The Pentose Phosphate Pathway in pathogenic Francisella

Metabolic pathways are now considered as intrinsic virulence attributes of pathogenic bacteria and hence represent potential targets for anti-bacterial strategies. Here, we addressed the role of the pentose phosphate pathway (PPP) and its connections with other metabolic pathways in the pathophysiology of Francisella novicida. We have previously shown that this intracellular bacterial pathogen used gluconeogenesis to metabolize host-derived nutrients in the cytosolic compartment of infected macrophages. Francisella species, which lacks the oxidative branch of the PPP, are equipped with all the genes of the non-oxidative branch (i.e. tktA, tal, rpiA and rpe, encoding transketolase, transaldolase, ribose-phosphate isomerase and ribulose phosphate epimerase, respectively). The involvement of the PPP in the early stage of intracellular life cycle of F. novicida was first demonstrated with the study of PPP inactivation mutants. Indeed, inactivation of tktA, rpiA or rpe genes, severely impaired intramacrophagic multiplication during the first 24–hours. However, time-lapse video microscopy demonstrated that rpiA and rpe mutants were able to resume late intracellular bacterial multiplication. To get further insight into the links between the PPP and other metabolic networks of the bacterium, we next performed a thorough proteo-metabolomic analysis of these mutants. We show that the PPP constitutes a major bacterial metabolic hub with multiple connections with glycolysis, tricarboxylic acid cycle and other metabolic pathways, such as fatty acid degradation and sulfur metabolism. Hence, our study highlights how, by its multiple connections with other metabolic pathways, PPP is instrumental to Francisella pathogenesis and growth in its intracellular niche.