Thermophiles lipids

In halophilic (salt loving), thermophilic, and rneth-anogenic bacteria, most of the lipids present are either... 

Figure 7.29. Structures of some membrane lipids found in the Archaea. These lipids are able to form stable monolayers. (A) A tetraether lipid, diphytanylglycosylglycerol. (B) A tetraether lipid of an extreme thermoacidophile, Sulfolobus sulfataricus. C40H72-so denotes the two biphytanyl chains (including 0 to 3 cyclopentanes). In thermophilic members of the Archaea, the ratio of tetraether lipids to diether lipids rises with increasing temperature. (Figure modified after Hazel and Williams, 1990.)...

Extremophilic bacteria employ mechanisms analogous to those used by thermophilic members of the Archaea. In some anaerobic thermophilic bacteria, C30 dicarboxylic acids may provide 10-20% of the acyl chains of membrane lipids (Langworthy and Pond, 1986). These acyl chains may be esterified to a glycerol molecule at each end of the C30 chain to form a membrane-spanning lipid with a high ability to stabilize the membrane against thermal perturbation. 

Langworthy, T.A., and J.L. Pond (1986). Membranes and lipids of thermophiles. In Thermophiles General, Molecular, and Applied... 

Langworthy TA, Pond JL (1986) Membranes and lipids of thermophiles. In Brock TD (eds) Thermophiles General, molecular and applied microbiology. Wiley Interscience, New York, p 107... 

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). 

Metallosphaera sedula [79h], which represents a new genus of aerobic metal-mobilizing thermophilic archaea in the order Sulfolobales, was found to contain a similar pattern of caldarchaeol and nonitolcaldarchaeol-derived glycolipids and the corresponding P-inositol phosphoglycolipids to those of Sulfolobus solfataricus (e.g., see structures 38, 38A, 44 and 44B, Fig. 8 [75,79]). However, the relative proportions of the major glycolipids (38 and 44) and the minor complex lipids of M. sedula differ somewhat from those of S. solfataricus. 

Despite the limited number of extreme thermophile species that have been examined for lipids, it appears that a few genera. Thermoplasma, Sulfolobus, Thermoproteus, Desulfurococcus, Thermococcus and Pyrococcus may be distinguished by their glycolipid and phosphoglycolipid compositions. However, it should be noted that genera in the Order Sulfolobales examined so far, such as Sulfolobus, Desulfurolobus and Metallosphaera have very similar lipid patterns, and it would be difficult to differentiate between them on the basis only of their lipids. 

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

A section on protein structural chemistry in archaea includes Chapters 5 through 7, respectively, by D. Oesterhelt on the structure and function of photoreceptor proteins in the Halobacteriaceae J. Lanyi on the structure and function of ion-transport rhodopsins in extreme halophiles and R. Hensel on proteins of extreme thermophiles. In a section on cell envelopes (Chapters 8-10), O. Kandler and H. Konig discuss the structure and chemistry of archaeal cell walls M. Kates reviews the chemistry and function of membrane lipids of archaea and L.I. Hochstein covers membrane-bound proteins (enzymes) in archaea. 

The fact that Sulfolobus and Thermoplasma have similar lipids is of interest, but almost certainly this can be explained by convergent evolution. This hypothesis is strengthened by the fact that Halobacterium, another quite different organism, also has lipids similar to those of the two acidophilic thermophiles. [14]... 

In the synthetic direction, an artificially applied has been shown to result in net ATP synthesis when the purified complex from the thermophilic bacterium PS3 was incorporated into a synthetic lipid bilayer vesicle [18]. 

We close this survey of cell membranes with a remarkable observation that adds support to this novel picture of cytomembrane shape. In Chapter 4 (section 4.13), it was noted that many bacteria are shrouded in a mesh-like protein coat, which often displays a regular, crystallographic form. The most exotic examples of bacteria are the thermophilic archaebacteria, that thrive at temperatures between 70°-105°C, in sulfur-rich hot-springs and mud holes. (So anachronistic are these single-celled organisms, that they are sometimes taxonomically classified as a distinct Kingdom.) It appears that the dimensions of the protein layers in species of these bacteria, Solfolobus solfataricus, are in "precise epitaxial coincidence" with the lattice parameters of a bicontinuous cubic phase, formed in excess water with the membrane lipids predominant in this organism in vitro) [140]. Such a coincidence is indeed difficult to reconcile with the usual notion of a flat, neutral, cytomembrane, whose sole function is to support the real stuff of life, the proteins. 

Nakano, K. and Matsamura, M. (2001). Improvement of treatment efficiency of thermophilic oxic process for highly concentrated lipid wastes by nutrient supplementation.. Biosci. Bioeng. 92(6), 532-538. 

A limited improvement in this context may be possible by the use of more stable proteins, e.g. from thermophilic bacteria. However, many principles demonstrated by nature could be transposed to sensor development. For example, biomimetic channel and carrier molecules could be used in conjunction with stabilized lipid membranes to prepare sensitive and selective electrochemical transducers which embodied the principle of intrinsic amplification by depolarization. The use of artificial receptor sites would probably result in a substantial reduction of the desired selectivity coefficients, but this could easily be compensated by the application of array processing for background correction. 

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