Polyamines Stimulate the Level of the σ38 Subunit (RpoS) of Escherichia coli RNA Polymerase, Resulting in the Induction of the Glutamate Decarboxylase-dependent Acid Response System via the gadE Regulon

Manas K Chattopadhyay,Chithra N Keembiyehetty,Weiping Chen,Herbert Tabor

doi:10.1074/jbc.m115.655688

Abstract

To study the physiological roles of polyamines, we carried out a global microarray analysis on the effect of adding polyamines to an Escherichia coli mutant that lacks polyamines because of deletions in the genes in the polyamine biosynthetic pathway. Previously, we have reported that the earliest response to polyamine addition is the increased expression of the genes for the glutamate-dependent acid resistance system (GDAR). We also presented preliminary evidence for the involvement of rpoS and gadE regulators. In the current study, further confirmation of the regulatory roles of rpoS and gadE is shown by a comparison of genome-wide expression profiling data from a series of microarrays comparing the genes induced by polyamine addition to polyamine-free rpoS(+)/gadE(+) cells with genes induced by polyamine addition to polyamine-free ΔrpoS/gadE(+) and rpoS(+)/ΔgadE cells. The results indicate that most of the genes in the E. coli GDAR system that are induced by polyamines require rpoS and gadE. Our data also show that gadE is the main regulator of GDAR and other acid fitness island genes. Both polyamines and rpoS are necessary for the expression of gadE gene from the three promoters of gadE (P1, P2, and P3). The most important effect of polyamine addition is the very rapid increase in the level of RpoS sigma factor. Our current hypothesis is that polyamines increase the level of RpoS protein and that this increased RpoS level is responsible for the stimulation of gadE expression, which in turn induces the GDAR system in E. coli.

Highlights

Polyamines are ubiquitous compounds present in most organisms
Our results indicate that polyamines do not directly increase the synthesis of the glutamate decarboxylase enzymes; instead, the increase in the RpoS protein stimulates the synthesis of the GadE regulatory protein and other components of the glutamate decarboxylase acid resistance system
The induction of the glutamate-dependent-acid resistance (GDAR) system is of particular importance because it is necessary for the survival of various pathogenic and nonpathogenic bacteria when exposed to the acids present in the stomach [14]

Summary

Background

Polyamines are ubiquitous compounds present in most organisms. Results: Polyamines increase the level of RpoS, the ␴38-RNA-polymerase subunit, even in non-amber-strain, to induce glutamate-dependent-acid resistance (GDAR) in Escherichia coli via gadE. We presented preliminary evidence that two regulatory factors rpoS and gadE are important for this induction by polyamines of the glutamate-dependent-acid resistance system It was not clear how these genes were involved in the polyamine induction of the GDAR system. We postulate a cascade model in which the primary action of the polyamine addition to the polyamine-deficient cells is the very rapid increase in the RpoS level with subsequent induction of gadE expression that in turn increases the GDAR system This demonstration of the effect of polyamines in rapidly increasing the RpoS level is of importance for understanding the requirement of polyamines for the glutamate-dependent acid response system and for the likely role of the polyamines in regulating the large number of systems already known to involve RpoS and to be induced by various stress conditions

Experimental Procedures

Results

Discussion