Bacterial Growth on Halogenated Aliphatic Hydrocarbons: Genetics and Biochemistry
نویسندگان
چکیده
Many synthetically produced halogenated aliphatic compounds are xenobiotic chemicals in the sense that they do not naturally occur on earth at biologically significant concentrations. Nevertheless, various microorganisms have been isolated that possess the capacity to grow at the expense of these compounds, and to use them as a carbon and energy source under aerobic conditions. This raises a number of interesting questions concerning the mechanisms of dehalogenation, and the evolution and distribution of dehalogenase-encoding genes. For example, to what extent were the biochemical pathways for the mineralization of such xenobiotic halogenated chemicals preexisting before their large-scale anthropogenic introduction into the environment? What adaptation events at the genetic level occurred after the release of the xenobiotics? What are the origins of enzymes that cleave carbon-halogen bonds? Did similar mechanisms evolve in different organisms, at different sites, or were genes and organisms distributed from one site to another? Over the last few decades, several classes of reactions for the dehalogenation of xenobiotic compounds have been found, and in some cases the enzymatic mechanisms have been unraveled to the atomic level by x-ray crystallographic studies. At the same time, genetic studies have revealed much about the diversity, similarities, and possible distribution mechanisms of dehalogenase genes. This review focuses on the catabolic pathways for the aerobic mineralization of halogenated aliphatics, including dehalogenation reactions and issues of adaptation and distribution, with an emphasis on events that may have occurred after introduction of these xenobiotics into the environment. Bacterial growth on halogenated compounds requires the presence of enzymes that are capable of cleaving carbon-halogen bonds. The mechanisms and diversity of some
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