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Ferrous Iron Sensing and Responding in Pseudomonas aeruginosa


Kreamer, Naomi N. (2015) Ferrous Iron Sensing and Responding in Pseudomonas aeruginosa. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9DN4324.


Controlling iron distribution is important for all organisms, and is key in bacterial pathogenesis. It has long been understood that cystic fibrosis (CF) patient sputum contains elevated iron concentrations. However, anaerobic bacteria have been isolated from CF sputum and hypoxic zones in sputum have been measured. Because ferrous iron [Fe(II)] is stable in reducing, acidic conditions, it could exist in the CF lung. I show that a two-component system, BqsRS, specifically responds to Fe(II) in the CF pathogen, Pseudomonas aeruginosa. Concurrently, a clinical study found that Fe(II) is present in CF sputum at all stages of lung function decline. Fe(II), not Fe(III) correlates with patients in the most severe disease state. Furthermore, transcripts of the newly identified BqsRS were detected in sputum. Two component systems are the main method bacteria interact with their extracellular environment. A typical two-component system contains a sensor histidine kinase, which upon activation phosphorylates a response regulator that then acts as a transcription factor to elicit a cellular response to stimuli. To explore the mechanism of BqsRS, I describe the Fe(II)-sensing RExxE motif in the sensor BqsS and determine the consensus DNA sequence BqsR binds. With the BqsR binding sequence, I identify novel regulon members through bioinformatic and molecular biology techniques. From the predicted function of new BqsR regulon members, I find that Fe(II) elicits a response that globally protects the cells against cationic stressors, including clinically relevant antibiotics. Subsequently, I use BqsR as a case study to determine if promoter outputs can accurately be predicted based only on a deep understanding of a transcriptional activator’s operator or if a broader regulatory context is required for accurate predictions at all genomic loci. This work highlights the importance of Fe(II) as a (micro)environmental factor, even in conditions typically thought of as aerobic. Since the presence of Fe(II) can alter P. aeruginosa’s antibiotic susceptibility, combining the current strategy of targeting Fe(III) with a new approach targeting Fe(II) may help eradicate infections in the CF lung in the future.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Pseudomonas, iron, cystic fibrosis, two-component systems, regulatory networks
Degree Grantor:California Institute of Technology
Division:Biology and Biological Engineering
Major Option:Biochemistry and Molecular Biophysics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Newman, Dianne K.
Thesis Committee:
  • Gray, Harry B. (chair)
  • Rees, Douglas C.
  • Shan, Shu-ou
  • Phillips, Robert B.
  • Newman, Dianne K.
Defense Date:16 March 2015
Additional Information:The Caltech Option "Biochemistry and Molecular Biophysics" is considered an Interdisciplinary Program. The author studied in both the Biology and Biological Engineering (BBE) and the Chemistry and Chemical Engineering (CCE) divisions to earn her degree. She is listed under BBE in the 2015 Commencement program.
Funding AgencyGrant Number
National Science FoundationUNSPECIFIED
National Institutes of Health (NIH)UNSPECIFIED
Record Number:CaltechTHESIS:03092015-135659710
Persistent URL:
Related URLs:
URLURL TypeDescription adapted for ch. 2 adapted for ch. 3
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8777
Deposited By: Naomi Kreamer
Deposited On:06 Oct 2016 16:11
Last Modified:08 Nov 2023 00:46

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