Polyamines are critical for the induction of the glutamate decarboxylase-dependent acid resistance system in Escherichia coli

As part of our studies on the biological functions of polyamines we have used a mutant of Escherichia coli that lacks all the genes for polyamine biosynthesis for a global transcription analysis on the effect of added polyamines. The most striking early response to polyamine addition is the increased expression of the genes for the glutamate dependent acid resistance system (GDAR) that is essential for the survival of bacteria when passing through the acid environment of the stomach. Not only were the two genes for glutamate decarboxylases (gadA and gadB) and the gene for glutamate --aminobutyrate antiporter (gadC) induced by polyamine addition, but also the various genes involved in the regulation of this system were induced. We confirmed the importance of polyamines for the induction of the GDAR system by direct measurement of glutamate decarboxylase activity and acid-survival. Effects of deletions of the regulatory genes in the GDAR system and on the effects of overproduction of two of these genes were also studied. Strikingly, overproductions of the alternate sigma factor rpoS and of the regulatory gene gadE resulted in very high levels of glutamate decarboxylase and almost complete protection against acid stress even in the absence of any polyamines. Thus, these data show that a major function of polyamines in E. coli is protection against acid stress by increasing the synthesis of glutamate decarboxylase, presumably by increasing the levels of the rpoS and gadE regulators.

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Chattopadhyay MK, Tabor H