I-023. Characterization of the Universal Stress Protein A Paralog uspE of Escherichia coli: Survival and Stress Response

A. F. Glick, A. C. Vollmer;
Swarthmore College, Swarthmore, PA.

Background: The uspA gene in Escherichia coli is involved in many different stress responses, although its exact function is unknown. Studying uspE, a uspA paralog, may provide more information about uspA. The purpose of this study was to characterize the stress response and viability of strains lacking the uspA and uspE genes in the MG1655 and MC4100 backgrounds. Methods: Wild type and mutant strains were tested for survival. Strains were placed in conditions of high levels of hydrogen peroxide (0.05%), ethanol (20%), UV irradiation (550 mJ/cm2), and NaCl (1M), and viability was compared to that of non-stressed cells. Strains transformed with plasmids containing stress promoter::luxCDABE fusions were exposed to sub-lethal levels of stress, and the amount of light produced was measured using a luminometer in order to determine the kinetics of stress response on the transcriptional level. In the case of oxidative stress, the katG promoter was used. Results: In general, the host MC4100 strain was less viable than the comparable MG1655 strain when exposed to high levels of ethanol and peroxide. MC4100 strains display a higher level of variability for various stress responses measured luminometrically. In the MG1655 background, both log and stationary phase ΔuspA and ΔuspE responses to several stressors were measured and compared to wild type. To UV irradiation, both mutants were less viable, regardless of growth phase. While the stationary phase viability in peroxide was decreased for both mutants, there was a differential in survival to this stressor in log phase. Osmotic stress tolerance also was diminished in log phase. Transcriptional activation of katG was higher for the ΔuspA mutant compared to wild type, while it was lower in the ΔuspE mutant. Conclusions: The MC4100 strain is a problematic background for studying stress response as results obtained with this strain are often variable and viability is low compared to MG1655. The uspE gene appears to have a different role than uspA in the survival and stress response of logarithmic and stationary phase cells.