Plasmids in the Biodegradation of Chlorinated Aromatic Compounds
Over the past several decades, man-made chlorinated aromatic compounds have been released into the environment in massive amounts in the form of herbicides, pesticides, refrigerants, lubricants or simply as industrial or hygienic household products. The presence of chlorine atoms on such molecules renders them toxic for microorganisms, insects and pests, and in some cases for human beings. The effectiveness of such compounds as insecticides or bacteriocidal agents prompted the chemical industry to manufacture varied types of the compounds and use them for enhanced agricultural productivity, various industrial processes and as health and beauty aids. The number of naturally-occurring compounds having carbon-chlorine bonds is very limited, so that microorganisms in nature have a limited capability to act upon all the complex chlorinated compounds synthesized by man. This has resulted in the persistence of these compounds and because such compounds have been widely disseminated in nature, they have created enormous problems of toxic chemical pollution, as exemplified by the episodes in the Love Canal area, the pollution in the James River or the accidental release of extremely toxic dioxins in Seveso, Italy2. Although over the years, microorganisms have been reported to slowly biodegrade various chlorinated compounds by co-oxidative metabolism3, there is still no evidence that pure cultures have acquired the ability to biodegrade highly chlorinated compounds. Reports of pure cultures capable of degrading simple mono- or dichloro compounds are now becoming available4,5. The purpose of this short article is to review the genetic basis of the biodegradation of simple chlorinated aromatic compounds such as 4-chlorobiphenyl (pCB) or 3-, 4- or 3,5-dichloro-benzoic acids by pure cultures, and examine the roleof Plasmids in extending the range of chlorinated substrates that can be consumed by various bacterial genera.
KeywordsDegradative Pathway Meta Pathway Toxic Dioxin Plasmid Substrate Antibiotic Resistance Plasmid
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