The type 6 secretion system (T6SS) is a nanomachine used by many
Gram-negative bacteria, including Vibrio cholerae, to deliver toxic
effector proteins into adjacent eukaryotic and bacterial cells. Because
the activity of the T6SS is dependent on direct contact between
cells, its activity is limited to bacteria growing on solid
surfaces or in biofilms. V. cholerae can produce an exopolysaccharide
(EPS) matrix that plays a role in adhesion and biofilm formation.
In this work, we investigated the effect of EPS production on
T6SS activity between cells. We found that EPS produced by V.
cholerae cells functions as a unidirectional protective armor that
blocks exogenous T6SS attacks without interfering with its own
T6SS functionality. This EPS armor is effective against both samespecies
and heterologous attackers. Mutations modulating the
level of EPS biosynthesis gene expression result in corresponding
modulation in V. cholerae resistance to exogenous T6SS attack.
These results provide insight into the potential role of extracellular
biopolymers, including polysaccharides, capsules, and S-layers in
protecting bacterial cells from attacks involving cell-associated
macromolecular protein machines that cannot readily diffuse
through these mechanical defenses
