Carbon Catabolite Regulation of Yersinia pestis Pathogenesis

In order to survive in the unique environments associated with different aspects of the infectious cycle, Yersinia pestis evokes adaptive responses to concertedly regulate gene expression. The overall objective of this project was to ascertain the impact of carbon catabolite regulation upon Y. pestis pathogenesis. Specifically, this research encompassed two major aspects: 1) regulation of Y. pestis biofilm formation, a key transmission factor, and 2) characterization of carbon catabolite regulation amid conditions reflective of mammalian infection. Findings demonstrate that Y. pestis biofilm formation is subject to carbon catabolite regulation in which primary carbon sources inhibit biofilm production, and alternate carbon sources induce robust biofilm development. The differential modulation of Y. pestis biofilm production was found to be facilitated by the cAMP receptor protein, CRP. The microevolution of Y. pestis biovar Orientalis is characterized by loss of glycerol fermentation resulting from dysfunction of glpD and ensured by impairment of the glpFKX operon. Through a mode of action presumably independent of CRP regulation, glpD has been shown to promote Y. pestis biofilm production. Findings in this study also clarified conflicting observations made by independent investigative groups, indicating that the Hfq sRNA chaperone differentially modulates Y. pestis biofilm production in response to primary or alternate available carbon sources. The thermo-regulated sRNA species, Ysr172 and sR084, were shown to be dispensable for Y. pestis biofilm production. Contrary to what has been described for E. coli, the carbon storage regulator protein, CsrA, was found to be a positive regulator of Y. pestis biofilm formation. Loss of hmsP, encoding a cyclic diguanylate phosphodiesterase, restored biofilm production in a csrA-deficient mutant, providing insight regarding the mechanism of Y. pestis biofilm regulation. Deletion of csrA severely impaired Y. pestis growth in peptide-rich HIB at 37°C. Furthermore, loss of csrA resulted in a toxic effect at 37°C during growth in chemically defined BCS medium, regardless of available carbon source. Lethality was described for both pCD1 positive and negative Y. pestis strains, thereby refuting a low-calcium response (Lcr). Mutants deficient in csrA had reduced survival upon murine macrophage-like cell challenge, demonstrating CsrA may serve a crucial Y. pestis virulence regulator.