Kathryn M. Ramsey 1 , 2 , Hannah E. Ledvina 3 , Tenayaann M. Tresko 3 , Jamie M. Wandzilak 2 , Catherine A. Tower 3 , Thomas Tallo 1 , Caroline E. Schramm 4 , S. Brook Peterson 3 , Shawn J. Skerrett 4 , Joseph D. Mougous 3 , 5 , * , Simon L. Dove 1 , *
3 June 2020
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.
Prominent amongst the host-derived nutrients Francisella tularensis requires for intracellular growth is glutathione (GSH), a tripeptide which serves as an essential source of cysteine. Here we comprehensively identify those genes F. tularensis requires for intramacrophage growth and characterize two that play previously unrecognized roles in GSH utilization. One of these encodes a transporter of the dipeptide Cys-Gly which is a breakdown product of GSH, while the other encodes a member of the ChaC family of proteins which we show plays a role in GSH breakdown. Our findings uncover a critical role for a member of the proton-dependent oligopeptide transporter family in Francisella intramacrophage growth and provide the first example of a ChaC family enzyme acting to catabolize GSH in bacteria.