Role of L - Glutamate in the Tolerance of Osmotic Stress by Escherichia coli

of medium osmolarity are generally deleterious to bacterial cell growth. The ability of organism to adapt to osmotic stress is a fundamental biological process that protects them against fluctuations in water activity and solute content in their environment 1. Many organisms including bacteria, yeast, plants and animals can adapt to various hyperosmotic stress by accumulating low-molecular-mass organic compounds known collectively as osmolytes 2. Intracellular accumulation of osmolytes either by de novo synthesis or by transport from the growth medium confers tolerance to hyperosmotic stress 1,3-4. It is well established that the intracellular accumulation of these solutes prevents water loss and maintains the turgor pressure of the cell essential for the cell growth. These molecules also stabilize the native state of various globular proteins against denaturing stresses and favour formation of protein assemblies 2,5. By themselves, these solutes do not perturb the functional activity of macromolecules and hence are compatible with protein function 1,6-8. While L-isomers of amino acids are predominantly found in all living organisms, D-amino acids in general 9 are also not uncommon in nature 10. Cell walls of Gram-negative bacteria contain D-alanine, antibiotic peptides contain D-amino acids 11. Many invertebrates have free D-amino acids in their body fluids that are known to participate actively in metabolism 12-14. D-Enantiomers of amino acids have also been detected in human physiological fluids 15. However, under stressed conditions, living organisms are known to accumulate only L-isomers of amino acids while no D-amino acid has been found to accumulate till date. Why living organisms have evolved to select only L-amino acids, as naturally occurring osmolytes is a matter of debate. The purpose of this present study is to examine the effects of physiological stress on the pattern of proteins synthesized by E. coli and to investigate the effect of L-glutamate on counteracting osmotic stress. The four environmental isolates (E1, E2, E3 and E4), four clinical isolates (C1, C2, C3 and C4) and one ATCC strains of E. coli were used in this study. A minimal medium was used to support the growth of the organisms so that the medium ingredients would not interfere by contributing any protein to the cell extract. The minimal media was prepared mixing two separate solutions. Solution A contains 7.0 g K 2 HPO 4 , 3.0 g KH 2 PO 4 , 0.1 g Na-citrate.2H 2 O, 0.1 g Mg SO 4. 7H 2 O, 1.0 g (NH …