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

• Published in: Canadian mineralogist Vol. 43; pp. 1631 - 1641
• Main Authors: Fayek, M, Utsunomiya, S, Pfiffner, S. M, White, D. C, Riciputi, L. R, Ewing, R. C, Anovitz, Lawrence M, Stadermann, F. J
• Format: Journal Article
• Language: English
• Published: Mineralogical Association of Canada 01-10-2005
• Subjects: actinides; bacteria; Geobacter; Geobacter sulfurreducens; geomicrobiology; high-resolution methods; ion probe data; mass spectra; metals; microorganisms; Mineralogy; oxides; spectra; surface properties; TEM data; uraninite; uranium
• ISSN: 0008-4476
• DOI: 10.2113/gscanmin.43.5.1631

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 UO2 is thermodynamically stable over a range of pH values (2-12) and oxidizing conditions [EH 0.2 to -0.2, or log f(O2) of approximately -50 to -125], thermodynamic models of inorganic systems suggest that U6+ oxyhydroxide minerals should be stable. The results suggest that the biofilm shielded the UO2 from re-oxidation and that bacteria can immobilize uranium for extended periods, even under relatively oxidizing conditions in the subsurface.