Extreme halophiles

Membranes of extreme halophilic (Kushwaha et al. 1975, Anwar et al. 1977, Anton et al. 2002, Lutnaes et al. 2002, Oren 2002) and thermophilic bacteria (Alfredsson et al. 1988, Yokoyama et al. 1995) contain a large concentration of polar carotenoids. Membranes of these bacteria, which live in extreme conditions, should provide a high barrier to block nonspecific permeation of polar and nonpolar molecules. Incorporation of dipolar carotenoids into these membranes at a high concentration serves this purpose well because dipolar carotenoids increase the hydrophobic barrier for polar molecules (Wisniewska and Subczynski 1998, Wisniewska et al. 2006) and increase the rigidity barrier... 

Anton, J., A. Oren, S. Benlloch, F. Rodriguez-Valera, R. Amann, and R. Rossello-Mora. 2002. Salinibacter ruber gen. nov., sp. nov., a novel, extremely halophilic member of the bacteria from saltern crystallizer ponds. Int. J. Syst. Evol. Microbiol. 52 485M91. 

Lutnaes, B. F., A. Oren, and S. Liaaen-Jensen. 2002. New C-40 carotenoid acyl glycoside as principal carotenoid in Salinibacter ruber, an extremely halophilic eubacterium. J. Nat. Products 65 1340-1343. 

Oren, A. 2002. Molecular ecology of extremely halophilic archaea and bacteria. FEMS Microbiol. Ecol. 39 1-7. 

Xerotolerant an organism capable of growth at low water activity. For example, an extreme halophile or endolith. 

In this paper, we will describe one of examples, where artificial archaeal glycolipids are applied to the construction of nano-devices containing energy-conversion membrane proteins, by employing the phytanyl-chained glycolipid we have recently developed, i.e., l,3-di-o-phytanyl-2-o- ((3-D-maltotriosyl) glycerol (Mab (Phyt)2, Fig. 1) [16,17] and natural proton pump, bacteriorhodopsin (BR) derived from purple membranes of the extremely halophilic archaeon Halobacterium salinarium S9 [18],... 

Life is more susceptible to high tenqjerature conditions. No multicellular plant or animal has ever been found to survive above 50 C and no protist is known that can tolerate long-term exposure to above 60 C. Conditions of high salinity are also very selective, allowing the growth of only extreme halophile prokaryotes, both Archaea and Bacteria (Kates 1993). 

Isoprenyi glyceryl ethers archaeol-like (archaeol Cm-C ), comprising C20-C25 and C25"C25 homologues (an extreme halophilic, thermoacidophilic, and methanogenic Archaea Kates 1993 caldarchaeol-like (caldarchaeol monocyclic C o-C ), comprising bicyclic structures from thermoacidophilic and methanogenic Archaea Kates 1993. (Archaea in bold ce are not meant to be exclusively marine). 

Enzymes do Function Without Water as a Bulk Solvent-Lessons from Extreme Halophiles... 

Let us consider first lipid-lipid interaction. Urry et al, showed the existence of a positive CD band at 218 m/x and a negative CD band at about 192 m/z in phosphatidyl choline and phosphatidyl ethanolamine dissolved in trifluoroethanol (86). The 192-m/z band was not characterized in detail, but the 218-m/z band is of such position and shape that the addition of lipid and protein CD bands could produce a composite CD band, and hence an ORD Cotton effect, which is red shifted. As noted by Urry, the 218-m/z CD extremum of lecithin must arise from n — 7T transitions in the fatty acid ester groups. Although the optical activities of solutions of deproteinized membrane phospholipids determined at the same concentration as in the intact membrane are negligibly small, in membranes an ordered array of lipids could greatly enhance rotation. Such an effect could yield information on the nature of lipid-lipid association. This can be tested experimentally. Halobacterium cutirubrum offers a unique system since Kates has shown that the lipids in this extreme halophile contain ether bonds rather than ester bonds (43, 44), Hence, the n — tt transition essential to the CD band at 218 m/z in phospholipids does not exist. Nevertheless, we found that the ORD... 

Extreme halophiles (Halobacteriaceae) K+, at concentrations that may exceed 5 M... 

Figure 6.2. (Upper panel) The four major classes of organic osmolytes (I) sugars and polyhydric alcohols (polyols) (II) amino acids and amino acid derivatives (III) methylated ammonium and sulfonium compounds and (IV) urea. (Figure modified after Somero and Yancey, 1997.) (Lower panel) Structures of charged osmolytes accumulated in extremely halophilic archaea (after Martin et al., 1999). Note that these osmolytes commonly represent a type of organic osmolyte that is found in many bacteria or eukaryotes to which a charged group has been attached. Typically, the charged group is anionic, for example, a phosphate or a carboxylate group.

The striking contrasts between the effects of salts on enzymes of extremely halophilic archaea and those of organisms in which [K+] lies in the more typical range of 0.1 to 0.2 M are evident from a comparison of data in figure 6.4... 

Figure 6.4. The effects of different inorganic salts on activity of malate dehydrogenase from an extremely halophilic archaeon (unpublished data of L. Borowitkza and G. Somero).

Unique Amino Acid Composition of Proteins of Extremely Halophilic Archaea When Folding Requires Help from Osmolytes... 

A. V. Smirnov, T. V. Kulakovskaya and I. S. Kulaev (2002a). Phosphate accumulation by an extremely halophilic archae Halobacterium salinarium. Proc. Biochem., 37, 643-649. 

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