Effect of Changing Osmotic Stress on lac Operon Expression in Escherichia coli K-12 Wild Type Strain B23

Previous studies have focused primarily on the effects of changing hyperosmotic stress on the expression of particular sigma factors, and stress regulons in Escherichia coli. Prior experiments have shown that stress regulons play a prominent role in transcriptional regulation of various cellular osmoprotectants, and other genes involved in the osmotic stress response. This experiment was conducted in order to test whether the expression of the lac operon in E. coli is under the direct influence of hyperosmotic stress. E. coli B23 cells were exposed to various environmental concentrations of sodium chloride and the activity of the lac operon was monitored by assaying β -galactosidase production. Two separate trials were conducted in order to investigate the effect of different stages of cell growth on the expression of the lac operon in a hyperosmotic environment. The results indicated that there was an exponential decrease in β -galactosidase production in with increasing osmolarity in stationary phase cells, implying that the lac operon is repressed under such conditions. The cells in exponential phase of growth were also affected by varying external osmolarity; however, the pattern of β -galactosidase production differed remarkably from that observed by stationary cells, which was likely a result of prior exposure of the cells to high temperatures. In essence, the lac operon is amongst many genes affected by osmotic stress; however, additional factors, including the stage of growth and environmental stresses, such as increased temperature, may influence transcription of the lac operon.