Traditional approaches to the remediation of metals and radionuclides typically utilize dissimilatory reduction processes. However, in oxygenated environments such as the vadose zone, dissimilatory reduction can be problematic. Thus, new technologies are needed to broaden the scope of available bioremediation approaches. The goal of this study was to test the feasibility of a procedure that could immobilize contaminants, e.g., uranium, in aerobic environments by modifying soil microbes to constitutively overproduce the enzyme alkaline phosphatase. The substrate of alkaline phosphatase, organic P, is highly mobile in porous media, e.g., subsurface soils. Overproduction of alkaline phosphatase was achieved by introduction of plasmid pJH123 containing a pglA-phoA hybrid gene encoding a fusion protein. Plasmid pJH123 can be transformed into a number of subsurface pseudomonad isolates; each selected for their potential in field-scale delivery systems. In the presence of selection, plasmid pJH123 was stably maintained in the majority of the subsurface hosts tested. In addition, the plasmid conferred significantly higher levels of alkaline phosphatase enzyme activity. We hypothesize that an increase in phosphate levels due to alkaline phophatase activity may result in precipitation of uranium from solution and possibly soil. Studies are ongoing to determine the applicability of this uranium immobilization bioremediation strategy.
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