The Archaea possess unique metabolic pathways, distinct from those in Bacteria and Eukarya. Based on the genome sequences of the Archaea, there are many cases in which a particular metabolic pathway seems to be absent or incomplete. The search for these ‘missing’ pathways or enzymes has been an exciting field of research in the Archaea. A representative example was the CO2-fixing mechanisms in autotrophic Crenarchaeota. Although many autotrophic Crenarchaeota had been isolated, homologs of previously recognized CO2-fixing pathways could not be identified on their genomes. Genes responsible for the degradation and biosynthesis of various sugars had also been unidentified. This paper describes recent findings in archaeal metabolism, including sugar metabolism, CO2 fixation and a wide range of biosynthetic pathways. The predicted distributions of these pathways, based on genome sequence analyses, in the Archaea are also discussed. These investigations will help understand how microorganisms use and interact with the many natural and man-made compounds they encounter in their environments and also provide the foundation for many biotechnology developments.
Novel metabolic pathways in Archaea, Curr Opin Microbiol. May 23 2011 doi:10.1016/j.mib.2011.04.014
The Archaea harbor many metabolic pathways that differ to previously recognized classical pathways. Glycolysis is carried out by modified versions of the Embden-Meyerhof and Entner-Doudoroff pathways. Thermophilic archaea have recently been found to harbor a bi-functional fructose-1,6-bisphosphate aldolase/phosphatase for gluconeogenesis. A number of novel pentose-degrading pathways have also been recently identified. In terms of anabolic metabolism, a pathway for acetate assimilation, the methylaspartate cycle, and two CO(2)-fixing pathways, the 3-hydroxypropionate/4-hydroxybutyrate cycle and the dicarboxylate/4-hydroxybutyrate cycle, have been elucidated. As for biosynthetic pathways, recent studies have clarified the enzymes responsible for several steps involved in the biosynthesis of inositol phospholipids, polyamine, coenzyme A, flavin adeninedinucleotide and heme. By examining the presence/absence of homologs of these enzymes on genome sequences, we have found that the majority of these enzymes and pathways are specific to the Archaea.