Coping with a Halogenated One-Carbon Diet: Aerobic Dichloromethane-Mineralising Bacteria

Abstract

The degradation by bacteria of man-made, often toxic halogenated chemicals present as contaminants in the environment is a subject that continues to fascinate scientists and the general public alike. This interest has stimulated research on the organisms capable of mineralising halogenated pollutants, and on the enzymes and genes involved in this metabolism. In the case of dichloromethane-mineralising aerobic bacteria, which are the subject of this review, dehalogenative metabolism is stripped down to its bare essentials: a single enzyme, dichloromethane dehalogenase, consisting of a single polypeptide, catalyses the cleavage of two carbon-halogen bonds from a single carbon atom, and allows growth of the bacterial host with dichloromethane as the sole carbon and energy source. The attractive simplicity of this system has made the mineralisation of dichloromethane by aerobic bacteria a well-studied and important paradigm for dehalogenative metabolism. However, recent evidence suggests that genes and proteins other than dichloromethane dehalogenase are also specifically required, and sometimes even essential, for growth of aerobic bacteria with dichloromethane. The characterisation of such accessory genes and proteins is a promising area of enquiry for the postgenomic age of bacterial biodegradation research.