[SCAN] Bacterial strategies to groom a concealed armour

Scan Seminar

Title: Bacterial strategies to groom a concealed armour

Speaker: Sérgio Filipe

From: Bacterial Cell Surfaces and Pathogenesis Lab, ITQB
 

Abstract:

The ability of the immune system to react against invading bacteria is essential for survival of all organisms. For that purpose, higher organisms, from plants to animals, have specific receptors that recognize Pathogen-Associated Molecular Patterns (PAMP), to initiate a cascade of events that eliminates the bacterial invader.

Peptidoglycan (PGN) is considered a bona fide PAMP. It is the principal constituent of most bacterial cell surfaces and forms a load-bearing protective mesh. Despite being a surface component, PGN is concealed by an outer membrane, in  Gram-negative bacteria, or by layers of glycopolymers and proteins, in Gram-positive bacteria.

We have been interested in determining how Gram-positive PGN is concealed at the bacterial surface. We have shown that the absence of wall teichoic acids (WTA), or the absence of major autolysins, results in increased binding of a PGN perception systems directly to the bacterial surface and in the activation of the host defenses.

While WTA may sterically impair PGN receptors from binding their substrate at the surface of bacterial, PGN hydrolase activity of autolysins seem capable of trimming the outermost PGN fragments at the surface of Gram-positive bacteria to prevent bacterial exposure to the host innate immune system. Therefore, in the absence of autolysins, bacterial virulence is impaired, as PGRPs can directly recognize leftover PGN extending beyond the external layers of bacterial proteins and polysaccharides.

We are currently enquiring which PGN hydrolases contribute to the grooming of the bacterial cell surface and how this process takes place.