Metabolic Functions of Anoxygenic Photosynthetic Bacteria and Their Applications in Environmental Engineering
Anoxygenic photosynthetic bacteria (APB) are a phylogenetically diverse group of prokaryotes that perform photosynthesis without oxygen evolution. They possess versatile metabolic capabilities, including anaerobic photophosphorylation, carbon fixation, multi-substrate metabolism, and metal oxidation-reduction, enabling them to thrive in diverse environments such as lakes, rivers, soils, salt lakes, and hot springs. APB play a pivotal role in biogeochemical cycling of carbon, nitrogen, sulfur, and metals. This review systematically summarizes the metabolic diversity of APB, emphasizing their ability to utilize organic and inorganic compounds as electron donors and carbon sources. We highlight recent advances in understanding extracellular electron transfer (EET) mediated by exogenous electron shuttles and conductive materials, which expand the electron sources available for energy generation and reducing power. In environmental engineering, APB show promise in carbon sequestration, pollutant degradation (including azo dyes and heavy metals), biohydrogen production, and microbial fuel cells. For instance, Rhodopseudomonas palustris can fix CO2 under dark anoxic conditions via syntrophic interspecies electron transfer, achieving enhanced carbon fixation. Additionally, APB-based biohybrid systems incorporating CdS nanoparticles demonstrate light-driven degradation of azo dyes without external electron donors. Challenges remain in scaling up these technologies, optimizing reactor conditions, and understanding metabolic regulation. Future research should focus on genetic engineering to enhance APB performance and integrating APB into circular bioeconomy frameworks.