(341a) Application of Shewanella Biofilms for the Dissimilatory Reduction of Iodate in Groundwater

Plutonium production at the U.S. Department of Energy (DOE) Hanford Site has resulted in the generation of Iodine isotopes. The release of radioactive ¹²⁹I to the subsurface due to leaking tanks and direct disposal has resulted in several plumes in the groundwater. Speciation of Radioiodine has shown that iodate comprises a major percent of iodine. Iodate, which is a +5 oxidation state of iodine is found to be the dominant species due to its thermodynamic stability. One way to reduce iodate to iodide (-1 oxidation state) is by the action of biofilms formed by dissimilatory metal-reducing bacteria such as Shewanella oneidensis MR-1, which can gain energy for growth by coupling the oxidation of various electron donors to the reduction of iodate. The polyionic nature, physical and chemical heterogeneity of biofilm matrices, combined with the reduced susceptibility of bacterial biofilms to toxicity by inorganic and organic pollutants, make them particularly suitable for bioremediation applications. This work develops a protocol for the proliferation of S. oneidensis MR-1 biofilms and investigates the potential of these biofilms to reduce iodate. Preliminary results indicate that the presence of optimal amounts of lactate (electron donor) enhances MR1 biofilm formation and seems to interact with the speciation of iodate. These studies could lead to novel approaches and techniques for the bioremediation of radioiodine at contaminated sites.