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Abstract
A sudden increase in the osmolarity of the environment is highly detrimental to the growth and survival of Escherichia coli, thus it must promptly sense changes in the external osmolarity and instigate appropriate adaptation responses. To determine how the cell is affected by ionic and non-ionic hyperosmotic stress, lac operon expression was monitored indirectly by measuring the activity of β -galactosidase. The results indicated that the Lac repressor was affected under hyperosmotic conditions. In particular, there was higher β – galactosidase activity under higher osmolarity due to the Lac repressor. Results also revealed that transcription of the lac operon was affected differently under NaCl (ionic) and sucrose (non-ionic) osmotic stress. A 3 fold higher β -galactosidase activity in NaCl osmotically induced cells in contrast to sucrose treatments at 0.6 Osm and 1.2 Osm was observed. The results for NaCl induced osmotic stress correlated with our hypothesis, however the effects on β -galactosidase activity under sucrose induced osmotic stress were contrary to our hypothesis, as the expected up-regulation of the enzyme activity was not observed.