Discovery of a glutathione utilization pathway in Francisella that shows functional divergence between environmental and pathogenic species.

Glutathione (GSH) is an abundant metabolite within eukaryotic cells that can act as a signal, a nutrient source, or serve in a redox capacity for intracellular bacterial pathogens. For Francisella , GSH is thought to be a critical in vivo source of cysteine; however, the cellular pathways permitting GSH utilization by Francisella differ between strains and have remained poorly understood. Using genetic screening, we discovered a unique pathway for GSH utilization in Francisella. Whereas prior work suggested GSH catabolism initiates in the periplasm, the pathway we define consists of a major facilitator superfamily (MFS) member that transports intact GSH and a previously unrecognized bacterial cytoplasmic enzyme that catalyzes the first step of GSH degradation. Interestingly, we find that the transporter gene for this pathway is pseudogenized in pathogenic Francisella , explaining phenotypic discrepancies in GSH utilization among Francisella spp. and revealing a critical role for GSH in the environmental niche of these bacteria. [Display omitted] • Tn-seq identifies a previously unrecognized GSH utilization pathway in F. novicida • A major facilitator transporter pseudogenized in pathogenic Francisella imports GSH • Francisella uses a glutamine amidotransferase to degrade cytoplasmic GSH • A single porin mediates the bulk of outer membrane GSH transport in Francisella Host glutathione (GSH) is a source of cysteine during intracellular replication of Francisella. Wang et al. find Francisella imports GSH via a previously unknown transporter and discover a cytoplasmic GSH-degrading enzyme. This pathway is functional in non-pathogenic Francisella but pseudogenized in pathogenic lineages, suggesting its importance in an environmental niche. [ABSTRACT FROM AUTHOR]