Environment hypersaline

Other physiological functions of MAAs in phototrophic organisms such as organic osmolytes have been suggested, because very high concentrations can be found in cyanobacteria living in hypersaline environments (Oren 1997). However, salt shock experiments with the marine cyanobacterium Microcoleus chthono-plastes did not indicate ary major involvement of MAAs in the process of osmotic acclimation (Karsten 2002), and hence their proposed function as osmolytes has to be questioned. 

Brominated fatty acids are rare in nature. They have been found in sponges and other marine animals. Recently, the presence of (5E, 7E)-18-bromo-octadeca-5,17-diene-15-ynoic acid (221) and 18-bromo-octadeca-5,7,17-triynoic acid (222) has been described in a halophilic (present in hypersaline environments) terrestrial organism, the Central Asian lichen Acorospora gobiensis [171]. 

There are, however, some problems in the direct application of such a ratio. First, relative high abundances of A7-sterols have been reported in Lake Kinneret, a normal marine salinity environment (39). Hence, A -sterols are obviously not restricted to organisms living in hypersaline environments. The relative abundance of A7- (and a8 14)-) sterols in hypersaline environments may be due to the absence of grazing zooplankton in these environments. In normal marine salinity environments A7- and A8(14)-sterols are selectively metabolised in the guts of zooplankton resulting in a selective preservation of A5-sterols in zooplankton fecal pellets, which are transported rapidly to the sediment (40,41). 

A more critical evaluation of the above mentioned ratios and phenomena reveals the usefulness of the various palaeosalinity indicators. Distribution patterns of methylated chromans and the relative abundance of gammacerane are not influenced by sulfur incorporation reactions and may directly reflect species distributions in the palaeoenvironment. To some extent this holds for 14a(H),17a(H)/140(H),170(H)-steraneratios as well, although incorporation of sulfur may influence this ratio and original A7/A5-sterol ratios do not always correlate with hypersaline environments. The isoprenoid thiophene ratio is highly useful as a palaeosalinity indicator since the distribution of the C20 isoprenoid thiophenes directly reflects the distribution of their substrates. The other parameters (pristane/phytane ratio, odd-over-even carbon number predominance of n-alkanes, relative abundance of C35 hopanes and/or hopenes) should be used with caution because they obviously depend on the quenching by sulfur of specific lipids, a process which is not restricted to hypersaline environments. 

Gorbushina, A. A. Krumbein, W. E. (1999). Poikilotrophic response ofmicro-orgamsms to shifting alkalimty, salinity, temperatme and water potential. In Microbiology and Biogeochemistry of Hypersaline Environments, ed. A. Oren. London CRC Press, pp. 75-86. 

Highly saline environments are not only directly associated with present seas and oceans, but also with former seas which have led to salt deposition. These are generally hypersaline environments and may include salt lakes such as the Dead Sea, where salt concentrations may reach 4-5 M NaCl (Buchalo et al., 1998), together with salt pans and flats. In many cases, these are dominated by other ions such as potassium, magnesium, calcium, sulphate, carbonate and bicarbonate, as well as sodium and chloride. Flowers et al. (1986) estimated that about 10% of global land area was occupied by soils too saline for the growth of non-halophiles. 

The Halobacteriaceae, commonly referred to as the halobacteria, are a family of extremely halophilic archaebacteria [113]. As in other archaebacteria, their membranes contain ether-linked lipids. The primary lipids present are diphytanyl phospholipids [113]. Their cell walls are also unique in structure and lack muramic acid. There are several species of halobacteria that vary considerably in their physiological characteristics. The halobacteria are unicellular rods or cocci. More recently flat, square and box-shaped cells have been described. Halobacteria are found growing in salterns or natural salt lakes and on the surface of salted fish. They often form dense planktonic blooms and can form massive accumulations on solid substrates. They may be involved in mat communities in hypersaline environments. 

Variants of the diphytanylglyceroldiether (1) found in some archaea are as follows (a) both the C20-C25 diether (structure lA, Fig. 1) and C25-C25 diether (structure IB) core lipids occur in alkaliphilic species of extreme halophiles Natronobacterium and Natronococcus)[30, il, and the C20-C25 diether (lA) also occurs in Halococci[32 and in Halobacterium, Haloferax and Natronobacterium strains from hypersaline environments in India [33] (b) a macrocyclic C4o-diether (structure 1C, Fig. 1) [34] is... 

Mejanelle L., Lopez J. F., Gunde-Cimerman N., and Grimalt J. O. (2000) Sterols of melanized fungi from hypersaline environments. Org. Geochem. 31, 1031-1040. 

Several methanogens capable of using DMS have been isolated from marine and hypersaline environments (Finster et al., 1992 Kiene et al., 1986 Oremland et al., 1989 Rajagopal and Daniels, 1986), and a freshwater methanogen with this capability has also been isolated and represents a new genus (Lomans ef a)., 1999b). The degradation of DMS and MeSH appears to occur... 

Cyanobacterial mats in modem hypersaline environments also release significant quantities... 

Open-ocean waters have a narrow range of salinities (32-37) and most are near 35. In estuaries, values fall to less than 1 approaching the freshwater end-member. In hypersaline environments salinities can exceed those of seawater, reaching values greater than 300. 

R. F. Shand L. B. Price E. M. O Connor, Halocins Protein Antibiotics from Hypersaline Environments. In Microbiology and Biogeochemistry of Hypersaline Environments A. Oren, Ed. CRC Press Boca Raton, 1999, pp 413-424. 

H. and Barter, S.R., 1993. Carbohydrate diagenesis in hypersaline environments Application of GC-IRMS to the stable isotope analysis of derivatives of saccharides from surficial and buried sediments. Org. Geochem., 20 927-933. 

As salinity of waters is mostly caused by chlorides (NaCl), the organisms which are able to live in hypersaline environments are named halophilic... 

R Ciulla, MR Diaz, BF Taylor, MF Roberts. Organic osmolytes in aerobic bacteria from Mono Lake, an alkaline, moderately hypersaline environment. Appl Environ Microbiol 63 220-226, 1997. 

Evaporite deposits are sources of solutes that are the most important to consider with reference to microbial proliferation. Saturated brines of NaQ ( 5/2 M), where the aw = approximately 0.75, are relatively conunon on Earth and diverse microorganisms, including members of the Bacteria, Archaea, and Eukarya, are known to maintain stable populations in these hypersaline environments by regularly undergoing cell division [32]. 

---