MECHANISMS OF PBGA INVOLVEMENT IN SALMONELLA TYPHIMURIUM LIPID HOMEOSTASIS FOR BACTERIAL PATHOGENESIS

PROJECT SUMMARY/ABSTRACT Salmonella enterica serovar Typhimurium (STm) cause bacteremia in immunocompromised humans bysurviving within the vacuoles of macrophages (M?s). Treatment demands antibiotics that can penetrate to thevacuolar salmonellae and fluoroquinolones are currently preferred. Consequently, resistant STm isolates haveemerged and new therapies are necessary. Like for most Gram-negative bacteria, Enterobacteriaceae producean outer-membrane (OM) lipid bilayer that forms a barrier to the environment and protects against antibiotickilling and host-immune responses. STm regulate the glycerophospholipid (GPL) and the lipopolysaccharide(LPS) molecules within their asymmetric surface bilayer to enhance the barrier and promote survival in M?sduring bacteremia. However, the exact bacterial lipid-remodeling proteins and mechanisms necessary duringinfection are largely unknown. We showed that STm rely upon a conserved enterobacterial transmembrane protein, PbgA, to maintainOM-lipid homeostasis for barrier function and survival in M?s during bacteremia in mice. PbgA bindstetraacylated cardiolipin (CL)-GPL molecules and directs their trafficking to the OM in response to host cues.The data support that STm adapted PbgA to promote LPS stability and OM homeostasis for survival withinhost vacuoles. We hypothesize that salmonellae exploit structural features and binding interactions ofPbgA to control OM-lipid homeostasis during bacteremia. We will pursue this central inquiry by addressingthe following specific aims: 1) Define the functional contribution of PbgA-periplasmic domain (PD)subregions and residues for OM-CL trafficking. 2) Define PbgA interactions within the STm envelopenecessary for lipid homeostasis and pathogenesis. 3) Delineate the role of PbgA and CL in STm-LPShomeostasis during bacteremia. Minimal knowledge exists for how enteric bacteria transport GPL to the OM. To the best of ourknowledge, PbgA is one of the first examples of a protein involved in direct physical translocation of CLmolecules across the dual-membrane cell envelope of a Gram-negative bacterium. In understanding PbgA inSTm, we hope to inform common mechanisms of OM-lipid trafficking used by enteric pathogens to adapt andsurvive within the mammalian host environment.