The Escherichia coli AraC-family regulators GadX and GadW activate gadE, the central activator of glutamate-dependent acid resistance

Abstract

Escherichia coli can survive pH 2 acid stress by using several acid resistance systems. The most efficient of these employs glutamate decarboxylase (GadA/GadB) to consume protons, and an antiporter (GadC) to exchange the intracellular decarboxylation product for external glutamic acid. Expression of the essential transcriptional activator of this system, GadE, is controlled by several regulators in a hierarchical fashion. In this study, two additional activators have been identified. The AraC-family regulators GadX and GadW, previously found to activate gadA/BC in vitro, are now shown in vivo to directly activate gadE expression, which, in turn, activates the gadA/BC genes. In vivo results using E. coli and Salmonella enterica show that these regulators actually have little direct effect on gadA and gadBC promoters. The numerous gadE induction pathways converge on a 798 bp control region situated upstream of the gadE promoter region. Deletions of this control region exposed the region between "798 and "360 nt (relative to the translational start) to be required for maximum gadE-lacZ expression in Luria-Bertani (LB) medium and to be the primary focus of GadX and GadW control. The GadE protein itself, which binds to three GAD box sequences present between "233 and "42 nt, helped activate GadE expression in LB, but only when the "798 to "360 region was absent. These regulatory regions and proteins appear to integrate a variety of physiological signals that forecast a need for GadE-dependent gene expression and acid resistance.

Characterization of Glutamate Decarboxylase from a High γ-Aminobutyric Acid (GABA)-Producer,Lactobacillus paracasei

“…In LAB and E. coli, GABA production is among the most important mechanisms for achieving acid resistance. [26][27][28] Since Lb. paracasei increases acidity via growth, it has been suggested that it produces GABA in order to increase the pH of the growth medium.…”

OmpR positively regulates urease expression to enhance acid survival of Yersinia pseudotuberculosis

“…In addition, many other genes which express metabolic enzymes, periplasmic proteins and regulators involved in AR in E. coli have also been examined by microarray and proteomic 2D-gel analyses (Blankenhorn et al, 1999;Tucker et al, 2002). Recently, the Lon protease, endoRNase RNase E and chaperone Hsp31 have been shown to be important in controlling AR systems in E. coli (Heuveling et al, 2008;Mujacic & Baneyx, 2007;Takada et al, 2007), and the roles of AraC-family regulators GadX and GadW and the multidrug resistance regulator MarA in AR systems have also been investigated (Ruiz et al, 2008;Sayed et al, 2007;Tramonti et al, 2006). Nevertheless, despite advances in unravelling some of the regulatory networks involved in AR systems (Foster, 2004;Masuda & Church, 2003), it remains unclear how these factors function together to promote cell survival in low pH conditions.…”

Global Regulator of Virulence A (GrvA) Coordinates Expression of Discrete Pathogenic Mechanisms in Enterohemorrhagic Escherichia coli through Interactions with GadW-GadE

“…4A) (55). Promoter activity from fragments containing the P1 or P3 promoter alone (Frag-2 and Frag-4, respectively) was also significantly higher in TW14359 ⌬grvA (P Ͻ 0.05), while activity from the fragment containing only the P2 promoter (Frag-3) did not differ between TW14359 ⌬grvA and TW14359.…”

“…This is supported by both gadE-lacZ promoter fusions and RNA-seq analysis in this study. GadW is an AraC-family regulator that acts as a homodimer or, when partnered with GadX, to control the acid fitness genes gadBC, hdeA, hdeB, and gadE (54,55,77,78). The details of how GrvA regulates transcription are not yet known.…”

“…GrvA regulates the expression of Ͼ700 genes in EHEC O157:H7 strain TW14359. The model is inferred from the results of experiments performed in this and previous studies (20,21,52,53,55). See the text for further details.…”