Microorganisms In The Natural Environment

Organisms live in environments with constant exchange of ions for balancing the varying osmotic pressure. They alter their intracellular ion concentration by transporting in and pumping out ions through ion channels. This action helps the organisms in maintaining ambient water level and osmotic pressure with respect to the external environment. If ion concentration exceeds far from the reach of organism’s adaptability, water will move out causing the proteins to denature and eventually die. However, some organisms are known to thrive in conditions ranging from moderately saline to extremely saline and they are referred as halophiles [1]. These halophiles form a part of large group known as extremophiles, which also includes thermophiles (living

Usually solutes like Glycine-Betaine and trehalose are present in yeast extract and thus they can be accumulated by the microbes [13]. But in the natural environment, compatible solutes can be released upon death of organisms or during efflux processes, rendering these compounds accessible to others that can scavenge them for osmoadaptation or as carbon source, provided they have the appropriate mechanisms for their uptake and catabolism. In some cases, the uptake systems are crucial for microorganisms that do not have the machinery to synthesize appropriate compatible solutes. In addition, a sudden dilution of the environment by rain or flooding triggers the release of compatible solutes. Some compatible solutes are synthesised by specialised pathways. For example, the biosynthesis of ectoine starts with an intermediate in amino acid metabolism, aspartate semialdehyde that is converted to L-2, 4-diaminobutyric acid (DABA). DABA is a cationic molecule and it has no protective role in cell. However, the next intermediate in the biosynthesis of ectoine, Nγ-acetyldiaminobutyric acid (NADA), is zwitterionic and it can act as a suitable osmolyte in Halomonas elongata strains selected for the loss of the ectoine synthase [14]. Sometimes the compatible solute that is accumulated in one microbe can be synthesised in another. For example, in most cells where it is detected, the betaine is transported into the cells from the

These uncharged compatible solutes are majorly distributed in eukaryotes like algae, fungi and higher organisms. Only four major uncharged compatible solutes are present in bacteria and archaea. They are glucosyl glycerol, mannosylglyceramide, N-carbomyl glutamine amide and N-acetylglutaminylglutamine [19]. Carbohydrates acting as a compatible solute will always get its reducing ends modified so that they do not interfere with normal metabolism. Trehalose is a nonreducing glucose disaccharide that occurs in a wide variety of organisms, from Bacteria and Archaea to fungi, plants, and invertebrates. It protects numerous biological structures against various kinds of stress, including desiccation, oxidation, heat, cold, dehydration, and hyperosmotic conditions. In addition, trehalose is a source of carbon and energy and a signaling molecule in specific metabolic pathways. It is present in organisms such as Mycobacterium tuberculosis, Corynebacterium glutamicum, and Thermus termophilus [20]. Sucrose is a non-reducing disaccharide of glucose and fructose that is widely distributed in plants. In prokaryotes, however, only freshwater and marine cyanobacteria as well as some proteobacteria are known to accumulate it. In these bacteria sucrose behaves as a compatible