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Abstract

The epsilon-proteobacteria form a subdivision of the Proteobacteria including the genera Wolinella, Campylobacter, Helicobacter, Sulfurospirillum, Arcobacter and Dehalospirillum. The majority of these bacteria are oxidase-positive microaerophiles; indicating an electron transport chain with molecular oxygen as terminal electron acceptor. However, numerous members of the epsilon-proteobacteria also grow in the absence of oxygen. The common presence of menaquinone and fumarate reduction activity suggests anaerobic fumarate respiration which was demonstrated for the rumen bacterium Wolinella succinogenes as well as for Sulfurospirillum deleyianum, Campylobacter fetus, Campylobacter rectus and Dehalospirillum multivorans. To date, complete genome sequences of Helicobacter pylori and Campylobacter jejuni are available. These bacteria and W. succinogenes contain the genes frdC, A and B encoding highly similar heterotrimeric enzyme complexes belonging to the family of succinate:quinone oxidoreductases. The crystal structure of the W. succinogenes quinol:fumarate reductase complex (FrdCAB) was solved recently, thus providing a model of succinate:quinone oxidoreductases from epsilon-proteobacteria. Succinate:quinone oxidoreductases are being discussed as possible therapeutic targets in the treatment of several pathogenic epsilon-proteobacteria.