Halophiles usually thrive in salty environments and they are categorized according to the extent of their tolerance for highly saline environments, ranging from slight, moderate and extreme. Their adaptability to these highly saline environments, which have limited habitation by life forms, has drawn the interest of scientists who seek to understand the biochemical mechanisms involved under such conditions for possible usage of their enzymes (Ollivier, Hatchikiern, Precier, Guezennec, and Garcia 50). The organism H. Halobium has a membrane structure design that makes the optimal habitat for it a hyper saline environment. The salinity of the water bodies can be attributed to the high rates of evaporation due to high temperatures
The habitats for halophiles as already indicated, are characterized by variability in composition ranging from high salt content of up to 8.9 to 10% (wt/vol) together with high pH levels of 9 to 10 (Oremland and King 181), while others exhibit salt concentration of up to 20 % (wt/vol) with pH levels of 7. The halophile H. Halobium is found in the Great Salt Lake, which is a hyper-saline eco system. The conditions for this environment will encompass up to the 20 % salt concentration with the pH of 7.
The predominant ions in the Great Salt lakes and similar habitats are Na+ and Cl–, with Na+ having a concentration of 105.4 whilst Cl– is 181g/liter. This high concentration of NaCl makes oxidation of organic substances incomplete compared with other ecosystems. Besides these two ions, however, there are other ions like the sulphate ion, though at low levels due to precipitation in this lakes, which acts as an important electron acceptor and aids in the mineralization of organic matter in the ecosystems. It also has Ca+ at a concentration of 17.2g/liter which is an important divalent cation similar to Na+.
The habitat envisaged for H. Halobium also has a concentration of organic matter which is a result of the dead cells of the metabolites of the Halophiles growing in the water, and which raises the concentration of salt in the habitat to an extent that the vegetation growing nearby would die if the water levels were raised by an occurrence like rainfall to reach their growth and consequently submerge them like the case reported once in a hyper saline African lake ( Ollivier, Caumette, Jean-louis mah 28). The organic matter also originates from the algae and vegetation growing on the banks of the lakes. Therefore, the limited biodiversity of this environment would only allow methanogenic species of the archaea, like the halobacteria, to survive at the NaCl concentration of 20% exhibited in these hyper saline lakes. The key to survival in this otherwise hostile environment is the ability to adapt to various conditions presented to the H. halobium cells.
A crucial composition of the plasma membrane surrounding the organism is the ether lipids which are unique for purposes of maintaining homeostasis in the organism. The lipids have branched and saturated fatty acids which are different than other organisms. They are characterized by ether bonds and branched by isoprenoid chains rather than ester bonds and fatty acyl chains as found in other organisms. These lipids are much more stable than other organisms making them able to survive in extreme conditions. Phospholipid Archaetidyglycerol methylphosphate (PGP-Me) is another key composition of the membrane that makes the cell membrane more stable in the prevailing saline conditions. Large unilamellar vesicles (LUV), produced by the polar lipids retain carboxyfluorescein, this further counteracts the effects of the saline environment within the range of 0-5 m NaCl; giving the cell its rod-like shape. H. halobium maintains a large surface of lamellar within the lipid that displays stability, when exposed to high temperatures of up to 100 degrees Celsius. PGP-Me in the lipid layers has a dual charge that gives the cell stability via its electrostatic repulsion forces.
The S-layer of H. halobium is a two dimensional crystal structure, formed from S-layer glycoproteins. The two dimensional structure produces a matrix of glycans structures. The cell layer has to protect the membrane against extreme osmotic conditions. The S-layer contains two proteins namely: SlaA and SlaB. These proteins interact with each other in a process called glycosylation, to remain anchored to the main cell membrane. The S-layer also, helps in the glycosynthesis process of the cell; enabling a bacterial generation time of 20 seconds. The S-layered glycans are also important for typing strains of the H. Halobium. This layer also has the ability to adapt to various environmental changes.
H. Halobium has adapted to its hyper saline habitat in such a way that allows it to overcome problems caused by osmotic pressure. The organism defeats osmotic pressure by producing a solute that is positively charged. The cell produces positively charged K+ ions that counteract the effects of the saline environment. The ions make the cell isotonic to the saline habitat around it (Mescher, Strominger 2009). Water usually diffuses out of their bodies to the environment due to the hyper saline condition. Other organisms would die if subjected to such environments but H. Halobium is able to prevail.
The surface proteins of H. Halobium are negatively charged as a result of a high ration of basic to acidic amino acids allowing the proteins to be solvated in its hyper saline habitat and to further prevent denaturation, aggregation and denaturation. Another important protein that H. Halobium contains is the bacteriordhodopsin, which is found in arrays within the cell membrane. This protein is a pigment that functions as chlorophyll in green plants. It uses light from the sun as energy to pump protons across the cell membrane. This has an effect of causing the internal environment to be more alkaline than the surrounding environment. To add on this, H. Halobium also has a unique feature in its membrane to help in locating areas in the water with high concentration of oxygen. This feature includes novel gas vesicles which enable the organism to float in the water to tap oxygen from the environment, or if there is a need for more stable salt concentrations, it allows H. Halobium to sink deep into the water in areas where the salinity is optimum (Studier 240).
From the examination of existent habitat and membrane design of the H. halobium explored in this paper, it can be seen that the organism is very unique in composition, different from many other organisms because the saline habitat presents very severe living conditions and therefore leaving it with option adaptation. From the ionic composition, salinity and pH, to the unique features of the membrane and other adaptive features, a clear picture is shown on how to design the membrane and habitat of the organism.
Works cited
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Ollivier, E., Garcia J. L., Guezennec J., Hatchikiern C. E., and Prensier G. “A halophilic sulfate-reducing bacterium from sediments of a hyper saline lake in Senegal.” Int. J. Syst. Bacterial 41:7481 (1991). Web.
Oremland, R. S., and King, G. M.. “Methanogenesis in hyper saline environments”. In Y. Cohen and E. Rosenberg (ed.), Microbial mats: physiological ecology of benthic microbial communities. American Society for Microbiology, Washington (1989): 180-190. Web.
Studier, J. “Analysis of bacteriophage T7 early RNAs and proteins on slab gels.” J Mol Bio 79 (1973). 237–248. Web.