The ecophysiology of Earth’s first phototrophs: Using modern systems to unlock Earth’s past

The emergence of oxygen-evolving photosynthesis is credited with altering global biogeochemical cycles that ultimately ushered in complex life. However, anoxygenic photosynthesis likely emerged prior to oxygenic photosynthesis. The physiology and taxonomy of the first anoxygenic phototrophs remains unknown as does the ecophysiology of the earliest two-photosystem oxygenic phototrophs. These questions are confounded by the taxonomic and physiological diversity of extant phototrophs, particularly anoxygenic phototrophs, and the rarity of characterized deeply branching oxygenic phototrophs. In my lab, we examine phototrophs in environments that mimic those thought to be present on early Earth to help address these outstanding questions. Here I will discuss an emerging model cyanobacterium that performs anoxygenic photosynthesis and the taxonomic and metabolic diversity of anoxygenic photosynthesis across physicochemical space.