ENGINEERING A RECOMBINANT DEINOCOCCUS RADIODURANS FOR ORGANOPOLLUTANTDEGRADATION IN RADIOACTIVE MIXED WASTE ENVIRONMENTS

Thousands of waste sites around the world contain mixtures of toxic ch lorinated solvents, hydrocarbon solvents, and radionuclides. Because o f the inherent danger and expense of cleaning up such wastes by physic ochemical methods, other methods are being pursued for cleanup of thos e sites. One alternative is to engineer radiation-resistant microbes t hat degrade or transform such wastes to less hazardous mixtures. We de scribe the construction and characterization of recombinant Deinococcu s radiodurans, the most radiation-resistant organism known, expressing toluene dioxygenase (TDO). Cloning of the tod genes (which encode the multicomponent TDO) into the chromosome of this bacterium imparted to the strain the ability to oxidize toluene, chlorobenzene, 3,4-dichlor o-1-butene, and indole. The recombinant strain was capable of growth a nd functional synthesis of TDO in the highly irradiating environment ( 60 Gy/h) of a Cs-137 irradiator, where 5x10(8) cells/ml degraded 125 n mol/ml of chlorobenzene in 150 min. D. radiodurans strains were also t olerant to the solvent effects of toluene and trichloroethylene at lev els exceeding those of many radioactive waste sites. These data suppor t the prospective use of engineered D. radiodurans for bioremediation of mixed wastes containing both radionuclides and organic solvents.