A Quorum-Sensing Autoinducer that Controls Bacterial Group Behaviors and a Phage Lysis-Lysogeny Decision

Abstract

Bacterial collective behaviors are regulated by the cell-cell communication process called quorum sensing. Quorum sensing relies on the production, release, and group-wide detection of extracellular signal molecules called autoinducers. Quorum sensing is well established in the Vibrio genus, for which Vibrio cholerae is a particularly compelling model as it causes the globally-important human disease cholera and quorum sensing controls pathogenicity. This thesis describes the discovery of a new quorum-sensing system in V. cholerae and other Vibrios consisting of a receptor-transcription factor called VqmA and an autoinducer called DPO. Upon binding DPO, VqmA activates transcription of a gene encoding a small RNA (sRNA), called VqmR, and VqmR represses genes involved in biofilm formation and virulence factor production. Repression of these traits is crucial for V. cholerae to disperse from its human host and disseminate to new victims. The second part of this thesis describes phage-encoded quorum-sensing-like systems. One such system is employed by the phage VP882, which infects and kills Vibrios including V. cholerae. VP882 encodes a VqmA homolog, which I named VqmAPhage. Analogous to bacterial VqmA, VqmAPhage binds to DPO produced by its host bacterium. However, unlike bacterial quorum sensing, which benefits the bacterial population, activation of the VP882 phage-based quorum-sensing system benefits the phage at the expense of the host bacteria by promoting the spread of the phage infection and bacterial-cell killing. Specifically, in V. cholerae infected with the VP882 quorum-sensing phage, DPO, via VqmAPhage, activates expression of a gene encoding an antirepressor called Qtip, which inactivates the phage master regulator, leading to phage replication and lytic development. Additional chapters of this thesis are devoted to characterizing the mechanism by which the VP882 quorum-sensing pathway functions with a focus on Qtip and the discovery that other phage-based quorum-sensing-like pathways exist. Finally, I used genetic engineering to reprogram phages to be responsive to user-defined cues. These recombinant phages have the potential to be developed into therapies for environmental, industrial, and medical applications.