Engineering a Photoautotrophic\nMicrobial Coculture\ntoward Enhanced Biohydrogen Production

The application of synthetic phototrophic microbial consortia\nholds\npromise for sustainable bioenergy production. Nevertheless, strategies\nfor the efficient construction and regulation of such consortia remain\nchallenging. Applying tools of genetic engineering, this study successfully\nconstructed a synthetic community of phototrophs using Rhodopseudomonas palustris (R. palustris) and an engineered strain of <i>Synechocystis sp</i> PCC6803\nfor acetate production (<i>Synechocystis_acs</i>), enabling\nthe production of biohydrogen and fatty acids during nitrogen and\ncarbon dioxide fixation. Elemental balance confirmed carbon capture\nand nitrogen fixation into the consortium. The strategy of circadian\nillumination effectively limited oxygen levels in the system, ensuring\nthe activity of the nitrogenase in R. palustris, despite oxygenic photosynthesis happening in <i>Synechocystis</i>. When infrared light was introduced into the circadian illumination,\nthe production of H<sub>2</sub> (9.70 μmol mg<sup>–1</sup>) and fatty acids (especially C16 and C18) was significantly enhanced.\nProteomic analysis indicated acetate exchange and light-dependent\nregulation of metabolic activities. Infrared illumination significantly\nstimulated the expression of proteins coding for nitrogen fixation,\ncarbohydrate metabolism, and transporters in R. palustris, while constant white light led to the most upregulation of photosynthesis-related\nproteins in <i>Synechocystis_acs</i>. This study demonstrated\nthe successful construction and light regulation of a phototrophic\ncommunity, enabling H<sub>2</sub> and fatty acid production through\ncarbon and nitrogen fixation.