The response to stationary‐phase stress conditions in Escherichia coli : role and regulation of the glutamic acid decarboxylase system

Abstract

SummaryInducible bacterial amino acid decarboxylases are expressed at the end of active cell division to counteract acidification of the extracellular environment during fermentative growth. It has been proposed that acid resistance in some enteric bacteria strictly relies on a glutamic acid-dependent system. The Escherichia coli chromosome contains distinct genes encoding two biochemically identical isoforms of glutamic acid decarboxylase, GadA and GadB. The gadC gene, located downstream of gadB, has been proposed to encode a putative antiporter implicated in the export of ␥-aminobutyrate, the glutamic acid decarboxylation product. In the present work, we provide in vivo evidence that gadC is co-transcribed with gadB and that the functional glutamic acid-dependent system requires the activities of both GadA/B and GadC. We also found that expression of gad genes is positively regulated by acidic shock, salt stress and stationary growth phase. Mutations in hns, the gene for the histone-like protein H-NS, cause derepressed expression of the gad genes, whereas the rpoS mutation abrogates gad transcription even in the hns background. According to our results, the master regulators H-NS and RpoS are hierarchically involved in the transcriptional control of gad expression: H-NS prevents gad expression during the exponential growth whereas the alternative sigma factor RpoS relieves H-NS repression during the stationary phase, directly or indirectly accounting for transcription of gad genes.

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

“…Highlighting the importance of the AR2 system is the plethora of regulators involved in its regulation, the relative importance of each regulator depending on environmental pH and growth phase. These regulators include: two phosphorelays, EvgAS (Masuda & Church, 2002) and TorRS (Bordi et al, 2003), the stationary phase s s -factor (De Biase et al, 1999), the global regulators Crp ) and H-NS (Hommais et al, 2001), three AraC-like regulators, GadW (Ma et al, 2002), GadX (Shin et al, 2001) and YdeO (Masuda & Church, 2003), and the Era-like GTPase TrmE (Gong et al, 2004). Central to the AR2 system is the activity of the LuxRlike transcription regulator GadE, as most of the regulators listed target gadE expression.…”

Polyamines and Glutamate Decarboxylase-based Acid Resistance in Escherichia coli

“…The glutamate decarboxylase (GAD, 1 EC 4.1.1.15) system has been extensively studied because of its major role in the acid resistance of enteric pathogens such as E. coli O157, Shigella flexneri, and Listeria monocytogenes (6,7,8,29). E. coli contains two genes, gadA and gadB (mapped at 78 and 33 min on its chromosome), which encode two biochemically indistinguishable forms of GAD and are very similar in sequence (2,9,24).…”

“…E. coli contains two genes, gadA and gadB (mapped at 78 and 33 min on its chromosome), which encode two biochemically indistinguishable forms of GAD and are very similar in sequence (2,9,24). Sequential reaction through GAD and the putative glutamate/GABA antiporter encoded by the gadC gene allows cells to remove intracellular protons (8).…”

Role of the AraC–XylS family regulator YdeO in multi-drug resistance of Escherichia coli

“…32,33 One of the most efficient acid resistance systems in E. coli, the Gad system, is based on the coordinated action of two isoforms of glutamate decarboxylase (GadA and GadB) and of a specific glutamate/g-aminobutyrate (GABA) antiporter (GadC). 34,35 The gadA/BC genes, activated in response to acid stress, are subject to complex circuits of regulation involving the AraC-XylS family regulator YdeO. 36 In this study, we demonstrate that YdeO contributes to the multi-drug resistance as well as the acid resistance of E. coli.…”

“…One very efficient E. coli acid resistance system encompasses two isoforms of glutamate decarboxylase (gadA and gadB) and a putative glutamate/GABA antiporter (gadC). 34,35 It is subject to complex controls that vary with growth medium, growth phase and growth pH. Earlier work has revealed that this system is also controlled by YdeO (Figure 4).…”