The use of HRTEM techniques and the NanoSIMS to chemically and isotopically characterize Geobacter sulfurreducens surfaces

The ion-imaging capabilities of nanoscale secondary-ion mass spectrometry (NanoSIMS) and advanced high-resolution TEM have been combined in order to characterize the surfaces of Geobacter sulfurreducens and the bioprecipitated uranium phases. The results reveal an association between nutrient uptake and precipitation of U minerals. Biosequestration of U is enhanced by the addition of nutrients such as acetic acid; U is precipitated on the surface of the bacteria as nanocrystals of uraninite. The bioprecipitation of this anhydrous U-rich phase is significant; although UO (sub 2) is thermodynamically stable over a range of pH values (2-12) and oxidizing conditions [E (sub H) 0.2 to -0.2, or log f(O (sub 2) ) of approximately -50 to -125], thermodynamic models of inorganic systems suggest that U (super 6+ ) oxyhydroxide minerals should be stable. The results suggest that the biofilm shielded the UO (sub 2) from re-oxidation and that bacteria can immobilize uranium for extended periods, even under relatively oxidizing conditions in the subsurface.