GadE (YhiE) activates glutamate decarboxylase‐dependent acid resistance in Escherichia coli K‐12

Abstract

SummaryCommensal and pathogenic strains of Escherichia coli possess three inducible acid resistance systems that collaboratively protect cells against acid stress to pH 2 or below. The most effective system requires glutamate in the acid challenge media and relies on two glutamate decarboxylases (GadA and B) combined with a putative glutamate: g g g g -aminobutyric acid antiporter (GadC). A complex network of regulators mediates induction of this system in response to various media, pH and growth phase signals. We report that the LuxR-like regulator GadE (formerly YhiE) is required for expression of gadA and gadBC regardless of media or growth conditions. This protein binds directly to the 20 bp GAD box sequence found in the control regions of both loci. Two previously identified AraC-like regulators, GadX and GadW, are only needed for gadA/BC expression under some circumstances. Overexpression of GadX or GadW will not overcome a need for GadE. However, overexpression of GadE can supplant a requirement for GadX and W. Data provided also indicate that GadX and GadE can simultaneously bind the area around the GAD box region and probably form a complex. The gadA , gadBC and gadE genes are all induced by low pH in exponential phase cells grown in minimal glucose media. The acid induction of gadA/BC results primarily from the acid induction of gadE . Constitutive expression of GadE removes most pH control over the glutamate decarboxylase and antiporter genes. The small amount of remaining pH control is governed by GadX and W. The finding that gadE mutations also diminish the effectiveness of the other two acid resistance systems suggests that GadE influences the expression of additional acid resistance components. The number of regulatory proteins (five), sigma factors (two) and regulatory feedback loops focused on gadA/BC expression make this one of the most intensively regulated systems in E. coli .

Molecular Mechanism of Transcriptional Cascade Initiated by the EvgS/EvgA System inEscherichia coliK-12

“…2C lane 6), indicating that their expression was GadE dependent. We have also confirmed by DNase I footprinting analysis that GadE directly bound to the GAD boxes 19,20) in the promoter regions of these genes (Figs. 5 and 6).…”

Indole induces the expression of multidrug exporter genes in Escherichia coli

“…Indole-induced expression of mdtEF requires the gadX gene, which encodes an AraC-type transcription factor. GadX is known to induce various genes including gadA, hdeAB and yhiE under low pH conditions (Masuda and Church, 2003;Ma et al, 2003). However, as indole obviously does not cause acidification of the medium, our results indicate that GadX responds to indole even under non-acidic conditions.…”

The glutamate-dependent acid resistance system in Escherichia coli: essential and dual role of the His–Asp phosphorelay RcsCDB/AF

“…Acid resistance is correlated with the ability of both regulators to activate the expression of the gadA and gadBC operons during the stationary phase of growth. The activation of gadA/B expression by GadE requires a GadE-binding box upstream of the promoter Ma et al, 2003). Deletion and mutation analyses of gadA/BC regulatory regions did not reveal a motif that would specifically affect RcsB-dependent activation without affecting that of GadE.…”

“…3(a). The gadA, gadB, gadX and gadE fusions were described by and Ma et al (2002Ma et al ( , 2003; the limits for gadA and gadB are shown in Fig. 3(a).…”