Activation of Escherichia coli's stationary phase gene rpoS

The rpoS gene encodes a stationary phase specific sigma factor of RNA polymerase and is a key regulator of Escherichia coli's stationary phase responses. It has been observed under laboratory conditions that gene expression is induced by stressful environmental conditions and certain metabolic intermediates. Batch and continuous cultures were employed to investigate the effect of environmental conditions and high reactor acetate levels on the transcriptional activation of the rpoS promotor. In complex media, the rpoS gene was induced in the late exponential phase of batch growth. Chemostat experiments were then conducted in complex media to examine the effects of acetate, glucose, and variations in cell density due to media quality on gene expression. Residula acetate and glucose concentrations were found to modulate rpoS behavior. However, it was observed that under these particular experimental conditions, cell density had no appreciable effect on the transcriptional activation of the rpoS promotor