The Hayes lab studies the molecular mechanisms of microbial competition, cooperation and kin selection. Much of this work focuses on the contact-dependent growth inhibition (CDI) systems of Gram-negative bacteria. CDI+ bacteria express cell-surface CdiA effectors that deliver C-terminal toxin domains into neighboring bacteria through a receptor-mediated process. CDI+ cells also produce immunity proteins, which neutralize toxin domains delivered from siblings. Research from the lab has revealed the protein-protein interactions governing target-cell recognition, toxin delivery and immunity. CDI toxin,immunity proteins are diverse and form an elaborate network of specific cognate pairs. During delivery, CDI toxins hijack a variety of integral membrane proteins to translocate into target bacteria. Finally, CdiA proteins recognize self receptors. Receptor specificity limits CDI to closely related bacteria, but also provides a mechanism for cooperative behaviors between isogenic kin cells.