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
Dissertation Director: Dr. Monique van Hoek
Committee members: Dr. Serguei Popov, Dr. Geraldine Grant, Dr. Barney
Title: "Regulation of Francisella novicida Biofilm by LL-37
The dissertation is on reserve in the Johnson Center Library, Fairfax
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
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.