After growth for 96 hr, the culturee were separated into cellular and
exocellular fractiona, The cell fraction was, in turn, homogenized into
intracellular soluble and cell debris fractions.
The results of studies
in which Pu was added at the stationary growth phase of cultures of fungi
or bacteria grown on mixed organic acide or sugare are summarized in
Table 5.
These cultures, selected only on the basis of their ability to
grow on either of two C sources, differed to a first approximation, in
their interactions with Pu.
In general, the majority of Pu was associated
with the exocellular fraction, but significant quantities were insoluble
and associated with the cell wall and membrane fractions. However, the
distribution of Pu between fractiona was dependent upon microorganism type
and C-source. In the case of fungi, the exocellular fraction of organisms
grown on the organic acid C source contained less Pu than when mixed
sugate were utilized as a C source. The reverse of this relationship
occurred with the bacteria.
Differences in Pu distribution as a function of C source used in enrichment were also found in cultures grown in the presence of Pu throughout
incubation (Table 6).
The fungal cultures grown on mixed organic acids
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*arithmetic mean of 3 samples.
In preliminary (unpublished) studies by the senior authore and others,
mixed cultures of soil organisms, fsolated from soil on the basis of C
requirements and Pu resistance, were analyzed as to their ability to transport Pu into celle and to alter Pu form in the cellular and exocellular
media.
In addition an experiment was conducted to distinguish complexation
reactions resulting from Pu interactions with metabolites arising from
normal metabolic processes and Pu interactions with metabolites arising
from Pu resistance. To make thia distinction sojl microorganisms were
isolated from soil in the absence of Pu and Pu added at the stationary
growth phase of an enriched culture, and, transport and complexation were
compared to microbial cultures isolated from Pu-contsining soiland grown
in the presence of Pu.
om
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Q
Plutonium Transport to the Spores of Aspergillue niger (Beckert and Au, 1976).
There is a growing literature on organic acida and bases, capable of
complexing heavy elements, which are produced directly or by secondary
syntheses by a variety of microorganisms. These products may be expected
to be present in soils (discussed in detail in a previous section). Their
concentration and form will be dependent upon the environmental factors
influencing microbial metaboliam, such as C-source, (previous section),
and their residence time will be dependent upon subsequent chemical and
microbiological stability.
m
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Table 4.
uptake was related to pH ard expected solubility of the Pu added with Pu
in the initially soluble nitrate and citrate forme exhibiting a factor of
2 to 3 greater uptake than the dioxide (Table 4). Availability to microorganisms of the Pu in citrate and nitrate might be expected to be considerably higher than the oxide from solubility considerations at the pCi/ml
level. The relatively high microbial availability of Pu ae the oxide is
highly significant, and further studies are warranted to determine the
mechanisms of solubilization and uptake and the significance of microorganisms in recycling processes,