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The application of HRTEM techniques and NanoSIMS
to chemically and isotopically characterize Geobacter
Sulfurreducens surfaces
Fayek M., Utsunomiya S., Pfiffner S. M., White D.
C., Riciputi L. R., Ewing R. C., Anovitz L. M., and
Stadermann F. J. (2005) Canadian Mineralogist 43,
1631-1641.
ABSTRACT
Bioprecipitated minerals are typically at the nanometer
scale, hydrous, and beam-sensitive (i.e., can
recrystallize during analysis), making them difficult to
characterize using standard spectroscopic or electron-beam
techniques. We have combined the ion-imaging capabilities of
nanoscale secondary-ion mass spectrometry (NanoSIMS) and
advanced high-resolution transmission electron microscopy
(HRTEM) in order to characterize the surfaces of
Geobacter sulfurreducens and the bioprecipitated
uranium phases. Our results reveal the association between
nutrient uptake and precipitation of uranium minerals.
Biosequestration of uranium is enhanced by addition of
nutrients such as acetic acid, and uranium is precipitated
on the surface of the bacteria as nanocrystals of uraninite
(UO2). The bioprecipitation of this anhydrous
U-rich phase is significant; although UO2 is
thermodynamically stable over a range of pH values (2 to 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. Our
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.
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