PNNL

Abstract

Microbial phototrophs are key primary producers on Earth. Currently known electron donors for microbial photosynthesis include H2O, H2, H2S and other reduced inorganic compounds. We describe a new form of metabolism linking anoxygenic photosynthesis to anaerobic respiration, or “syntrophic anoxygenic photosynthesis.” We show that photoautotrophy in green sulfur bacterium Prosthecochloris aestaurii can be driven not only by electrons from a graphite electrode, but also by acetate oxidation via interspecies electron transfer from heterotrophic partner bacterium Geobacter sulfurreducens. P. aestuarii photosynthetic growth using reductant provided by either an electrode or syntrophy was robust and light-dependent. By contrast, P. aestuarii did not grow in co-culture with a G. sulfurreducens mutant lacking a trans-outer membrane porin-cytochrome protein complex required for direct intercellular electron transfer,. This syntrophic interaction suggests revisitation of global carbon cycling in anoxic environments and lays a foundation for further engineering of phototrophic microbial communities for biotechnological applications, such as waste treatment and bioenergy production.