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Open Access Dissertation
Doctor of Philosophy (PhD)
Year Degree Awarded
Month Degree Awarded
Virtually all living organisms are capable of sensing individuals within a population and communicating amongst themselves to coordinate group behavior. This group coordination holds true for all living organisms, from multi-cellular organisms like humans down to the single-celled microbes including bacteria. In order to survive in everchanging environments, bacteria have developed strategies to determine their current surroundings and communicate with individuals in the population to respond to environmental changes. Bacteria have many different forms of communication similar to the many different human languages. These signals are used to coordinate a variety of biological processes in a density-dependent manner in a process referred to as quorum sensing.
Chapter 1 provides an introduction into the mechanisms used by bacteria to regulate quorum sensing including different regulatory strategies, use of cell-cell signaling molecules by gram-positive and gram-negative bacteria, and strategies to disrupt the quorum response in a process called quorum quenching. A heavy emphasis is placed on the molecular mechanisms used by Bacillus subtilis to regulate a variety of biological processes during the quorum response.
Chapter 2 focuses on a detailed study to dissect the molecular mechanisms Rap regulatory proteins use to modulate the activity of the transcriptional activator ComA. Using genetic approaches, we identified additional Rap regulatory proteins that regulate ComA and identified the distinct surfaces on ComA that Class I and Class II Rap regulatory proteins use to modulate ComA activity. From this work, we were able to classify Rap regulatory proteins into Class I, Class II, and Class III anti-activators of ComA.
Chapter 3 describes work to identify additional quorum sensing pathways that function independently of ComA. To begin to identify these molecules, conditioned media was generated and added back to low-cell density cultures and the changes in gene transcription were analyzed. We identified a novel iron acquisition activity present in conditioned media made from domesticated wild type B. subtilis. This iron acquisition activity is outcompeted by bacillibactin and enterobactin, two siderophores produced by undomesticated B. subtilis and E. coli, respectively. Finally, we identify the highly conserved EfeUOB pathway as required for uptake of this iron acquisition activity.
Roy, Emily, "Dissecting regulatory mechanisms of ComA-dependent and ComA-independent quorum sensing pathways in Bacillus subtilis" (2018). Doctoral Dissertations. 1386.