| As a model microorganism, Escherichia coli has been widely used. Osmotic conditions usually exist in most industrial bioprocesses, which might affect the growth of strains and the yield of products. This study focuses on the physiological and metabolic responses of E. coli mutants deficient in osmotic stress-related genes on several osmotic conditions.In the first part of study, physiological responses of eleven E. coli mutants (△.ennvZ, AompR, AompF, AompC, AompA, AompT, AosmE,△osmB, AosmC, AosmY, AompW) were studied under different salt stresses. The growth of almost all strains were repressed when salt was introduced into the medium. Results included that the osmE gene significantly affects the strain growth under0.2M NaCl. The effects of this gene were, however, not that significant when NaCl concentration increased to0.4M. Under higher salt condition, the OmpW protein was found to repress the growth of cells.Next, the effects of four genes (envZ, ompR, ompF, ompC) involved in the EnvZ/OmpR two-component system were emphasized. Results indicated that the ompR gene significantly enhances the cell growth and resists the salt stress based on the studies of cell physiology, activity of major metabolic enzymes, and intracellular metabolic reaction fluxes. Insignificant effects on cell growth were observed for the other three genes in the EnvZ/OmpR system under both normal and salt stress conditions.The effects of above four genes in the metabolism of carbohydrate were also investigated. Glucose is an important nutrient source, which provides necessary carbon and energy for cell growth. With the increase in glucose concentration in the medium, all four genes exhibited the enhancement of cell growth rate as well as the resistance to glucose stress by repressing the formation of acetate. The outer membrane protein OmpC was found sensitive to glucose stress and showed to be more important than the outer membrane protein of OmpF. |
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