RELATIONSHIP OF MICROBIAL PROCESSES 321 



plutonium form in the cellular and exocellular media. In addition, an experiment was 

 conducted to distinguish complexation reactions resulting from plutonium interactions 

 with metabolites arising from normal metabolic processes and plutonium interactions 

 with metabolites arising from plutonium resistance. For this distinction plutonium was 

 added at the stationary growth phase of soil microorganisms isolated from soil in the 

 absence of plutonium, and the transport and complexation were compared with microbial 

 cultures isolated from plutonium-containing soil and grown in the presence of plutonium. 

 After growth for 96 hr, the cuhures were separated into cellular and exocellular 

 fractions. The cell fraction was. in tum, homogenized into intracellular soluble and 

 cell-debris fractions. The results of studies in which plutonium was added at the 

 stationary growth phase of cultures of fungi or bacteria grown on mixed organic acids or 

 sugars are summarized in Table 5. These cultures, selected only on the basis of their 

 ability to grow on either of two carbon sources, differed to a first approximation in their 



TABLE 5 Distribution of Plutonium in Mixed Microbial Cultures* Exposed to 

 Plutonium at Stationary Growth Phase and Grown on Different Carbon Sources 



*Cultures were not replicated. Analytical precision was < ± 10% (1 a). Plutonium present in 

 cell washes before homogenization is not included. 



interactions with plutonium. In general, the majority of the plutonium was associated 

 with the exocellular fraction, but significant quantities were insoluble and associated with 

 the cell wall and membrane fractions. However, the distribution of plutonium between 

 fractions was dependent on microorganism type and carbon source. In the case of fungi, 

 the exocellular fraction of organisms grown on the organic acid carbon source contained 

 less plutonium than when mixed sugars were used as a carbon source. Tlie reverse of this 

 relationship occurred with the bacteria. 



Differences in plutonium distribution as a function of carbon source used in 

 enrichment were also found in cultures grown in the presence of plutonium throughout 

 incubation (Table 6). The fungal cultures grown on mixed organic acids exhibited larger 

 concentrations of plutonium both in the exocellular fraction and bound to the cell-debris 

 fraction; the cultures grown on mixed sugars contained a higher fraction of added 

 plutonium in the intracellular soluble fraction. In the bacterial cultures the situation was 

 somewhat different in that higher concentrations of plutonium occurred in the 

 exocellular fraction of the culture grown in organic acids; less plutonium was associated 

 with the cell-debris fraction as compared with cells grown on sugars. 



In general, the continuous presence of plutonium during growth did not have 

 pronounced effects on the distribution of plutonium in the cultures (compare Tables 5 

 and 6). Rather, the metabolic properties of the mixed cultures as determined by carbon 

 source appeared to be the major factor resulting in the observed differences. Under both 



