Examples of halogenated compounds
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(Kirk-Othmer Encyclopedia of Chemical Technology
Published by John Wiley & Sons, Inc.)
Biodegredation of halogenated compounds depends on the ability of bacterial dehalogenase enzymes to catalyze the cleavage of the carbon-chlorine bonds. There are seven known mechanisms for enzyme-catalyzed dehalogenation: reductive, oxygenolytic, hydrolytic, and thiolytic dehalogenation; intramolecular nucleophilic displacement; dehydrohalogenation; and hydration. (Fetzner, 1998 reviews the chemistry involved in these processes). Reductive dehalogenation in methanogenic conditions, as well as aerobic degradation with monooxidase of persistent compounds such as DDT and polychlorinated biphenyls has been observed.
PCP is degraded both aerobically by bacteria with monooxygenase enzyme, and anaerobically through the process of reductive dechlorination. Anaerobic degradation relies on methanogenic or sulfidogenic microbial consortia in the presence of additional carbon source. These microorganisms derive energy from the halogenated compounds (in contrast to the haloalkyl degraders which simply cometabolize contaminants) and are very substrate specific in the types of chemicals they can degrade. (Atlas and Bartha, 1998).