Poster Presentation 2-31

The Biological Water-Gas Shift Reaction in the

Photosynthetic Bacterium Rubrivivax gelatinosus

Pin-Ching Maness*, Gary Vanzin, Jie Huang, Vekalet Tek, Sharon Smolinski

National Renewable Energy Laboratory

1617 Cole Blvd., Golden, Colorado 80401 USA

Phone: 303-384-6114; Fax: 303-384-6150; E-mail: HYPERLINK "mailto:pinching_maness@nrel.gov" pinching_maness@nrel.gov

Upon feeding CO to the culture gas phase, the purple non-sulfur photosynthetic bacterium Rubrivivax gelatinosus exhibits a water-gas shift (CO shift) reaction according to the equation: CO + H2O ↔ H2 + CO2. Carbon monoxide was demonstrated to induce the proteins necessary for the overall shift reaction. At least 10% CO is required during culturing to ensure maximal induction. Although a phototroph, once induced, this bacterium carries out the CO shift reaction equally well both in light and in darkness. At ambient temperature, the equilibrium of the reaction favors the direction of H2 production. Consequently, biological CO shift reaction is an ideal process to produce additional H2 from synthesis gas, and the latter can be produced from the gasification of waste biomass. Bacterial CO shift pathway involves a series of intricate enzymatic reactions, initiated by the enzyme CO dehydrogenase (CODH) catalyzing the CO oxidation step, and the reducing equivalents from which are then transferred, via a ferredoxin-like iron-sulfur protein, to a terminal hydrogenase yielding H2. Our effort in biochemistry has resulted in the partial purification of the CODH enzyme. Our effort in molecular biology has led to the identification of the partial sequences of seven putative genes involved in CO shift, three of which encode CODH, ferredoxin and the hydrogenase. Their amino acid sequences show high level of homology with those from Rhodospirillum rubrum. More work is underway to decipher genes in the flanking region and to predict their function with the intent to genetically engineer microbes to produce more H2, constitutively.