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.