Metabolism of polyhalogenated compounds by a genetically engineered bacterium

Abstract

THE decomposition of organic compounds by bacteria has been studied for almost a century¹, during which time selective enrichment culture has generated microoganisms capable of metabolizing thousands of organic compounds. But attempts to obtain pure cultures of bacteria that can metabolize highly halogenated compounds², a large and important class of pollutants^3,4, have been largely unsuccessful. Polyhalogenated compounds are most frequently metabolized by anaerobic bacteria as a result of reductive dehalogenation reactions⁵, the products of which are typically substrates for bacterial oxygenases⁶. Complete metabolism of polyhalogenated compounds therefore necessitates the sequential use of anaerobic and aerobic bacteria⁷. Here we combine seven genes encoding two multi-component oxygenases in a single strain of Pseudomonas which as a result metabolizes polyhalogenated compounds by means of sequential reductive and oxidative reactions to yield non-toxic products. Cytochrome P450_cam monooxygenase reduces polyhalogenated compounds⁸, which are bound at the camphor-binding site^9,10, under subatmospheric oxygen tensions⁹. We find that these reduction products are oxidizable substrates for toluene dioxygenase. Perhalogenated chlorofluorocarbons also act as substrates for the genetically engineered strain.