Enhanced U(VI) release from autunite mineral by aerobic Arthrobacter sp. in the presence of aqueous bicarbonate

The scientific efforts of Dr. Yelena Katsenovich, Dr. Leonel Lagos and Mr. Denny Carvajal (DOE Fellow Class of 2009), in an ongoing collaboration with Dr. Dawn Wellman of the Pacific Northwest National Laboratory (PNNL), have developed an original research manuscript that was published in May 2012 in the international journal Chemical Geology. This research provides a more comprehensive understanding on the effect of microorganisms on uranium release from autunite within bicarbonate-bearing subsurface environments typical for arid climate throughout the western United State and is the first to investigate microbial dissolution of autunite mineral in the aerobic conditions. The following is an abstract, which summarizes the publication.

Abstract:
The bacterial effect on U(VI) release from the autunite mineral (Ca[(UO2)(PO4)]2·3H2O) was investigated to provide a more comprehensive understanding of the important microbiological processes affecting autunite stability within subsurface bicarbonate-bearing environments. Experiments were performed in a culture of the Arthrobacter oxydans G975 strain, herein referred to as G975, a soil bacterium previously isolated from Hanford Site soil. 91 mg of autunite powder and 50 mL of phosphorous-limiting sterile media were amended with bicarbonate (ranging between 1 and 10 mM) in glass reactor bottles and inoculated with the G975 strain after the dissolution of autunite was at steady state. SEM observations indicated that G975 formed a biofilm on the autunite surface and penetrated the mineral cleavages. The mineral surface colonization by bacteria tended to increase concomitantly with bicarbonate concentrations. Additionally, a sterile cultureware with inserts was used in non-contact dissolution experiments where autunite and bacteria cells were kept separately. The data suggest that G975 bacteria is able to enhance the release of U(VI) from autunite without direct contact with the mineral. In the presence of bicarbonate, the damage to bacterial cells caused by U(VI) toxicity was reduced, yielding similar values for total organic carbon (TOC) degradation and cell density compared to U(VI)-free controls. The presence of active bacterial cells greatly enhanced the release of U(VI) from autunite in bicarbonate-amended media.

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