Tn-Seq reveals hidden complexity in the utilization of host-derived glutathione in Francisella tularensis

• Published in: PLoS pathogens Vol. 16; no. 6; p. e1008566
• Main Authors: Ramsey, Kathryn M, Ledvina, Hannah E, Tresko, Tenayaann M, Wandzilak, Jamie M, Tower, Catherine A, Tallo, Thomas, Schramm, Caroline E, Peterson, S Brook, Skerrett, Shawn J, Mougous, Joseph D, Dove, Simon L
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01-06-2020; Public Library of Science (PLoS)
• Subjects: Animals; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biology and Life Sciences; Breakdown; Cell Line; Critical care; Cysteine; Cytoplasm; Dipeptides - genetics; Dipeptides - metabolism; Enzymes; Female; Francisella tularensis; Francisella tularensis - physiology; Funding; Genes; Genomes; Glutathione; Glutathione - genetics; Glutathione - metabolism; Hospitals; Host-Pathogen Interactions - physiology; Infectious diseases; Intracellular; Macrophages; Macrophages - metabolism; Macrophages - microbiology; Macrophages - pathology; Medicine; Medicine and Health Sciences; Metabolism; Mice; Molecular biology; Pathogens; Pharmaceutical sciences; Physical Sciences; Proteins; Research and Analysis Methods; Supervision; Transglutaminases - genetics; Transglutaminases - metabolism; Tularemia - genetics; Tularemia - metabolism; Utilization; Vaccines; Virulence; Rhode Island; United States > US; Massachusetts
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1008566

Host-derived glutathione (GSH) is an essential source of cysteine for the intracellular pathogen Francisella tularensis. In a comprehensive transposon insertion sequencing screen, we identified several F. tularensis genes that play central and previously unappreciated roles in the utilization of GSH during the growth of the bacterium in macrophages. We show that one of these, a gene we named dptA, encodes a proton-dependent oligopeptide transporter that enables growth of the organism on the dipeptide Cys-Gly, a key breakdown product of GSH generated by the enzyme γ-glutamyltranspeptidase (GGT). Although GGT was thought to be the principal enzyme involved in GSH breakdown in F. tularensis, our screen identified a second enzyme, referred to as ChaC, that is also involved in the utilization of exogenous GSH. However, unlike GGT and DptA, we show that the importance of ChaC in supporting intramacrophage growth extends beyond cysteine acquisition. Taken together, our findings provide a compendium of F. tularensis genes required for intracellular growth and identify new players in the metabolism of GSH that could be attractive targets for therapeutic intervention.