Cyanobacteria-mediated arsenic redox dynamics is regulated by phosphate in aquatic environments.

Studies of cyanobacteria in environments where arsenic (As) and phosphate (P) both occur in significant concentrations have so far only focused on the effect of P on As(V) toxicity and bioaccumulation, with little attention to the influence of P on As redox transformations. Our study revealed that As(III) oxidation by Synechocystis appeared to be more effective with increased P levels. We demonstrated that the higher As(III) percentage in the medium under P-limited conditions was due to enhanced As(V) uptake and the subsequent efflux of intracellularly reduced As(III) which in turn contributed to higher As(III) concentrations in the medium. Arsenic redox changes by Synechocystis under P-limited conditions is a dynamic cyclic process that includes the following: surface As(III) oxidation (either in the periplasm or near the outer membrane), As(V) uptake, intracellular As(V) reduction, and As(III) efflux. These observations not only expand our understanding of how P influences microbial As redox metabolisms but also provide insights into the biogeochemical coupling between As and P in As contaminated eutrophic aquatic environments and artificial wetland-paddy fields.