Control of Bacterial Virulence through the Peptide Signature of the Habitat

Emilia Krypotou,Mariela Scortti,Christin Grundström,Melanie Oelker,Ben F Luisi,A Elisabeth Sauer-Eriksson,José Vázquez-Boland

doi:10.1016/j.celrep.2019.01.073

Abstract

SummaryTo optimize fitness, pathogens selectively activate their virulence program upon host entry. Here, we report that the facultative intracellular bacterium Listeria monocytogenes exploits exogenous oligopeptides, a ubiquitous organic N source, to sense the environment and control the activity of its virulence transcriptional activator, PrfA. Using a genetic screen in adsorbent-treated (PrfA-inducing) medium, we found that PrfA is functionally regulated by the balance between activating and inhibitory nutritional peptides scavenged via the Opp transport system. Activating peptides provide essential cysteine precursor for the PrfA-inducing cofactor glutathione (GSH). Non-cysteine-containing peptides cause promiscuous PrfA inhibition. Biophysical and co-crystallization studies reveal that peptides inhibit PrfA through steric blockade of the GSH binding site, a regulation mechanism directly linking bacterial virulence and metabolism. L. monocytogenes mutant analysis in macrophages and our functional data support a model in which changes in the balance of antagonistic Opp-imported oligopeptides promote PrfA induction intracellularly and PrfA repression outside the host.

Highlights

Listeria monocytogenes, the causative agent of foodborne listeriosis, is a paradigmatic example of a pathogen exerting tight control over its virulence genes (Freitag et al, 2009)
We performed a transposon screen to characterize the molecular basis of the intriguing effect of adsorbents on listerial virulence expression. We show that this effect depends on a functional Opp oligopeptide transporter, which allows L. monocytogenes to control PrfA-GSH regulation according to the ‘‘peptide signature’’ of the bacterial habitat
Genetic Screen for Amberlite XAD4 Non-activable Mutants A himar1 transposon (Tn) library was constructed in L. monocytogenes P14-Phly-lux, a wild-type serovar 4b isolate carrying a chromosomally integrated luxABCDE reporter under the control of the PrfA-regulated hly promoter (Bron et al, 2006). ‘‘Non-activable’’ (PrfA–) Tn mutants were selected in Amberlite XAD4-treated brain-heart infusion (BHI) (BHI-Amb) by exploiting the ability of the PrfA-regulated organophosphate permease Hpt to confer susceptibility to the antibiotic fosfomycin (Scortti et al, 2006)

Summary

Introduction

The causative agent of foodborne listeriosis, is a paradigmatic example of a pathogen exerting tight control over its virulence genes (Freitag et al, 2009) This ubiquitous gram-positive bacterium uses a set of nine virulence factors to promote host cell invasion (InlA, InlB), phagosomal escape (hly-encoded LLO, PlcA, and PlcB), rapid cytosolic replication (Hpt), and cell-to-cell spread (ActA, InlC) (Hamon et al, 2006). PrfA regulation operates through control of (1) PrfA abundance, exerted at both the transcriptional and translational levels and involving positive autoregulation of the prfA gene, and (2) PrfA activity, via cofactor-mediated allosteric shift between low- (‘‘Off’’) and high- (‘‘On’’) activity states (reviewed in Scortti et al [2007]) The latter is thought to play a key role in the strong PrfA induction observed during intracellular infection (Deshayes et al, 2012). While GSH is required for full PrfA induction and intracellular proliferation (Gopal et al, 2005; Reniere et al, 2015), how GSHdependent PrfA activity is regulated remains to be clarified

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