Annual progress Report on research related to our research project “Stabilization of Plutonium in Subsurface Environments via Microbial Reduction and Biofilm Formation” funded by the Environmental Remediation Sciences Division (ERSD) Page: 2 of 7
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Pu(VI) and Pu(V) are soluble at neutral pH but in
the presence of chelators and bacterial cells these
species tend to reduce rapidly to Pu(IV). The data
in figure 1 show the changes in total aqueous
Pu(VI)/Pu(V) concentrations during the cell
suspension experiments performed to examine
Pu(VI) and Pu(V) reduction by G.
metallireducens GS15 and S. oneidensis MR1.
The experimental cultures for both G.
metallireducens GS15 and S. oneidensis MR1
with live cells and electron donor show the most
rapid decrease in soluble Pu concentrations
(Pu(V) and Pu(VI)) relative to the control cultures
(Figure 1 A and B). There were no significant
changes in soluble Pu concentrations in the
controls with no cells and with heat-killed cells.
The control with live cells and electron donor also
show a decrease of soluble Pu indicating an active
reduction process. By the end of the experiment
most of the added Pu(VI) was present as Pu(V) in
the controls without cells or with dead cells.
However the soluble Pu concentration remained
unchanged because Pu(V) is soluble. In the
experimental cultures with live cells all initial
Pu(VI) was reduced to Pu(IV).
We characterized the solids formed using
defuse reflectance and transmission electron
microscopy imaging (TEM). The defuse reflectance
spectra of colloidal Pu(IV) obtained by precipitation
of Pu(IV) at near neutral pH and bioreduction solids
obtained by incubation of 0.5 mM Pu(VI) with a
cell suspension of S. oneidensis MR1 are very
similar and strongly suggest that the reduction
product from our experiments is indeed colloidal
Pu(IV) (data not shown). The TEM images obtained
by visualization of the solids obtained from the bio-
reduction of Pu(VI) by S. oneidensis MR1 are
shown in Figure 2. We have also obtained TEM
images of U(VI) solids obtained following U(VI)
reduction by S. oneidensis MR1 for comparison
(data not shown). The images obtained for both Pu
and U show the precipitation of actinides on the cell
surface in addition to aggregates of solids dispersed
between the cells. The TEM images of an expanded
view of the Pu solids deposited near the cell surface
0 5 10 15 20 25 3~
No cells control
tes_ killed control
Active cells with electron donor'
0 5 10 15 20
Figure 1. Direct reduction of Pu(VI) by cell suspensions of
Shewanella Oneidensis MRI (A) and Geobacter
metallireducens GS15 (B). Conditions: Cell density = 5 x
108 cells/mL suspended in 100 mM MOPS at pH = 7.4,
[Pu(VI)] = 0.50 mM, T= 30 C. The concentration of the
electron donor were [Acetate] = 10 mM for S. Oneidensis
MR1(A)and [Lactate] = 10 mM for Geobacter
metallireducens GS15 (B). (A) Live cells with the electron
donor, (A) live cells with no electron donor, (0) no cells
1 i11 "
Figure 2. TEM image biogenic Pu(IV) solids obtained
by bioreduction of Pu(VI) by cell suspension of S.
Oneidensis(left) and an expanded view of cell wall area
showing the crystalline morphology of the Pu solids (right).
No cells con trol
+ 4t Heat kiffed cellscontrc:
cl~f) oor -
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New, Mary. Annual progress Report on research related to our research project “Stabilization of Plutonium in Subsurface Environments via Microbial Reduction and Biofilm Formation” funded by the Environmental Remediation Sciences Division (ERSD), report, June 1, 2006; Los Alamos, New Mexico. (digital.library.unt.edu/ark:/67531/metadc881377/m1/2/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.