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Role of L-glutamate in the Tolerance of Osmotic Stress by Escherichia Coli

M Shariful Islam
Department of Microbiology, University of Dhaka, Dhaka 1000, Bangladesh

Sunjukta Ahsan
Department of Microbiology, University of Dhaka, Dhaka 1000, Bangladesh

Abstract/ Executive Summary:

Studies on thec ellular response to conditions of physical or chemical stress have played a very significant role in diverse areas of biology. The present investigation aims at determining concentrations of NaCl that are stressful for environmental and clinical strains of Escherichia coli and to investigate the effect of L-glutamate to counteract such stressful conditions. It was observed that growth of environmental, clinical and reference strains could be stressed by a NaCl concentration of 0.9 M. Growth decreased under conditions of stress as opposed to that without added NaCl. Clinical isolates showed much higher resistance than environmental strains to osmotic stress. Glutamate had a significant effect in overcoming osmotic stress under laboratory conditions. This was indicated by increased growth in the presence of glutamate (15 mM) compared to that occurred at 0.9 M NaCl without added glutamate. Distinct protein bands were produced under stressful conditions, which indicate that these proteins might be stress proteins that aid the isolates to counteract osmotic stress.

Keywords: Osmotic stress, L-Glutamate, Escherichia coli

Location: Department of Microbiology, University of Dhaka

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Performance

Objectives:

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.

Methodology:

The four environmental isolates (E₁, E₂, E₃ and E₄), four clinical isolates (C₁, C₂, C₃and 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 K₂HPO₄, 3.0 g KH₂PO4, 0.1 g Na-citrate.2H2O, 0.1 g Mg SO4. 7H2O, 1.0 g (NH4)₂SO₄ and 900 ml water. Solution B contains 2.0 g glucose and 100 ml water. Stock solution of L-glutamate (solution C) was prepared by mixing 2.205 g of L-glutamate in 20 ml and water. The glutamate solution was freshly prepared and sterilized with syringe filter device of 0.45 μm pore size. In order to impose salt stress, organisms were grown overnight at 37°C in absence and presence of NaCl salt of different molar concentration (0.6, 0.8 and 0.9 M). To counteract the stress, L-glutamate at a concentration of 15 mM was added to each medium. Cell growth was monitored by taking absorbance in a spectrophotometer at 600 nm total viable bacterial count was measured by drop-plate method16. Soluble protein in the culture supernatant was estimated according to the Bradford method17. SDS-PAGE analysis was carried out as described elsewhere.

Source of Information: Bangladesh J Microbiol, Volume 25, Number 1, June 2008, pp 79-81

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

In conclusion, analysis of the protein profile of the test organisms after resolution by SDS-PAGE demonstrated several distinct bands. Distinct protein bands were found for all the E. coli isolates grown at 0.9 M NaCl with 15 mM L-glutamate. These bands were not evident when growth occurred in the presence of the same salt concentration but without L-glutamate. It is suspected that these proteins might be induced by the osmotic stress and were therefore stress proteins. It is also reasonable to assume that L-glutamate aided the organisms to overcome stress induced by NaCl.

Knowledge Management: Journal