Septin barriers protect mammalian host cells against Pseudomonas aeruginosa invasion

Septin GTPases polymerize into higher-ordered structures as a part of the cytoskeleton and are involved in interactions of the host with a wide spectrum of pathogens. Many pathogens foster an ambiguous relationship with septins. They exploit septins for uptake, but septins also prevent their intracellular replication and target them for autophagy. We demonstrate that septins are involved in a defense mechanism against the pathogen Pseudomonas aeruginosa, which enters cells via a lipid zippering mechanism relying on interaction of the lectin LecA with the glycosphingolipid Gb3 on the host membrane. LecA-dependent invagination of the plasma membrane triggers septin recruitment to the site of bacterial attachment. We also find a septin-dependent reinforcement of cortical actin at attachment sites. Atomic force microscopy reveals formation of a septin-dependent rigid barrier below the membrane, preventing bacterial penetration. Our data suggest that septin barriers represent a cellular defense against bacteria inducing membrane curvature for invasion. [Display omitted] •Host cell attachment of P. aeruginosa triggers localized septin recruitment•Septins form a local barrier by increasing cellular rigidity•Septin recruitment inhibits LecA-dependent bacterial uptake into host cells Septins are involved in host-pathogen interactions. Aigal et al. show that septins are recruited to the attachment site of P. aeruginosa, which utilizes a surface lectin to bind to the host membrane, resulting in attachment, membrane deformation, and entry. Septins can prevent this invasion process by locally increasing membrane rigidity.