Functional characterization of the formate dehydrogenase orthologue and hydrogenases in organohalide respiration by Dehalococcoides mccartyi

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A major electron donor for organohalide respiration by Dehalococcoides species is hydrogen; however, little is generally known concerning other potential electron donors for organohalide respiration. Dehalococcoides strain CBDB1 cannot use formate as an electron donor yet it synthesizes a putative formate dehydrogenase (Fdh) as one of its most abundant proteins. This fact, along with others, indicates that the enzyme has a different function. One of the aims of this proposal is therefore, to determine the physiological function of this Fdh-like enzyme in organohalide respiration. We will use combined biochemical, physiological and molecular biological approaches, together with heterologous expression in E. coli, to identify the role of the Fdh-like protein in Dehalococcoides spp. The genome of Dehalococcoides strain CBDB1 also has the capacity to synthesise probably up to 5 different types of multisubunit hydrogenase; 4 of these are predicted to be [NiFe]-hydrogenases. The fifth is predicted to be a [FeFe]-hydrogenase (Hym) although it also has strong sequence similarity to complex I components. Our aim is to resolve whether strain CBDB1 via Hym evolves as well as consumes hydrogen and to determine the contribution of the individual hydrogenases to growth in response to hydrogen partial pressure and electron acceptor spectrum during organohalide respiration.