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Title: Regulation of transcription of the Escherichia coli Group 2 capsule gene clusters
Author: Aal Owaif, Hasan
ISNI:       0000 0004 6351 6354
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2017
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Capsular polysaccharides are expressed by many bacteria and in the case of pathogens are believed to act as essential virulence factors conferring resistance to host defenses. Escherichia coli strains that express Group 2 capsules are associated with a number of infections including urinary tract infections, and life-threatening infections such as neonatal meningitis and septicemia. The expression of Group 2 capsular polysaccharide is controlled by two temperature regulated promoters PR1 and PR3 that allow the transcription at 37°C but not at 20°C. The 5' untranslated regions of these promoters are involved in the regulation of transcription by interacting with global regulators. In this study, PR1-lacZ and PR3-lacZ transcriptional fusions and transposon mutagenesis was used to identify new regulators of Group 2 E. coli capsule expression. The cAMP-CRP complex was identified to be a new transcriptional regulator of E. coli Group 2 capsular polysaccharide expression. Deletion of cyaAor crp gene led to significant decrease in the transcriptional activity of PR1 and PR3. It was found that PR1 activity is affected by different carbon sources, glucose reduces the transcriptional activity of PR1, while the addition of glycerol increases PR1 activity. The results showed that the cAMP-CRP complex indirectly activates the transcription at PR1 while it directly upregulates the transcription from PR3 by binding to the CRP binding site at +240 bp relative to the transcription start site. Site-directed mutagenesis of the CRP binding site abolished the binding capability of CRP and led to significant decrease in the transcription from PR3. This regulation of transcription at both PR1 and PR3 promoters by the cAMP-CRP complex is growth phase dependent, the transcription from both promoters at mid-log phase is not affected by CRP but at late exponential or stationary phase CRP is required for maximal transcription from these promoters. In addition, this study demonstrated that the transcription from the promoter on the antisense strand of kpsF, occurring mainly at stationary phase, is not regulated by RpoS and does not regulate the transcription from PR1. In conclusion, this study identified a new regulator of E. coli Group 2 capsule gene expression and added more to the current model of the complex regulation of E. coli capsular polysaccharide expression. By understanding capsule expression, it is hoped to detect therapeutic targets in pathogenic E. coli to block capsular polysaccharide expression in the future.
Supervisor: Roberts, Ian Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available