Enzymes and genes for microbial metabolism ofoxochlorates

Abstract: Oxochlorates can be used as electron acceptors for microbial respiration in a variety of bacterial species, and oxochlorate respiration plays a substantial role in the biotransformation of these environmental contaminants. Although oxochlorate respirers are widely spread in the environment, only few enzymes and even fewer genes, involved in the metabolism of oxochlorates have been isolated and characterised. This thesis describes the results from studies of the enzymes and genes for chlorate respiration in Ideonella dechloratans. The transformation of chlorate to chloride ion and molecular oxygen is catalysed by two enzymes in I. dechloratans, chlorate reductase and chlorite dismutase. Chlorate reductase catalyses the reduction of chlorate to chlorite. This enzyme is trimeric () and contains a molybdopterin cofactor, iron-sulphur clusters, and haem b. Chlorate reductase belongs to class II of the dimethyl sulphoxide reductase family. Chlorite dismutase is a tetrameric haem enzyme, and decomposes chlorite to chloride ion and molecular oxygen. Recently, two homologues with high identity were discovered in the databases. Expression of the I. dechloratans chlorite dismutase gene in Escherichia coli resulted in an active recombinant enzyme with native-like catalytic properties. A detailed comparison between the native and recombinant chlorite dismutases revealed the presence of a post-translational modification, possibly a covalent cross-link in the native enzyme. The genes for chlorate metabolism were found in a cluster, in which the genes for chlorate reductase and the gene for chlorite dismutase are separated by a novel insertion sequence