Hydrogenases of Methanococcus maripaludis

The methanogens catalyze a major component of the Earth’s H2 cycle. They are especially active in anaerobic environments where they are the primary consumers of fermentatively produced H2. These strictly anaerobic Archaea have evolved unique adaptations to H2 metabolism, many of which are poorly understood. Our research examines the enzymes and pathways in H2 metabolism in methanogens, especially as they relate to energy conservation (Fig. 1). In addition, the metabolism of formate, from which H2 is produced, is being investigated. The model species of choice is the hydrogenotroph Methanococccus maripaludis. Transcriptome and proteome studies have determined the regulatory effects of H2 limitation. Studies of protein complexes indicate that the heterodisulfide reductase is membrane-associated and also forms a complex with certain hydrogenases and with formate dehydrogenase. The analysis of mutants has suggested that two alternative pathways function in the interconversion of reduced coenzyme F420 and H2. Finally, growth yield studies with chemostats suggest that two alternative pathways of energy conservation function under differing conditions of H2 availability. Progress report Function of the energyconserving hydrogenase Ehb and global regulation in an Ehb mutant. We constructed a mutant of Methanococcus maripaludis lacking the energy-conserving hydrogenase Ehb and obtained evidence that the mutant was deficient in biosynthetic CO2 assimilation. Microarrays and differential proteomics confirmed that the mRNA and protein levels for the enzymes of CO2