(703d) Investigation of Shewanella Oneidensis MR-1 and Community 31 for Microbial Reduction of Iodate at the Hanford Site

Radioiodine-129 (I¹²⁹) from leaking nuclear waste storage tanks is one of the major contaminants of groundwater at the Hanford Site in Washington State. Speciation of I¹²⁹ in the contaminated groundwater is predominantly as iodate, organo-iodide and iodide. A forthcoming bioremediation solution is to use microbial dissimilatory reduction of iodate to iodide. Shewanella oneidensis MR-1, a strain of bacteria known to reduce silver, lead and uranium, was investigated in this study for its potential to serve as a bioremediation agent against iodate contaminants. For this purpose, MR1 was grown in minimal media in the presence of iodate under both aerobic and anaerobic conditions for 24 hours. During each experiment, the amount of iodate present in the growth medium was monitored by colorimetric assays with UV Spectrophotometry. Data suggest that, within 24 hours, MR-1 could reduce iodate content in the medium by 33.8% in aerobic conditions, whereas no reduction was observed in anaerobic conditions. Additionally, iodate reduction experiments using a community of bacteria collected from groundwater at the Hanford Site, named Community 31, suggest that there may be local bacteria capable of reducing iodate. Similar experiments as those carried out with MR-1 were conducted using Community 31. The results showed that the community may be capable of reducing iodate by 45.8% in aerobic conditions. No reduction was observed in anaerobic conditions.

Future work would explore MR-1’s reduction capabilities in concert with Community 31 in suspension as well as in biofilm cultures. Findings from these experiments could lead to the development of novel methods for in situ bioremediation of iodate and to the design of novel bioreactors for the bioremediation of soils and sediments.