Polyamines Are Critical for the Induction of the Glutamate Decarboxylase-dependent Acid Resistance System in Escherichia coli

Manas K Chattopadhyay,Herbert Tabor

doi:10.1074/jbc.m113.510552

Abstract

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 transcriptional analysis on the effect of added polyamines. The most striking early response to the polyamine addition is the increased expression of the genes for the glutamate-dependent acid resistance system (GDAR) that is important for the survival of the 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-γ-aminobutyrate antiporter (gadC) induced by the polyamine addition, but the various genes involved in the regulation of this system were also induced. We confirmed the importance of polyamines for the induction of the GDAR system by direct measurement of glutamate decarboxylase activity and acid survival. The effect of deletions of the regulatory genes on the GDAR system and the effects of overproduction of two of these genes were also studied. Strikingly, overproduction of the alternative σ 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.

Highlights

Global Gene Expression in Response to Polyamine Supplementation to a Polyamine Mutant of E. coli: Polyamines Induce Genes Involved in the Acid Response Pathway—For these studies we used the E. coli mutant, as we described previously [28], that has deletions in all nine of the genes involved in polyamine biosynthesis and modified as described under “Experimental Procedures” to have a wild type sequence in the rpoS gene
The entire data set for the microarray study on the effect of polyamine addition has been deposited with a GEO accession number GSE49918
Despite the fact that polyamines have been reported to have many physiological functions [2, 3, 5, 47,48,49,50], it is noteworthy that even though the addition of polyamines to our polyamine mutant of E. coli resulted in change in expression of many genes, the most striking changes in gene transcription in our Glutamate decarboxylase was measured in the cell extracts in triplicate

Summary

Background

Results: Polyamines induce various components of the glutamate-dependent acid resistance pathway (GDAR) in Escherichia coli and are important for protection against acid stress. The most striking early response to the polyamine addition is the increased expression of the genes for the glutamate-dependent acid resistance system (GDAR) that is important for the survival of the bacteria when passing through the acid environment of the stomach. Overproduction of the alternative ␴ 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. We found that five of the seven genes that showed the largest induction soon after polyamine addition are involved in the E. coli acid response system; three are involved in the glutamate decarboxylase-dependent acid resistance (GDAR) system. Because RpoS is known to be important in various stress response systems, we have converted the rpoS amber mutation in our strain to rpoS (wild type) for use in the current experiments

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION