Hyperosmotic shock induces the σ 32 and σ E stress regulons of Escherichia coli

The rise in the levels of σ S that accompanies hyperosmotic shock plays an important role in Escherichia coli survival by increasing the transcription of genes involved in the synthesis and transport of osmoprotectants. To determine if other stress regulons collaborate with σ S in dealing with high osmolality, we used single copy fusions of lacZ to representative promoters induced by protein misfolding in the cytoplasm ( dnaK and ibp  ), extracytoplasmic stress [P3 rpoH and htrA ( degP  )] and cold shock ( cspA ). Both the σ 32 ‐dependent, dnaK and ibp , promoters, and the σ E ‐dependent, P3 rpoH and htrA , promoters were rapidly but transiently induced when mid‐exponential phase cells were treated with 0.464 M sucrose. The cspA promoter, however, did not respond to the same treatment. Overproduction of the cytoplasmic domain of the σ E anti‐sigma factor, RseA, reduced the magnitude of osmotic induction in λφ(P3 rpoH::lacZ  ) lysogens, but had no effect on the activation of the dnaK and ibp promoters. Similarly, induction of the dnaK::lacZ and ibp::lacZ fusions was not altered in either rpoS or ompR genetic backgrounds. Osmotic upshift led to a twofold increase in the enzymatic activity of the λTLF247 rpoH::lacZ translational fusion whether or not the cells were treated with rifampicin, indicating that both heat shock and exposure to high osmolality trigger a transient increase in rpoH translation. Our results suggest that the σ 32 , σ E and σ S regulons closely co‐operate in the managment of hyperosmotic stress. Induction of the σ 32 and σ E regulons appears to be an emergency response required to repair protein misfolding and facilitate the proper folding of proteins that are rapidly synthesized following loss of turgor, while providing a mechanism to increase the activity of σ S , the primary stress factor in osmoadaptation.