Pseudomonas aeruginosa type III-secreted toxin ExoT inhibits host-cell division by targeting cytokinesis at multiple steps.

Pseudomonas aeruginosa is an opportunistic pathogen that requires preexisiting epithelial injury to cause acute infections. We report that P. aeruginosa inhibits mammalian cytokinesis in a type III secretion system and exotoxin T (ExoT)-dependent manner. ExoT is a bifunctional type III secretion system effector protein that contains an N-terminal GTPase-activating protein domain and a C-terminal ADP-ribosyl transferase domain. Each of its domains inhibits cytokinesis in a kinetically, morphologically, and mechanistically distinct manner. The GTPase-activating protein-mediated inhibition of cytokinesis occurs early, likely as a consequence of its inhibitory effect on RhoA. The ADP-ribosyl transferase domain inhibits late steps of cytokinesis by blocking syntaxin-2 localization to the midbody, an event essential for completion of cytokinesis. These findings provide an example of a bacterial pathogen targeting cytokinesis.