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Abstract
s σ, commonly known as RpoS, is a subunit of bacterial RNA polymerase and a general stress regulator which is up-regulated when bacteria are subjected to sub-optimal environmental conditions such as high temperature and high osmolarity. The objective of this study was to investigate the ability of Escherichia coli B23 cells to cross-protect against high osmolarity by first subjecting the cells to high temperature shock then exposing the cells to hyperosmolarity. Cell viability was then measured to estimate overall cell survival. The cells that were dual-treated had a 1.5-fold reduction in cell viability as compared to the cells subjected to only hyperosmolarity. RpoS expression in the different treatments was examined by Western immunoblotting with a monoclonal RpoS-specific antibody. The heat shocked and control cells had approximately equal amounts of RpoS expression. The dual-treated cells had the highest level of RpoS expression, whereas the cells subjected to just hyperosmolarity had the lowest. No cross-protection was observed as cell viability in dual-treated cells was unexpectedly low compared to cells subjected to just hyperosmolarity; a possible explanation is that increased RpoS expression could have increased production of genes responsible for cell death, therefore, sacrificing part of the population to increase nutrients available and to better the chance of survival for the rest of the population. Future experiments including improvements of the experimental procedure, alterations in the order and number of stress – conditions and using RpoS mutant strains may be helpful to better understand the mechanism of RpoS in response to sequential stresses.