Putrescine as a modulator of the level of RNA polymerase sigma S subunit in Escherichia coli cells under acid stress.

Metabolites accumulated in the culture medium of Escherichia coli cells induce expression of the rpoS gene encoding the alternative sigmaS subunit of RNA polymerase, which controls adaptation of E. coli to acid stress during growth in glucose-mineral medium. The effect of acetate and succinate as end products of E. coli metabolism has been investigated on the levels of transcription, translation, and sigmaS protein stability. These end products mainly influenced the stability of the RNA polymerase sigmaS subunit. Under conditions of acid stress caused by acetate addition, the content of polyamines in the cells and medium decreased, whereas artificial rpoS gene switch-off by antisense RNA was accompanied by increase in polyamine level. Addition of polyamine to E. coli cells treated with acetate and especially with succinate caused a significant concentration-dependent stimulatory effect on rpoS expression. Thus, induction of the rpoS regulon depends on the combined action of the investigated metabolites determining adequate control of gene expression under conditions of acid stress. A scheme for metabolic pathways describing the role of putrescine in the maintenance of intracellular pH and polyamine pool homeostasis during E. coli adaptation to acid stress is proposed.