photoheterotrophic

Photoheterotrophs are organisms that obtain energy from light while requiring organic compounds as a source of carbon. In contrast to photoautotrophs, which fix CO2 into biomass, photoheterotrophs rely on organic carbon from the environment or from surrounding organisms. This combination of phototrophy and heterotrophy is common in several groups of bacteria and some archaea, often under anaerobic or low-oxygen conditions.

In these organisms, light-harvesting pigments such as bacteriochlorophylls or rhodopsins drive photosynthetic electron transport, generating ATP and reducing power. The carbon skeletons are built from organic molecules such as acetate, succinate, lactate, or sugars; these organisms can grow using light as an energy source while consuming organic substrates for carbon and, in many cases, for electrons.

Representative examples include purple non-sulfur bacteria (e.g., Rhodospirillum, Rhodobacter) and green non-sulfur bacteria (e.g., Chloroflexus). They are typically found in anaerobic or microaerophilic environments such as muddy sediments, stratified lakes, hot springs, and some wastewater systems, where light is available but oxygen may be limited.

Photoheterotrophy is one of several metabolic strategies that microbes use to exploit light, and it is distinct from chemoheterotrophy (energy from chemical reactions, carbon from organic matter) and from photoautotrophy (energy from light, carbon fixed from CO2). Its ecological role includes degradation of dissolved and particulate organic matter and interactions with other microorganisms in nutrient cycles.