photoorganoheterotroph

A photoorganoheterotroph is an organism that obtains energy from light (photo-), electrons from organic compounds (organo-), and carbon from organic sources (heterotroph). The term is part of a trophic classification that distinguishes organisms by their energy, electron, and carbon sources. Photoorganoheterotrophy contrasts with photoautotrophy (light energy and inorganic carbon fixation) and chemotrophy (chemical energy sources).

Physiology of photoorganoheterotrophs typically involves photophosphorylation driven by light-absorbing pigments such as bacteriochlorophyll. Many use cyclic electron flow and anoxygenic photosynthetic pathways, so they do not produce O2 as a byproduct. Organic molecules serve both as electron donors and as substrates for biosynthesis and growth. Some species are facultative, switching between photoorganoheterotrophic and chemoheterotrophic or photoautotrophic modes depending on environmental conditions.

Taxa that commonly display photoorganoheterotrophy include various purple non-sulfur bacteria (e.g., Rhodobacter, Rhodospirillum) and other anoxygenic phototrophs in aquatic and soil environments. These organisms occupy niches where light is available but inorganic electron donors or fixed carbon are limited, contributing to carbon cycling and the degradation of organic compounds.

In research and applied contexts, photoorganoheterotrophs are studied for their metabolic flexibility, roles in microbial ecology, and potential uses in wastewater treatment, bioremediation, and bioenergy production. The designation is descriptive of metabolic strategy rather than a strict taxonomic grouping.