrophs oxidize methane and can be chemoautotrophic. Chemoorganotrophs comprise many bacteria, such as Escherichia coli and Bacillus, as well as fungi and other organisms, and they may respire with oxygen or other electron acceptors, or ferment in anaerobic environments. In ecosystems, chemotrophs drive cycles of nitrogen, sulfur, and carbon and can support life in dark or nutrient-rich environments where phototrophy is limited.

Chemotrophy is one of several strategic modes by which organisms obtain energy and often coexists with phototrophy. The study of chemotrophic metabolism informs microbiology, ecology, and biotechnology.