Oral Presentation BacPath 2024

FhaB and FhaC from Bordetella function as a two-partner toxin delivery system (#21)

Richard M Johnson 1 , Peggy A Cotter 1 , Zachary M Nash 1
  1. University of North Carolina at Chapel Hill, Chapel Hill, NORTH CAROLINA, United States

Bacteria rely on surface proteins to interact with solid surfaces, other microorganisms, and,  importantly for pathogens, eukaryotic hosts. Gram-negative bacteria, which have complex diderm  cell envelopes, have evolved specialized secretion systems to export proteins from the cytoplasm  to the cell surface. My research focuses on understanding molecular mechanisms underlying the  broadly distributed Two Partner Secretion (TPS or Type Vb) pathway, which includes many  important virulence factors and interbacterial contact-dependent inhibition systems.  

TPS systems consist of an Omp85 TpsB transporter that transports a large TpsA exoprotein  across the Gram-negative outer membrane. The best studied TPS system is FhaB/FhaC, produced by Bordetella species such as B. pertussis, which causes whooping cough in humans,  and B. bronchiseptica, which causes respiratory disease in a wide range of mammals. The TpsA  protein FhaB mediates adherence to host cells, suppresses the initial inflammatory response, and  is required for resistance to killing by phagocytic cells by an unknown mechanism. Examination  of the FhaB secretion pathway, its topology on the bacterial surface, and interactions between  FhaB and another virulence factor –Bordetella’s adenylyl cyclase toxin (ACT)– have led us to  hypothesize that FhaB and FhaC protect the bacteria from phagocytes by acting as a toxin  delivery system. 

Here, we investigated key aspects of this model. We performed Western blots on WCLs and  supernatants collected from wildtype (WT) B. bronchiseptica and mutant strains lacking ACT  (∆cyaA) and determined that the loss of ACT is correlated with increased degradation of FhaB,  indicating that ACT binding stabilizes FhaB on the bacterial surface. We developed a surface-bound toxin delivery assay by decorating FhaB on recipient ∆cyaA bacteria (that cannot produce  their own ACT) with ACT from donor cells and used cyclic-AMP ELISAs to determine that the  FhaB-bound toxin is delivered to eukaryotic cells in vitro.

  1. Nash ZM, Inatsuka CS, Cotter PA, Johnson RM.2024.Bordetella filamentous hemagglutinin and adenylate cyclase toxin interactions on the bacterial surface are consistent with FhaB-mediated delivery of ACT to phagocytic cells. mBio15:e00632-24.https://doi.org/10.1128/mbio.00632-24
  2. Johnson RM, Nash ZM, Dedloff MR, Shook JC, Cotter PA.2021.DegP Initiates Regulated Processing of Filamentous Hemagglutinin in Bordetella bronchiseptica. mBio12:10.1128/mbio.01465-21.https://doi.org/10.1128/mbio.01465-21