Reverse electron transfer involving a butyrate-induced membrane complex during syntrophic growth of Syntrophomonas wolfei

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Syntrophic growth plays an essential role in the recycling of organic matter in anaerobic environments. A distinctive feature of syntrophic metabolism is the need for reverse electron transfer due to the unfavorable thermodynamics of critical oxidation-reduction reactions. Recent genomic and proteomic studies in the obligately anaerobic model organisms Syntrophomonas wolfei and Syntrophus aciditrophicus prvided evidence for an Etf-linked hydrogenase induced during syntrophic growth on butyrate. By Blue Native electrophoresis a complex was identified that comprised an annotated FeS oxidoreductase along with the beta subunit of Etf, and two subunits of a membrane-bound, Fe-hydrogenase. It could involve a menaquinone q-cycle or ion pumps in the coupling of the unfavorable reduction of protons to hydrogen with NADH to the favorable crotonyl-CoA reduction to butyryl-CoA with NADH.This study aims at the anaerobic purification and characterization of the butyrate-induced membrane complex from S. wolfei. This includes solubilization of wild type protein, purification via several chromatographic steps, characterization of the molecular and kinetic properties. One of the major concerns is to answer the questions which mechanism drives the unfavorable hydrogen production. Therefore, combined enzyme assays including bifurcation reactions will be used. The results of this study may extend our knowledge about sophisticated mechanisms involved in the coupling of redox reactions via membrane complexes of syntrophic organisms that depend on the production of compounds such as hydrogen that serve as substrate for their syntrophic partners in an energy limited environment.