The pentose phosphate pathway constitutes a major metabolic hub in pathogenic Francisella

Héloise Rytter,Fabiola Tros,Fabricio Edgar De Moraes,Mathieu Coureuil,Alain Charbit,Nicolas Goudin,Anne Jamet,Carlos Labate,Pauline Lagouge-Roussey,Ida Chiara Guerrera,Ivan Nemazanyy,Daniel Euphrasie,Elodie Ramond,Jason Ziveri,Cerina Chhuon

doi:10.1371/journal.ppat.1009326

Abstract

Metabolic pathways are now considered as intrinsic virulence attributes of pathogenic bacteria and thus represent potential targets for antibacterial strategies. Here we focused on the role of the pentose phosphate pathway (PPP) and its connections with other metabolic pathways in the pathophysiology of Francisella novicida. The involvement of the PPP in the intracellular life cycle of Francisella was first demonstrated by studying PPP inactivating mutants. Indeed, we observed that inactivation of the tktA, rpiA or rpe genes severely impaired intramacrophage multiplication during the first 24 hours. However, time-lapse video microscopy demonstrated that rpiA and rpe mutants were able to resume late intracellular multiplication. To better understand the links between PPP and other metabolic networks in the bacterium, we also performed an extensive proteo-metabolomic analysis of these mutants. We show that the PPP constitutes a major bacterial metabolic hub with multiple connections to glycolysis, the tricarboxylic acid cycle and other pathways, such as fatty acid degradation and sulfur metabolism. Altogether our study highlights how PPP plays a key role in the pathogenesis and growth of Francisella in its intracellular niche.

Highlights

Francisella tularensis is the causative agent of the zoonotic disease tularemia [1]
Metabolic pathways are intimately associated with the virulence of pathogenic bacteria and are interesting antibacterial targets
We focused on the role of the pentose phosphate pathway (PPP) in the intracellular life cycle of the bacterium Francisella novicida

Summary

Introduction

Francisella tularensis is the causative agent of the zoonotic disease tularemia [1]. This facultative intracellular bacterial pathogen is able to infect numerous cell types but is thought to replicate and disseminate mainly in macrophages in vivo [2]. The four major subspecies (subsp) of F. tularensis currently listed are the subsps: tularensis, holarctica, mediasiatica and novicida (the latter is called F. novicida) These subsps differ in their virulence and geographical origin [3] but all cause a fulminant disease in mice that is similar to tularemia in humans [4]. Francisella virulence is tightly linked to its capacity to multiply exclusively in the cytosolic compartment of infected cells, and in particular in macrophages in vivo. We have shown that gluconeogenesis was essential for Francisella intracellular multiplication [9,10], allowing hostderived substrates such as amino acid, pyruvate and glycerol to be used as carbon, nitrogen and energy sources

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