Nitrate-dependent iron oxidation for bioremediation of metal, metalloid, and radionuclide contaminants

Abstract

Nitrogen and iron cycling are key drivers of biogeochemical processes, particularly in anoxic environments where they can influence contaminant mobility and bioavailability. Nitrate-dependent iron oxidation (NDFO) is a microbially-mediated process in which nitrate reduction is coupled to Fe(II) oxidation, forming solid Fe(III) minerals. This metabolism, detected in diverse environments such as sediments and aquifers, can proceed autotrophically, mixotrophically, or heterotrophically. NDFO represents a potential in situ bioremediation strategy due to the widespread environmental presence of capable microbial communities and the capacity of resulting iron oxides to adsorb and immobilize contaminants. These iron minerals can incorporate or reduce various metals, metalloids, and radionuclides, including arsenic, nickel, copper, and uranium, which may also accumulate in microbial biomass. NDFO-capable microorganisms may also transform some contaminants to less mobile oxidation states. Elevated nitrate and iron concentrations at contaminated sites, such as mines, offer conditions for NDFO induction. This review examines the microbial physiology and ecology underlying NDFO, the mineralogy and contaminant-binding properties of its iron oxide products, and current research into its application for environmental remediation. Key knowledge gaps and future research directions are highlighted to support further understanding of NDFO organisms, impacts on mineral phases, and development of NDFO-based strategies for contaminant management.