REMOVAL OF HALOGEN, NITRO, AND SULFONATE GROUPS
A wide variety of aromatic compounds are found in the environment, some naturally, others due to human pollution. For almost all such compounds, bacteria can be isolated that degrade them. Polychlorinated biphenyls (PCBs) are industrial pollutants. Other chlorinated aromatics include selective herbicides such as 2,4-D (2-4-dichlorophenoxyacetate). Many nitro and sulfonate derivatives are used in the pharmaceutical, dye, and detergent industries. The chlorine, nitro, and sulfonate groups may be removed during the dioxygenase reaction to release chloride, nitrite, or bisulfite (Fig. 13.13). Ring dioxygenases from certain bacteria will work on substituted rings, whereas chloro, nitro, or sulfonate groups inhibit others. About 10% of the organic pollution in the river Rhine is aromatic sulfonates from the German dye industry. Not surprisingly, many bacteria isolated from the Rhine possess dioxygenases that are good at knocking off sulfonate and nitro groups.
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