Biogenic manganese oxides facilitate iodide oxidation at pH ≤ 5

ABSTRACTRadioactive 129I, a byproduct of nuclear power generation, can pose risks to human health if released into the environment, where its mobility is highly dependent on speciation. Based on thermodynamic principles, 129I should exist primarily as iodide (I−) in most terrestrial environments; however, organo-129I and 129iodate are also commonly detected in contaminated soils and groundwater. To investigate the capability of biogenic manganese oxides to influence iodide speciation, 17 manganese-oxidizing bacterial strains, representing six genera, were isolated from soils of the Savannah River Site, South Carolina. The isolates produced between 2.6 and 67.1 nmole Mn oxides (ml−1 media after 25 days, pH 6.5). Results from inhibitor assays targeting extracellular enzymes and reactive oxygen species indicated that both play a role in microbe-induced Mn(II) oxidation among the strains examined. Iodide oxidation was not observed in cultures of the most active Mn-oxidizing bacteria, Chryseobacterium sp. stra...