Streptococcus suis exports WapA polymorphic toxins to compete with tonsil microbiota for an optimal colonization

Background: Streptococcus suis is a zoonotic pathogen, and its colonization of the host tonsil is believed to be a vital source causing Infection, while its mechanism competing for a stable tonsil niche is unknown. Rearrangement hotspot (Rhs) proteins are characterized to facilitate interbacterial competition by their polymorphic C-terminal toxins (CTs) in diverse bacteria, while their distant homologues emerged in S. suis, referred to as wall-associated protein A (WapA), has not been identified.

Methods: Bioinformatics, western blot and interbacterial competition analyses were performed to identify Rhs/WapA toxins and their roles during S. suis Infection.

Results: The 350 kDa WapA-CT1, linked with a SecF-like protein and a SrtB sortase, was verified to manipulate the tonsil microbiota for S. suis optimal colonization. The unfolded WapA-CT1 was translocated across the cell membrane via the canonical Sec pathway. Afterward, autocleavage generated four fragments: the N-terminal NCWB fragment, two middle Rhs domains (Rhs1&2) that may fold as a β-barrel structure, and a C-terminal PreT-CT toxin domain. SrtB interacts with the NCWB region, and plays vital roles for the interbacterial antagonism mediated by the toxic CT1.

Conclusion: This discovery underscores the diversity of mechanisms by which pathogens delivering Rhs/WapA polymorphic toxins, and their roles in competing with the host microbiota.