ABSTRACT
Abstract Highly chlorinated aromatic compounds like chlorobenzenes, polychlorinated dibenzo-p-dioxins, dibenzofurans and biphenyls are toxic, poorly watersoluble compounds, which are persistent in the environment and tend to accumulate in food chains. They are resistant to most aerobic biodegradation processes. Under anaerobic conditions, however, they can serve as electron acceptors in a respiratory process called dehalorespiration, thereby undergoing a reductive dehalogenation. In this review we summarize the current knowledge about the reductive dechlorination of chlorobenzenes and polychlorinated dioxins. A variety of pathways of microbial reductive dechlorination of dioxins and chlorobenzenes are described suggesting the involvement of different microbes in the observed dechlorination processes. The first described anaerobic bacterium able to respire with chlorinated benzenes and dioxins belongs to the genus Dehalococcoides, forming an isolated cluster within the green non-sulfur bacteria. Therefore, this review also summarizes physiological and biochemical properties of Dehalococcoides, including the remarkable specialization to dehalorespiration as a lifestyle and the capability to use a broad spectrum of halogenated compounds as electron acceptors. Biostimulation of dehalogenating bacteria present in contaminated anaerobic habitats can be a potentially useful approach to enhance natural attenuation processes and is discussed with respect to the versatility of Dehalococcoides species.
