Methanogens lipids

Methanogen lipids have been intensively studied and characterized due to their structures being one of the most remarkable features that distinguish the Archaea from all other organisms (Woese et al., 1990). The polar lipids of methanogens comprise both di- and tetra-ethers of glycerol and isoprenoid alcohols with most compounds being based on the core lipids archaeol (12) or caldarchaeol (13). Minor core lipids are sn-2- and i -3-hydroxyarchaeol and macrocyclic... 

Marine algae as well as aquatic higher plants accumu- phospholipids, methanogens contain diphytanyl late arsenophospholipids.30 tetraether lipids that are both glycerophospholipids... 

Risatti, J.B., Rowland, S.J., Yon, D., and Maxwell, J.R. (1984) Sterochemical studies of acyclic isoprenoids—XII. Lipids of methanogenic bacteria and possible contributions to sediments. In Advances in Organic Geochemistry (Schenck, P.A., and de Leeuw, J.W., eds.), pp. 93-103, Pergamon Press, Oxford, UK. 

It should be noted that the extreme halophiles contain only archaeol-derived lipids, the methanogens contain both archaeol-and caldarchaeol-derived lipids, in about 2 1 to 1 1 proportion, respectively, and the thermoacidophiles contain largely caldarchaeol- and nonitolcaldarchaeol-derived lipids, with a maximum of 1-10%a of archaeol-derived lipids[4,10,21,27,28]. 

Fig. 2. Dibiphytanyidiglyceroltetraether (2, caldarchaeol), dibiphytanyl glycerol nonitol tetraether (2A, nonitolcaldarchaeol), and various cyclized derivatives (2B-2I, cyclized caldarchaeols and nonitolcaldarchaeols) core lipids in thermoacidophiles and some methanogens [10,12,20].

Studies of the lipids of four families of methanogens [58-60] have identified the archaeol analogs of phosphatidylinositol (API, 14, Fig. 6) [61], phosphatidyl-ethanolamine (APE, 15, Fig. 6) and phosphatidylserine (APS, 16, Fig. 6), as major components in Methanobacteriaceae but not in Methanomicrobiaceae, and Methanosarcinaceae, and only APS (16) was found in Methanococcaceae. Another phospholipid, caldarchaeolphosphoethanolamine (CPE, 34, Fig. 7) was found only in the genera Methanobacterium and Methanosarcina. 

Lipids of the thermophilic deep-sea methanogen, Methanococcus jannaschii [67] are based largely on the macrocyclic diether (cyc-archaeol, 1C) and consist of mono- and di-glucosyl-cyc-archaeol (20A, 23A, respectively. Fig. 6), P-ethanolamine-glucosyl-cyc-archaeol (20B) and cyc-archaeol-PE (15A) a small amount of archaeol-PE (15) is also present. Mco. Jannaschii is also capable of forming caldarchaeol-derived polar lipids [68], and the proportions of diether, macrocyclic diether and tetraether lipids can vary as a function of growth temperature (see section 5.2). 

Another methanogen, Methanococcus jannaschii, isolated from a deep-sea hydrothermal vent at temperatures of 85 C or higher, has membrane lipids based on cyc-archaeol (1C), which was not found in any other species of methanogens surveyed and may be unique to methanogens from deep-sea hydrothermal vents [34,67]. It is possible that the presence of cyc-archaeol-based lipids may be related to the high pressures under which these deep-sea methanogens live. 

Fig. 14. Proposed evolutionary relationships between extreme halophiles, methanogens and extreme thermophiles based on lipid composition.

Koga Y., Nishihara M., Morii H., and Akagawa-MatsushitaM. (1993) Ether polar lipids of methanogenic bacteria structures, comparative aspects, and biosynthesis. Microbiol. Rev. 57, 164-182. 

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