title: Importance of branched-chain amino acid utilization in Francisella intracellular adaptation.
abstract: Intracellular bacterial pathogens have adapted their metabolism to optimally utilize the nutrients available in infected host cells. We recently reported the identification of an asparagine transporter required specifically for cytosolic multiplication of Francisella. In the present work, we characterized a new member of the major super family (MSF) of transporters, involved in isoleucine uptake. We show that this transporter (here designated IleP) plays a critical role in intracellular metabolic adaptation of Francisella. Inactivation of IleP severely impaired intracellular F. tularensis subsp. novicida multiplication in all cell types tested and reduced bacterial virulence in the mouse model. To further establish the importance of the ileP gene in F. tularensis pathogenesis, we constructed a chromosomal deletion mutant of ileP (ΔFTL_1803) in the F. tularensis subsp. holarctica live vaccine strain (LVS). Inactivation of IleP in the F. tularensis LVS provoked comparable intracellular growth defects, confirming the critical role of this transporter in isoleucine uptake. The data presented establish, for the first time, the importance of isoleucine utilization for efficient phagosomal escape and cytosolic multiplication of Francisella and suggest that virulent F. tularensis subspecies have lost their branched-chain amino acid biosynthetic pathways and rely exclusively on dedicated uptake systems. This loss of function is likely to reflect an evolution toward a predominantly intracellular life style of the pathogen. Amino acid transporters should be thus considered major players in the adaptation of intracellular pathogens.
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, Paris, France INSERM U1151, CNRS UMR 8253, Institut Necker-Enfants Malades, Equipe 11, Pathogénie des Infections Systémiques, Paris, France.
authors.forename: Gael
authors.initials: G
authors.lastname: Gesbert
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, Paris, France INSERM U1151, CNRS UMR 8253, Institut Necker-Enfants Malades, Equipe 11, Pathogénie des Infections Systémiques, Paris, France.
authors.forename: Elodie
authors.initials: E
authors.lastname: Ramond
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, Paris, France INSERM U1151, CNRS UMR 8253, Institut Necker-Enfants Malades, Equipe 11, Pathogénie des Infections Systémiques, Paris, France.
authors.forename: Fabiola
authors.initials: F
authors.lastname: Tros
authors.affiliation: Equipe RMCX Université Paris Diderot, Sorbonne Paris Cité, Unité de Biologie Fonctionnelle et Adaptative, UMR 8251 CNRS, Paris, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Dairou
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, Paris, France INSERM U1151, CNRS UMR 8253, Institut Necker-Enfants Malades, Equipe 11, Pathogénie des Infections Systémiques, Paris, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Frapy
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, Paris, France INSERM U1151, CNRS UMR 8253, Institut Necker-Enfants Malades, Equipe 11, Pathogénie des Infections Systémiques, Paris, France.
authors.forename: Monique
authors.initials: M
authors.lastname: Barel
authors.affiliation: Université Paris Descartes, Sorbonne Paris Cité, Paris, France INSERM U1151, CNRS UMR 8253, Institut Necker-Enfants Malades, Equipe 11, Pathogénie des Infections Systémiques, Paris, France alain.charbit@inserm.fr.
authors.forename: Alain
authors.initials: A
authors.lastname: Charbit
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003600:Cytosol / Q000382:microbiology; D004195:Disease Models, Animal; D005260:Female; D005604:Francisella tularensis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D017353:Gene Deletion; D007532:Isoleucine / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008807:Mice, Inbred BALB C; D010588:Phagosomes / Q000382:microbiology; D014406:Tularemia / Q000382:microbiology / Q000473:pathology
chemical_list: D026901:Membrane Transport Proteins; D007532:Isoleucine