Electron microscopic images of N. thermophilus strain JW/NM-WN-LFT field emission scanning electron micrograph of aldehyde-fixed, acetone dehydrated and critical ponit-dried cells of strain JW/NM-WN-LFT revealed a rod-like appearance with variable length of single cells.

The poly-extremophile Natranaerobius thermophilus is able to grow in batch culture between 30 and 57°C, with an optimum at 53°C. N. thermophilus is an obligate alkaliphile, the pH55°C range for growth is 8.5-10.6, with an optimum at pH55°C 9.5. N. thermophilus is also an obligate halophile; it grows optimally between 3.3 and 3.9 M Na+ (1.7-2.3 M added NaCl), the Na+ range for growth being 3.1-4.9 M (1.5-3.3 M of added NaCl). N. thermophilus is obligately anaerobic, utilizing fructose, cellobiose, ribose, sucrose, trehalose, trimethylamine, pyruvate, casamino acids, acetate, xylose, and peptone as carbon and energy sources. Fumarate (20 mM), S2O32- (20 mM), NO3- (20 mM), and Fe III citrate (20 mM) are utilized as electron acceptors. During growth on sucrose, the isolate produced acetate and formate as major fermentation products. Cells of N. thermophilus are rod-shaped, non-motile and non-sporeforming. Main cellular fatty acids are iso-branched 15:0, i17:0 dimethyl acetal and 16:0 dimethyl acetal. The G+C content of genomic DNA was 40.4% (determined by HPLC). Phylogenetically, N. thermophilus forms a novel lineage within the class Clostridia, and belongs to the novel family Natranaerobiaceae and novel order, Natranaerobiales (Mesbah et al, 2007).

As regards to habitat, N. thermophilus was isolated from sediment of alkaline, hypersaline Lake Fazda located in the Wadi An Natrun, Egypt. Other Natranaerobius spp. have been isolated from other alkaline, hypersaline lakes in the Wadi An Natrun and the Kenyan-Tanzanian Rift.

The unique growth characteristics of N. thermophilus places it within a unique group of extremophiles termed the halophilic alkalithermophiles. The halophilic alkalithermophilic bacteria are a novel group of extremophiles that have been recently recognized (Kevbrin et al. 2004). They are adapted to grow at a combination of three extreme environmental conditions, elevated temperature, alkaline pH and elevated NaCl concentration, an evolutionarily interesting combination. There is little information on the genes and molecular machines that allow for a haloalkalithermophilic lifestyle. It is assumed that haloalkalithermophiles combine adaptive mechanisms of halophiles, alkaliphiles and thermophiles. However it is difficult to reconcile specific adaptive mechanisms with each other (Konings et al. 2002, Vossenberg et al, 1999a, 1999b, Prowe et al, 1996, Yumoto et al., 2000). Genome sequence data for these microorganisms will lead to identification of gene features required for life under multiple extreme conditions. The genomic sequence will also facilitate future functional genomic studies involved in characterization of novel biochemical, physiological and metabolic properties responsible for microbial survival, adaptation and growth in extreme environments. In addition, elucidation of adaptive mechanisms of multi-extremophilic microorganisms will extend the present understanding of the boundaries under which life can exist and will provide excellent models for the study of adaptive mechanisms to extreme environmental conditions.

Availability of a genome sequence for a haloalkalithermophile will also contribute to the field of astrobiology and will help in evaluating some of the presently available hypotheses on the origin of life. These include the theory that life evolved in shallow saline and alkaline pools on available clay or mineral surfaces such as pyrite (Zavarzin, 1993). This statement is based on that life probably occurred at moderately elevated temperatures, the Hadean Ocean was probably alkaline and that Mars possibly has a brine channel subsurface (www. Nssdc.gsfc.nasa.gov/planetary/marslife.html).

Sequencing the genome of a multi-extremophile will also impact biotechnology. Haloalkalithermophiles are potential sources of enzymes uniquely adapted to activity at high salt concentrations, pH and high temperatures. Truly halophilic enzymes are inactivated and denatured at concentrations less than 1M NaCl (Adams and Kelly, 1995). Their combined thermostability makes them of enormous commercial potential in high salt, high temperature industrial processes. These “extremozymes” have the additional advantage of being more stable to detergents, organic solvents and chaotropic agents than mesophilic enzymes.

References

Adams, M. W. and R.M. Kelly. 1995. Enzymes from microorganisms form extreme environments. Chem. Eng. News. 73: 32-42.

Kevbrin, V.V., C.S. Romanek and J. Wiegel. 2004. Alkalithermophiles: A double challenge from extreme environments. p. 395-412. In J. Sechbach (ed.), Cellular Origins, Life in Extreme Habitats and Astrobiology. Vol. 6. Kluwer Academic Publishers, Dordrecht.

Konings, W. N., S.-V. Albers , S. Koning, and A. J. M. Driessen. 2002. The cell membrane plays a crucial role in survival of bacteria and archaea in extreme environments. Antonie van Leeuwenhoek 81:61-72.

Mesbah, N. M., D.B. Hedrick, A.D. Peacock, M. Rohde, and J. Wiegel. 2007. Natranaerobius thermophilus gen. nov. sp. nov., a halophilic, thermophilic bacterium from Wadi An Natrun, Egypt, and proposal of Natranaerobiaceae fam. nov. and Natranaerobiales ord. nov. Int. J. Syst. Evol. Microbiol. 57: 2507-2512.

Prowe, S., J. van de Vossenberg, A. Driessen, G. Antranikian, and W. Konings. 1996. Sodium-coupled energy transduction in the newly isolated thermoalkaliphilic strain LBS3. J. Bacteriol. 178:4099-4104.

Vossenberg, J. L. C. M. v. d., A. J. M. Driessen, D. Grant, and W. N. Konings. 1999. Lipid membranes from halophilic and alkali-halophilic Archaea have a low H+ and Na+ permeability at high salt concentration. Extremophiles 3:253-257.

Vossenberg, J. L. C. M., A. J. M. Driessen, M. S. da Costa, and W. N. Konings. 1999. Homeostasis of the membrane proton permeability in Bacillus subtilis grown at different temperatures. Biochim. Biophys. Acta 1419:97-104.

Yumoto, I., K. Yamazaki, M. Hishinuma, Y. Nodasaka, N. Inoue, and K. Kawasaki. 2000. Identification of faculatatively alkaliphilic Bacillus sp. strain YN-2000 and its fatty acid composition and cell-surface aspects depending on culture pH. Extremophiles 4:285-290.

Zavarzin, G. 1993. Epicontinental soda lakes are probable relict biotopes of terrestrial biota formation. Microbiology. 62:473-479.