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Dissertation Defense Announcement
To:  The George Mason University Community

Candidate: Saira Ahmad Chaudry
Program:    PhD Biosciences

Date:   Monday April 23, 2012
Time:   3:30 p.m.
Place:   George Mason University
             Occoquan Bldg., Room 204
             Prince William campus
 
Dissertation Director: Dr. Monique van Hoek
Committee members: Dr. Serguei Popov, Dr. Geraldine Grant, Dr. Barney Bishop,

Title: "Regulation of Francisella novicida Biofilm by LL-37 Peptide"


The dissertation is on reserve in the Johnson Center Library, Fairfax campus.
The doctoral project will not be read at the meeting, but should be read in advance.

All members of the George Mason University community are invited to attend.


ABSTRACT:
Biofilms are a natural aggregation of bacterial colonies surrounded by an extracellular polymeric matrix that protects the bacteria from antibiotic treatments and increases survival compared to planktonic bacteria. LL-37 peptide is a human cathelicidin peptide that exhibits antimicrobial activity including anti-biofilm activity in gram-negative and gram-positive bacteria.  Francisella species are Category A, gram-negative, facultative intracellular pathogens resulting in the disease of tularemia with as little as 10 bacteria present. Francisella has recently shown to form biofilms in vitro.
LL-37 peptide exerts anti-biofilm activity against F. novicida at low concentrations of 0.24 µg/ml, but its bacterial targets are not known.  The goal of this research is to identify the unique molecular targets of the LL-37 peptide in F. novicida, which may lead to a better understanding of the mechanism of action of LL-37 against many bacteria.
Confocal images of F. novicida incubated with 0.24 g/ml LL-37 peptide for increasing hours have shown a decrease in depth and tightness of biofilm formation compared untreated F. novicida biofilm. LL-37 peptide, at the aforementioned concentration, also inhibited F. novicida initial attachment, which is the first step of biofilm formation. The enantiomer, D-LL-37 peptide, also exerted anti-biofilm activity against F. novicida.  While the region of anti-biofilm activity of the peptide varies depending on the bacterial species, residues 18-37 of LL-37 peptide have been determined as the region of anti-biofilm activity in F. novicida.
LL-37 peptide has been shown to affect many biofilm-associated genes in F. novicida.  These include pil assembly proteins, LPS-assembly proteins, efflux systems, transferases, and pyruvate synthetase for metabolism.  Indeed mutations of these genes have resulted in altered biofilm formation.  LL-37 also down regulates expression of response regulators kdpE, while up-regulating expression of response regulator qseB.  Expression of kdpE normally negatively affects expression of qseB.  qseB regulates activation of transcription of many genes that may be involved in regulating biofilm formation.  Indeed, many of these qseB-regulated genes (such as acetlytransferase, major facilitator superfamily (MFS) transporter protein, pyruvate, and hypothetical membrane proteins) have been shown to be associated with biofilm formation. Identifying the targets of LL-37 peptide in F. novicida has helped to understand how the peptide functions in the bacteria to exert its anti-biofilm effects.

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