Biochemistry of the Anaerobic Dehalogenation of Chlorinated Aromatics

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This study looks at a genus of microbes, Desulfitobacteria, that can detoxify halogenated organic pollutants such as polychlorinated biphenyls (PCBs). PCBs are listed as a "dirty dozen" persistent organic pollutant (POP) that, although banned, remain in the environment and cause lasting damage to animal health and the environment. The long-term goal is to help achieve the aim of a 2001 United Nations treaty to phase out and eventually eliminate these POPs. Thus a better understanding of how to accelerate the natural biodegradation of such compounds would be of significant value to society. Through a process known as dehalorespiration, these microbes biodegrade halogenated compounds while gaining metabolic energy. When Desulfitobacteria sense the presence of a halogenated compound, they produce a host of proteins that enable them to remove the chlorine substituent, which is the first step in its detoxification. A manifold of techniques are used to study dehalorespiration, including enzymology, molecular biology and genetics, spectroscopy, and electrochemistry. The first objective of this project is to elucidate the catalytic mechanism of the dehalogenase enzyme, which removes the chlorine substituent. To achieve this aim, each of the steps in the dehalogenase catalytic cycle will be elucidated and the role of the metal cofactors (vitamin B12 and the iron-sulfur clusters) will be determined. The second objective is to study the transcriptional regulatory protein (CprK) that controls when and how much of the dehalorespiration proteins are produced. When CprK binds dilute solutions of the halogenated compound, it attaches to a specific DNA regulatory sequence and accelerates the rate of production of the components of the dehalorespiration system. Interactions between the transcriptional regulatory protein (CprK) and the xenobiotic and between CprK and the DNA sequence will be studied. This project also includes plans to promoting teaching, training and learning; to enhance the University of Nebraska research infrastructure; and to broadly disseminate the research results.