Upon feeding CO to the gas phase of a photosynthetic bacterium Rubrivivax gelatinosus CBS, a CO oxidation: H-2 production pathway is quickly induced. Hydrogen is produced according to the equation CO + H2O - CO2 + H-2. Two enzymes are known to be involved in this pathway: a CO dehydrogenase (CODH) with a pH optimum of 8.0 and above, and a hydrogenase with a pH optimum near 7.5. Carbon monoxide dehydrogenase also displays a temperature optimum near 50degreesC. When CO mass transfer is not limited during a CO uptake measurement, an extreme fast rate of CO uptake was determined, allowing for the removal of near 87% of the dissolved CO from a bacterial suspension within 10 s. This process has therefore two potential applications, one in the production of H-2 gas as a clean renewable fuel using the linked CO oxidation: H-2 production pathway, and another in using the CODH enzyme itself as a fuel-gas conditioning catalyst. These applications thereby will improve the overall H-2 economy when gasified waste biomass serves as the inexpensive feedstock. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.