COMBATING OF ESCHERICHIA COLI STRAINS AGAINST SALINITY BY THE ANTIOXIDANT DEFENSE SYSTEM AND OSMOREGULATION: BIOCHEMICAL AND PHYSIOLOGICAL APPROACHES

The study was designed to elucidate the impacts of salinity on biochemical and physiological properties of two Escherichia coli strains (6E and S39) isolated from different sites. The strains were exposed to 600 and 1200 mM NaCl and were harvested after 12th and 24th h of incubation. The lipid peroxidation levels, osmolyte accumulation, H2O2 content and antioxidant system [superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), ascorbate peroxidase (APX) and glutathione reductase(GR)] of the bacteria were investigated. While thiobarbituric acid reactive substances (TBARS) and H2O2 content of S39 has increased steadily with salinity, however, it has not changed at 600 mM NaCl concentration in strain 6E. Accumulation of the osmolytes in 6E increased depending on salinity and application time. In S39 except for glycine-betaine, contents of other osmolytes were either unchanged or decreased. Activities of SOD, CAT, POX, APX, GR and NOX have increased as compared to the control group in 6E exposed to 600 and 1200 mM salt for 12h. In S39, CAT, POX, and GR activities decreased exposed to salinity. Consequently, it can be argued that (i) the different antioxidant responses of 6E in salinity plays a key role which tend to make 6E the more tolerant (ii) this tolerance is closely related to the increased antioxidant capacity against reactive oxygen species and is related to the increased accumulation of osmolytes.