Siderophores Reshape Microbial Fe(III) Reduction and Arsenic Release From Iron (Oxyhydr)Oxides

Abstract

High‐arsenic (As) groundwater is a global environmental concern, with As release largely governed by microbial reductive dissolution of Fe(III) (oxyhydr)oxides. Dissolved organic matter (DOM) rich in Fe‐complexing ligands can modify these reactions, yet its influence on Fe(III) (oxyhydr)oxides transformation and associated As mobility remains poorly constrained. Here, we investigated the microbial reduction of As‐bearing goethite by Shewanella oneidensis MR‐1 in the presence of the hydroxamate siderophore desferrioxamine B (DFOB), used as a model strong Fe‐complexing organic ligand, Luria–Bertani rather than a compositional analogue of bulk DOM. Results showed that DFOB markedly enhanced microbial Fe(III) reduction, increasing initial reduction rates by up to 70% and total Fe(II) production by 24% relative to MR‐1‐only controls. This acceleration stemmed from DFOB‐facilitated Fe(III) complexation and improved electron‐transfer interactions between MR‐1 and goethite. Arsenic release occurred in all treatments and was positively correlated with the amount of reacted Fe (dissolved plus reduced Fe), indicating coupled Fe‐As redox cycling. Despite stimulating Fe(III) reduction, DFOB did not promote additional As release, with MR‐1‐DFOB treatments exhibiting As mobilization similar to MR‐1‐only controls. This constrained As release was likely associated with DFOB‐mediated redistribution of biogenic Fe(II) into solid‐associated Fe pools and secondary Fe‐rich phases, including locally observed nano‐magnetite, minor siderite, and possibly poorly crystalline Fe phases, which may have contributed to As retention through adsorption and coprecipitation. These results reveal that DOM rich in Fe‐complexing ligands, such as siderophores, can promote the formation of As‐sequestering Fe‐mineral phases, uncovering an unrecognized control on Fe‐As interactions that may shape groundwater As mobilization.