Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Veterinary Microbiology and Preventive Medicine

First Advisor

Frank C. Minion


The etiologic agent of bubonic plague, Yersinia pestis, produces cell density-dependent chemical signals in a process named quorum sensing (QS). Though the closely related enteric pathogen Yersinia pseudotuberculosis uses a QS system to regulate motility, the role of quorum sensing in Y. pestis is unclear. Yersinia pestis possess two conserved QS systems, an AI-1 system that utilizes acyl homoserine lactones (AHLs) as signals and the LuxS pathway that responds to the AI-2 autoinducer. Yersinia pestis has two functional AI-1 pathways, Ysp and Ype. The AI-2 quorum sensing system has been linked to diverse phenotypes and regulatory changes in pathogenic bacteria. For several reasons, it was not clear what effect AHL and AI-2 pathways have on virulence gene expression and survival in the two different hosts, flea and human. Seventeen transcriptional profiling experiments were performed using Y. pestis strain CO92 deltapgm and microarrays based on the same strain. These studies included QS mutant comparison and purified QS signal addition experiments at two temperatures (30yC and 37yC) representing the two hosts. Our microarray studies data were confirmed by qRT-PCR. Statistical analyses were used to determine p, q (false discovery rate) and fold change values as measures of significant transcriptional differences, and thus the identification of Y. pestis quorum sensing regulated functions. Our data show that AHL based signaling can have profound effects on the cellular physiology of Y. pestis, especially on its carbohydrate metabolism and on virulence gene expression at 30yC. Maltose fermentation and the glyoxylate bypass were also induced by AHL signaling in a temperature dependent fashion. Also, AHL quorum sensing systems regulated more genes at the lower temperature suggesting that their impact on flea survival is greater than on virulence in the mammalian host. When strains with single mutations in ypeIR and yspI were examined by transcriptional analysis, deltaypeI controlled more genes although it is responsible for producing only one of the four AHLs, N-(3-oxooctanoyl)-homoserine lactone. In contrast to AHL effects, our data show that AI-2 quorum sensing is associated with metabolic activities and oxidative stress genes that help Y. pestis survive at the host temperature of 37yC.


Copyright Owner

Jing Yu



Date Available


File Format


File Size

118 pages