Nitrate and radioiodine (I-129) contamination is widespread in groundwater underneath the Central Plateau of the Hanford Site. I-129 a byproduct of nuclear fission, is of concern due to a 15.7 million year half-life, and toxicity. The Hanford 200 West Area contains plumes covering 4.3 km(2) with average I-129 concentrations of 3.5 pCi/L. Iodate accounts for 70.6% of the iodine present and organo-iodine and iodide make up 25.8% and 3.6%, respectively. Nitrate plumes encompassing the I-129 plumes have a surface area of 16 km(2) averaging 130 mg/L. A nitrate and iodate reducing bacterium closely related to Agrobacterium, strain DVZ35, was isolated from sediment incubated in a I-129 plume. Iodate removal efficiency was 36.3% in transition cultures, and 47.8% in anaerobic cultures. Nitrate (10 mM) was also reduced in the microcosm. When nitrate was spliced into the microcosms, iodate removal efficiency was 84.0% and 69.2% in transition and anaerobic cultures, respectively. Iodate reduction was lacking when nitrate was absent from the growth medium. These data indicate there is simultaneous reduction of nitrate and iodate by DVZ35, and iodate is reduced to iodide. Results provide the scientific basis for combined nitrogen and iodine cycling throughout the Hanford Site.