Enzymes and operons mediating xenobiotic degradation in bacteria

Aromatic hydrocarbons constitute a major group of environmental pollutants. Bioremediation appears to be the only viable alternative for large-scale decontamination. A number of bacteria have been identified that can degrade a variety of xenobiotics. Extensive studies of the enzymes and genes involved in degradation of aromatic hydrocarbons have revealed that the degradative enzymes could be broadly grouped into two major categories, peripheral and ring-cleavage enzymes. The peripheral enzymes are the ones that catabolize the pollutants initially to a metabolite that is further degraded. A majority of peripheral enzymes are oxygenases that hydroxylate the aromatic compounds, rendering them susceptible to the enzymes of ring-cleavage pathway. The genes of ring-cleavage enzymes have been shown to be highly conserved between different bacterial species. Presently, a number of constraints limit the use of available strains for efficient bioremediation. This review describes the enzymes and genes involved in xenobiotic degradation and underscores the importance of understanding the expression and regulation of genes encoding peripheral enzymes and their intelligent manipulation using recombinant DNA technology for efficient degradation of aromatic compounds.