Extracellular Electron Transfer in Photoautotrophs and their Role in Electrogenic Activity

Abstract: Anoxygenic phototrophic bacteria are a diverse group of microorganisms, including genera such as Chloroflexus, Rubrivivax, and Rhodopseudomonas. These photoautotrophs are defined by their ability to grow using light with distinctive metabolic properties that enable them to carry out Extracellular Electron Transfer (EET) without producing oxygen as a by-product. These microorganisms play a significant role in biogeochemical cycles such as the carbon and sulfur cycles in aquatic and sedimentary environments. Their specialized photosynthetic systems, which include bacteriochlorophyll- based light-harvesting complexes and electron transport chains, allow efficient utilization of light energy under anaerobic conditions. In recent years, the application of anoxygenic phototrophic bacteria in bioelectrochemical systems has gained increasing attention. Anoxygenic phototrophs are promising candidates for technologies like microbial fuel cells and biophotovoltaic systems due to their electrogenic potential. These systems rely on microbial metabolism to convert chemical or light energy into electrical energy, while also being useful in bioremediation and wastewater treatment. Understanding the molecular basis of EET and its incorporation with photosynthetic metabolism is critical for developing bioelectrochemical technologies and expanding their environmental applications. The mechanisms of EET and their ability to obtain electrons from organic molecules or reduced compounds and transfer them to external acceptors such as iron, sulfur, or other oxidized compounds will be explored in this review. The integration of photosynthetic processes with EET and their applications in bioelectrochemical systems are critically discussed.