Effects of environmental stresses on the activities of the uspA, grpE and rpoS promoters of Escherichia coli O157:H7.

Heat shock proteins and RNA polymerase sigma factor play an important role in protecting cells against environmental stresses, including starvation, osmotic and oxidative stresses, and cold shock. In this study, the effect of environmental stresses on activity of the auto-fluorescent Escherichia coli O157:H7 generated by the fusion of gfp(uv) to E. coli uspA, grpE and rpoS promoters were examined. Osmotic shock caused about a 4-fold increase in green fluorescence of E. coli O157:H7 harboring uspA::gfp(uv) or rpoS::gfp(uv) at 37 degrees C and room temperature whereas osmotic shock at 5 degrees C did not induce green fluorescence. When starved, E. coli O157:H7 possessing grpE::gfp(uv) was more sensitive for evaluating stress at low temperature while uspA::gfp(uv) was better suited for detecting the stress response at higher temperature. The uspA, grpE and rpoS promoters were up-regulated to varying degrees by stresses commonly encountered during food processing.