Autotransporters, the largest family of secreted proteins in Gram-negative bacteria, perform a variety of functions, including adherence, cytotoxicity and immune evasion. InYersinia pestisthe autotransporter YapE has adhesive properties and contributes to disease in the mouse model of bubonic plague. Here, we demonstrate that omptin cleavage ofY. pestisYapE is required to mediate bacterial aggregation and adherence to eukaryotic cells. We demonstrate that omptin cleavage is specific for theY. pestisandY. pseudotuberculosisYapE orthologues but is not conserved in theYersinia enterocoliticaprotein. We also show that cleavage of YapE occurs inY. pestisbut not in the entericYersiniaspecies, and requires the omptin Pla (plasminogen activator protease), which is encoded on theY. pestis-specific plasmid pPCP1. Together, these data show that post-translation modification of YapE appears to be specific toY. pestis, was acquired along with the acquisition of pPCP1 during the divergence ofY. pestisfromY. pseudotuberculosis, and are the first evidence of a novel mechanism to regulate bacterial adherence.