RELATIONSHIP OF MICROBIAL PROCESSES 323 



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Fig. 7 Separation of soluble plutonium complexes in microbial cultures by gel 

 permeation chromatography. 



Application of thin-layer electrophoresis (pH 6.6, pyridine— acetate buffer system; 

 cellulose support) indicated the presence (Fig. 9) of a relatively large amount of material 

 of greater negative charge than Pu— DTPA in the exocellular fraction along with 

 Pu— DTPA. The Pu— DTPA control contained a small quantity of plutonium, likely 

 hydrolysis products, that did not migrate from the origin. The plutonium ligands in the 

 intracellular fraction were either neutral in charge in this buffer system or were of a 

 molecular size too large to migrate under the conditions of electrophoresis. Similar 

 alterations of plutonium form by a single plutonium-resistant fungus exposed continu- 

 ously to plutonium during growth have also been reported (Robinson et al., 1977). 



Several phenomena may have been responsible for the observed changes in the 

 chemical form of plutonium. The organism may have synthesized compounds that either 

 bind Pu— DTPA or bind plutonium more tightly than DTPA. thereby successfully 

 competing for plutonium in the presence of DTPA. Alternatively, the organism may 



