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: 3 of 7
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(figure 2 right) show aggregates of nanoparticules of crystalline Pu(IV) deposited on the
surface of the cells.
2.1.2 Np(V) reduction by metal reducing bacteria Geobacter metallireducens
GS15 and Shewanella oneidensis MR1. We examined the ability of metal reducing
bacteria Geobacter metallireducens GS15 and Shewanella oneidensis MR1 to reduce
neptunium(V) and neptunium(V)-citrate. The toxicity of Np(V) to these organisms was
also examined under growth conditions in a Fe(III)-citrate growth medium. Growth was
significantly inhibited (a toxic effect) with Np(V)-citrate concentrations of 4 mM and
greater for both bacteria. No inhibition
was observed when Np(V)-citrate
concentrations were 2 mM or less, and
both Fe(III) and Np(V) were rapidly
reduced. Cell suspensions of S.
oneidensis were able to directly reduce
unchelated Np(V) to insoluble
Np(IV)(s); however, cell suspensions of
G. metallireducens were unable to
reduce unchelated Np(V). The addition
of citrate as a complexing agent for
Np(V) led to an enhanced Np(V)
reduction rate by S. oneidensis and an
observable reduction rate by G.
metallireducens. However, growth was
not observed for either organism when
unchelated Np(V) or Np(V)-citrate were
T -e ,Iours;
" MR1 N~',IV,
o MR1 N p(V] heat lled
- .- MR NplVl NQ peII
" 0" MR1 NpCV NaIad~aIe
Figure 3. Direct reduction of Np(V)-citrate by a cell suspension
of S. oneidensis. Conditions: Cell density = 4 x 108 cells/nL
suspended in 100 mM MOPS, [Np(V)] = 0.50 mM, [citrate] = 50
mM, T= 30 C.
provided as the sole electron receptors. During
Np(V)-citrate reduction, the reduced form of neptunium remained soluble, presumably as
a poly-citrate complex.
2.1.3 Pu(IV)(OH)4(am) reduction by metal reducing bacteria Geobacter
metallireducens GS15 and Shewanella oneidensis MR1. We examined the ability of
these metal reducing bacteria to reduce freshly precipitated Pu(IV)(OH)4(am) under cell
suspension conditions and examined the effect of chelating ligands on this process. Cell
suspensions of metal reducing bacteria were found to reduce minimal amounts of
Pu(IV)(OH)4(am). Shewanella oneidensis MR1 is slightly more efficient and reduces
about 8 % of total plutonium added compared to less than 1 % for Geobacter
metallireducens GS 15. In the presence of one equivalent of EDTA both Shewanella
oneidensis MR1 and Geobacter metallireducens GS15 completely reduced and dissolved
Pu(IV)(OH)4(am). The concentration of Pu(III) in the cultures was followed by UV-
visible spectroscopy and by scintillation counting of the amounts of soluble Pu. The data
in figures 3 A and B show the evolution of Pu(III) concentration over time determined
spectrophotometrically. In order to understand the mechanism by which complexants like
EDTA enhance bacterial ability to reduce and solubilize Pu hydrous oxides, we
investigated the reduction of soluble Pu(IV)(EDTA) by cell suspensions of these bacteria.
We found that the apparent rate of Pu(IV)(EDTA) reduction (~ hours) is significantly
faster than the apparent rates observed with other actinides (~ days). Both bacteria
examined here were unable to use any of the plutonium forms tested as an electron
acceptor to support their growth.
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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/m1/3/: accessed October 15, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.