Single Phototrophic Bacterium-Mediated Iron Cycling in Aquatic Environments.

Redox cycling of iron plays a pivotal role in both nutrient acquisition by living organisms and the geochemical cycling of elements in aquatic environments. In nature, iron cycling is mediated by microbial Fe(II)-oxidizers and Fe(III)-reducers or through the interplay of biotic and abiotic iron transformation processes. Here, we unveil a specific iron cycling process driven by one single phototrophic species, SW2. It exhibits the capability to reduce Fe(III) during bacterial cultivation. A -type cytochrome is identified with Fe(III)-reducing activity, implying the linkage of Fe(III) reduction with the electron transport system. SW2 can mediate iron redox transformation, depending on the availability of light and/or organic substrates. Iron cycling driven by anoxygenic photoferrotrophs is proposed to exist worldwide in modern and ancient environments. Our work not only enriches the theoretical basis of iron cycling in nature but also implies multiple roles of anoxygenic photoferrotrophs in iron transformation processes.