Structure and Function of Burkholderia Contact-Dependent Growth Inhibition (CDI) Systems

Social interactions between bacteria impact infectious disease transmission and progression. The molecular mechanisms underlying bacteria-bacteria competition and communication also represent a largely unexplored set of therapeutic targets that could be manipulated to treat or prevent infections. Contact-dependent growth inhibition (CDI) is a phenomenon in which Gram-negative bacteria deliver the toxic C-terminus of a large, polymorphic surface protein (BcpA) to the cytoplasm of neighboring bacteria upon direct cell-cell contact, inhibiting the growth of the targeted recipient cell unless it produces an appropriate immunity protein (BcpI). While CDI systems have been investigated almost exclusively for their ability to mediate interbacterial competition, our previous work indicated that CDI systems also facilitate interbacterial communication by inducing specific gene expression and phenotypic changes in immune recipient bacteria (those producing the appropriate immunity protein, BcpI). Thus, CDI systems enable bacterial self/nonself discrimination through several overlapping mechanisms, all of which could be exploited therapeutically. However, fundamental gaps in our knowledge of CDI system molecular function prevent a clear understanding of how these proteins impact bacterial sociality and limit the development of CDI system-based antimicrobials, decontaminants, or vaccines. Thus, our long term goal is to identify the molecular mechanisms underlying CDI system function toward manipulating these proteins for the treatment or prevention of infectious disease. Our preliminary data show that Burkholderia species provide a tractable model system for interrogating CDI system biology. This proposal seeks to understand how BcpA is delivered from one bacterium to another and how this process shapes bacterial behavior. Toward these goals, the proposal tests the hypothesis that Burkholderia-specific membrane and periplasmic factors facilitate BcpA exchange between bacterial neighbors, resulting in discrete roles for surface-localized (on donor bacteria) and exchanged (delivered to recipient cells) BcpA. The proposed model will be tested by (1) identifying the recipient cell surface and cytoplasmic membrane receptor(s) for BcpA; (2) defining donor cell secreted proteins and BcpA subdomains responsible for maintaining appropriate delivery to recipients; and (3) delineating the role on donor cells for accessory protein BcpO in BcpA function. Together, this research program will provide critical insight into a specific mechanism of b