The broadly conserved regulator PhoP links pathogen virulence and membrane potential in Escherichia coli

Abstract

Summary PhoP is considered a virulence regulator despite being conserved in both pathogenic and non-pathogenic Enterobacteriaceae. While Escherichia coli strains represent non-pathogenic commensal isolates and numerous virulent pathotypes, the PhoP virulence regulator has only been studied in commensal E. coli. To better understand how conserved transcription factors contribute to virulence, we characterized PhoP in pathogenic E. coli. Deletion of phoP significantly attenuated E. coli during extraintestinal infection. This was not surprising since we demonstrated that PhoP differentially regulated the transcription of >600 genes. In addition to survival at acidic pH and resistance to polymyxin, PhoP was required for repression of motility and oxygen-independent changes in the expression of primary dehydrogenase and terminal reductase respiratory chain components. All phenotypes have in common a reliance on an energized membrane. Thus, we hypothesized that PhoP mediates these effects by regulating genes encoding proteins that generate proton motive force. Indeed, bacteria lacking PhoP exhibited a hyper-polarized membrane and dissipation of the transmembrane electrochemical gradient increased susceptibility of the phoP mutant to acidic pH, while inhibiting respiratory generation of the proton gradient restored resistance to antimicrobial peptides independent of lipopolysaccharide modification. These findings demonstrate a connection between PhoP, virulence, and the energized state of the membrane.

Bacterial Mg2+Homeostasis, Transport, and Virulence

“…Recent findings present an explanation for this paradoxical energy requirement. As discussed below, the Mg 2+ -responsive PhoP/PhoQ regulatory system, which drives transcription of the mgtA and mgtB genes, also promotes a reversal in membrane potential (i.e., making it positive inside and negative outside of the cytoplasmic membrane) (1). This means that the MgtA and MgtB proteins are made and operate under conditions in which both the chemical and electrical gradients are unfavorable for Mg 2+ movement through a channel, thereby providing a rationale for why ATP hydrolysis is needed to bring Mg 2+ into the cytoplasm.…”

Decreased Expression of Type 1 Fimbriae by apstMutant of Uropathogenic Escherichia coli Reduces Urinary Tract Infection

“…TCSs are composed of an inner-membrane histidine kinase sensor protein and cytoplasmic response regulator (81). TCSs are important for bacterial adaptation and virulence (6,12), and a number of TCSs have been identified to be important for pathogenic E. coli, e.g., BarA-UvrY, PhoPQ, and QseBC (4,31,41,56).…”

Flagella-independent surface motility in Salmonella enterica serovar Typhimurium

“…1A), presumably because the PhoP/PhoQ system is not active in high Mg 2+ (11). The identified motility does not appear to be swarming motility because the PhoP/PhoQ system represses flagella-mediated motility (9,10), and one would expect a phoP mutant to move more than the wild-type strain. In addition, swarming motility requires glucose, and the media had glycerol as the carbon source.…”

“…This is because, first, low Mg 2+ activates the PhoP/ PhoQ system, which hinders flagella-mediated motility by repressing transcription of flagellin (9) and by decreasing membrane potential, which hinders flagellar rotation (10). And second, pagM transcription requires the Mg 2+ transporter MgtA and the F 1 F o ATPase inhibitor MgtC.…”

“…For example, the nature of the carbon source is critical because the cAMP-receptor protein promotes transcription of the flagellar master regulator flhDC operon (7), and the RNA binding regulator CsrA furthers stability of the flhDC mRNA (8). By contrast, the PhoP/PhoQ regulatory system down-regulates flagella-mediated motility by repressing transcription of flagellar genes (9) and by decreasing the membrane potential (10).…”