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Abstract
RpoS, a sigma subunit of RNA polymerase in Escherichia coli, is seen as the master regulator of the general stress response which is triggered by stress signals such as high temperature, hyperosmolarity, and low acidic pH, allowing the bacteria to up-regulate the expression of specific proteins that confer resistance against the particular stress environments. The objective of this study was to investigate if cross-protection exists when Escherichia coli B23 was first subjected to high temperature shock followed by hyperosmolarity shock or low acidic pH shock. Various techniques, including OD measurement of cultures at 660nm, cell viability assay, Bradford assay, and Western immunoblotting with monoclonal RpoS-specific antibody were used to assess protection and the expression levels of RpoS in sequential exposure to different stress signals. Cell viability assays showed that when cells were grown at 37 ° C throughout the experiment, cell viability did not vary much whether shocked with high salts or not and the data results suggested no significant cross-protection was observed in dual-treated cells with high temperature (at 42 ° C) followed by sequential hyperosmolarity. The assay also illustrated that when cells were exposed to low pH media without initial incubation at higher temperature (42 ° C) condition, cell viability decreased dramatically, which suggested a possible cross-protection effect in cells treated with high temperature followed by sequential low acidic pH. These results suggested that heat shock at 42 ° C can confer protectivity against low pH but not high osmolarity.