Metabolism of polyhalogenated compounds by a genetically engineered bacterium

Abstract

The decomposition of organic compounds by bacteria has been studied for almost a century, during which time selective enrichment culture has generated microorganisms capable of metabolizing thousands of organic compounds. But attempts to obtain pure cultures of bacteria that can metabolize highly halogenated compounds, a large and important class of pollutants, have been largely unsuccessful. Polyhalogenated compounds are most frequently metabolized by anaerobic bacteria as a result of reductive dehalogenation reactions, the products of which are typically substrates for bacterial oxygenases. Complete metabolism of polyhalogenated compounds therefore necessitates the sequential use of anaerobic and aerobic bacteria. 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 P450cam monooxygenase reduces polyhalogenated compounds, which are bound at the camphor-binding site, under subatmospheric oxygen tensions. We find that these reduction products are oxidizable substrates for toluene dioxygenase. Perhalogenated chlorofluorocarbons also act as substrates for the genetically engineered strain.