Date of Degree
MS (Master of Science)
Timothy L. Yahr
First Committee Member
Craig D Ellermeier
Second Committee Member
Linda L McCarter
Pseudomonas aeruginosa is a gram-negative pathogen that causes opportunistic infections in immunocompromised individuals. Whereas clinical isolates from acute infections are characterized by host cell cytotoxicity and motility, isolates from chronic infections are characterized by biofilm formation and persistence. The type III secretion system (T3SS) causes cytotoxicity by injecting effectors into host cells. T3SS gene expression is activated by ExsA, an AraC family transcriptional regulator. Transcription of exsA is controlled by two promoters, PexsC and PexsA, which are regulated by ExsA and the cAMP-Vfr system, respectively. Additional global regulatory systems also influence T3SS including the second messenger signaling molecule c-di-GMP and the RsmAYZ regulatory system. c-di-GMP signaling increases biofilm production and decreases acute virulence factor expression. A previous study found that c-di-GMP alters cAMP levels and affect cAMP-Vfr signaling. Other studies found that c-di-GMP signaling alters expression of the small non-coding regulatory RNAs, rsmY and rsmZ. The RsmAYZ post-transcriptional regulatory system regulates ExsA translation. We hypothesize that c-di-GMP regulates T3SS expression by altering exsA transcription through the cAMP-Vfr dependent PexsA promoter. Overexpression of YfiN, a c-di-GMP synthase, decreases T3SS reporter activity in PA103 and requires a functional GGDEF active site for full inhibition. Inhibition by YfiN does not require rsmYZ. YfiN expression decreases cAMP-Vfr signaling and coordinately inhibits PexsA-lacZ reporter activity. Consistent with the proposed model, YfiN expression in a vfr mutant does not further decrease T3SS reporter activity. These data indicate that the YfiN alters T3SS expression through transcriptional control of the cAMP-Vfr dependent PexsA promoter.
Pseudomonas aeruginosa is a widely dispersed environmental bacterium that is a prominent cause of opportunistic infections in hospitals. P. aeruginosa infections cause severe disease that can spread rapidly throughout the body and result in death within days or weeks. In the context of cystic fibrosis, P. aeruginosa can chronically infect an individual for years and decades. Chronic infections are a significant source of morbidity and difficult to treat with antibiotics. Cystic fibrosis patients are genetically susceptible to developing chronic lung infections and often succumb to complications arising from P. aeruginosa infection. P. aeruginosa produces a type III secretion system (T3SS) that contributes significantly to morbidity and mortality during acute infections. As the infection becomes chronic, expression of the T3SS decreases. P. aeruginosa produces cyclic-di-GMP, which is a signaling molecule that in the context of infection, determines the phenotype (i.e., acute vs. chronic infection). As cyclic-di-GMP levels increase, the infection phenotype becomes more chronic. Cyclic-di-GMP also regulates T3SS expression. As cyclic-di-GMP levels increase, T3SS expression decreases. How cyclic-di-GMP regulates the T3SS remains to be thoroughly investigated. This study focuses on identifying and determining the relative importance of pathways that mediate cyclic-di-GMP inhibition of the T3SS. Understanding cyclic-di-GMP signaling regulation of T3SS expression, and the transition from acute infection to chronic infection will help develop and inform therapeutic approaches for treatment of P. aeruginosa infections.
cAMP-Vfr, cyclic-di-GMP, ExsA, Pseudomonas aeruginosa, RsmAYZ, type III secretion system
viii, 64 pages
Includes bibliographical references (pages 53-64).
Copyright © 2017 Adam Bailin
Bailin, Adam. "Regulation of the Pseudomonas aeruginosa type III secretion system by cyclic-di-GMP." MS (Master of Science) thesis, University of Iowa, 2017.