Microbial genes and enzymes in the degradation of chlorinated compounds

Microorganisms are well known for degrading numerous natural compounds. The synthesis of a multitude of chlorinated compounds by the chemical industry and their release into the natural environment have created major pollution problems. Part of the cause of such pollution is the inability of natural microorganisms to efficiently degrade synthetic chlorinated compounds. Microorganisms are, however, highly adaptable to changes in the environment and have consequently evolved the genes that specify the degradation of chlorinated compounds to varying degrees. Highly selective laboratory techniques have also enabled the isolation of microbial strains capable of utilizing normally recalcitrant highly chlorinated compounds as their sole source of carbon and energy. The evolution and role of microbial genes and enzymes, as well as their mode of regulation and genetic interrelationships, have therefore been the subjects of intense study. This review emphasizes the genetic organization and the regulation of gene expression, as well as evolutionary considerations, regarding the microbial degradation of chlorobenzoates, chlorocatechols, and chlorophenoxyacetic acids.