Hydrogen Metabolism in Syntrophic Microorganisms

Acetomicrobium hydrogeniformans OS1 is an obligate anaerobic bacterial species of the phylum Synergistetes that generates an unusually high molar ratio of hydrogen from glucose, thus suggesting an undescribed metabolic ability relative to other hydrogen-forming bacteria. Here, the genomic, proteomic, and enzymatic basis of glucose fermentation in A. hydrogeniformans is examined. A modified Embden-Meyerhoff pathway was revealed that employs a glyceraldehyde-3-phosphate oxidoreductase enzyme (GAPOR) in place of glyceraldehyde-3-phosphate dehydrogenase (GapA) and glycerate kinase (Pkg). A. hydrogeniformans cell extracts exhibited GAPOR as well as pyruvate-ferredoxin oxidoreductase (PFOR) activity in place of GapA, Pgk, pyruvate dehydrogenase (Pdh), or pyruvate formate lyase (Pfl) activity that would generate acetyl-CoA and NADH. Proteomic and enzyme studies revealed that electrons derived from GAPOR and PFOR drive hydrogen formation by a soluble FeFe-type hydrogenase. These A. hydrogeniformans findings demonstrate the presence of an unconventional C6 metabolism that would explain the high hydrogen production. This is the first demonstrated example of GAPOR in the Bacteria where this enzyme is typically found only in thermophilic archaea. Bioinformatics comparisons to related Acetomicrobium strains plus other genera of the phylum Synergistetes suggest this modified pathway is also present in other Synergistetes species. This dissertation also includes an examination of the genome of a methanogenic archaeon, Methanospirillum hungatei