Details for Archaeoglobus

Archaeoglobus was isolated from hot marine sediments near hydrothermal vents and couples the oxidation of H₂, lactate, pyruvate, glucose, or complex organic compounds to the reduction of sulfate to sulfide. Cells of Archaeoglobus are irregular cocci and cultures grow optimally at 83°C. However, one of the most remarkable features of Archaeoglobus is its relationship to methanogens. The unique biochemistry associated with methanogens involves, briefly, the use of novel coenzymes like Factor-420, coenzyme M, and many others; thus far, these novel biomolecules have only been found in cells of methanogens. Surprisingly, however, Archaeoglobus contains traces of these coenzymes and cultures of this organism actually produce small amounts of methane during growth. Thus, Archaeoglobus, which also shows a rather close phylogenetic relationship to methanogens, may represent an evolutionary transitional type of organism among the Archaea, one that bridged the energy-generating processes of sulfur reduction and methanogenesis.

More information on methanogenesis by Archaeoglobus has emerged from the complete genome sequence of this organism (Archaeoglobus fulgidus). The sequence has revealed that although Archaeoglobus can make methane, it lacks genes for a key enzyme of methanogenesis found in methanogens, methyl-CoM reductase. Thus, the small amounts of methane that are made by Archaeoglobus do not come from the activity of this enzyme, and their exact origin is unclear. The genome of Archaeoglobus contains about 2400 genes and, interestingly, shares a number of genes with species of methanogens. However, the Archaeoglobus genome sequence also reveals a number of unique genes. This suggests that genetic Archaea is quite extensive and that analysis of the genome of Archaea will likely mimic the findings of the genome projects of various Bacteria: Each new organism sequenced has about one quarter of its genes as unique genes, never before seen in other organisms.