Heat Induced RpoS Expression May Inhibit RpoD-dependent Expression of β-galactosidase in Escherichia coli B23

Abstract

RpoS is a sigma factor in Escherichia coli that is expressed under environmental stress and binds to RNA polymerase to initiate transcription of stress-related genes. Induction of RpoS by one environmental stressor can provide cross protection to other stressors such as antibiotics. Another sigma factor, RpoD, is the primary sigma factor in Escherichia coli responsible for the expression of house-keeping genes including lac Z. Heat shock of Escherichia coli was previously demonstrated to increase RpoS concentrations and induce cross protection to tetracycline, but this induced resistance decreased significantly after prolonged exposure. This study examined whether high levels of RpoS induced by prolonged heat shock inhibits RpoD-dependent gene expression and causes – decreased resistance to tetracycline. Wild type Escherichia coli and RpoS strains were heat shocked and used to perform a minimum inhibitory concentration assay with tetracycline. Presence of RpoD and RpoS in heat shock lysates was detected using enzyme-linked immunosorbent assays. RpoD activity was indirectly measured using a β- galactosidase assay. In the wild type strain, the initial increase in tetracycline resistance was lost after prolonged o incubation at 45 C while RpoS concentrations steadily increased relative to RpoD.  -galactosidase activity in the – wild type strain was significantly lower than the RpoS strain. Our data suggest that increased RpoS expression levels may inhibit RpoD-dependent expression of  -galactosidase.