Molecular biology of methanogens.

Methanogens are a very diverse group of the Archaea (Archaebacteria). Their genomic DNAs range from 26 to 68 mol% G+C; they exhibit all known prokaryotic morphologies and inhabit anaerobic environments as varied as the human gut and deep-sea volcanic vents. They are, nevertheless, unified by their ability to gain energy by reducing CO, CO2, formate, methanol, methylamines, or acetate to methane. Methanogen genes are reviewed and analyzed in terms of their organization, structure, and expression and are compared with their bacterial (eubacterial) and eukaryal (eukaryotic) counterparts. Many methanogens are thermophiles, and some are hyperthermophiles. The influence of these extreme environments on their macromolecular structures is also addressed. Methanogens are oxygen-sensitive, fastidious anaerobes, and therefore their experimental manipulation in research laboratories has been very limited. The majority of the information currently available describing their molecular biology has been gained by gene cloning. With improvements in anaerobic handling procedures, this is beginning to change, and several experimentally tractable regulated systems of gene expression in methanogens are discussed. Anaerobic biodegradation terminating in methane biogenesis is an established, economically very important biotechnology used world-wide both to reduce waste and to generate fuel-grade biogas. The substantial progress made over the past decade, reviewed here, in understanding the molecular biology of methanogens should now provide a data base for considering genetic approaches to improving this process.