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Laura Case
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E-mail: case0149@umn.edu
Thesis advisor: Gary
Dunny
Year entered: 2006
Degrees received:
B.S., Microbiology, University of Minnesota, Minneapolis,
MN 2005
B.A., English, University of Minnesota, Minneapolis, MN 2005
Honors and Awards:
- MICaB Travel Award Fall 2008
Thesis research:
Conjugal transfer of plasmid pCF10 in Enterococcus
faecalis is induced by the chromosomally encoded peptide
pheromone cCF10. PrgX, a pCF10-encoded protein acts as the
molecular switch controlling the prgQ operon leading
to conjugation. Pheromone binding to PrgX changes its oligomerization
state and abolishes PrgX-mediated repression. Although the
regulation of this system has been studied extensively using
molecular techniques such as lacZ reporter gene fusions
and gene knockout strains, the dynamics of conjugation has
not been studied on a single cell level. To analyze the population
dynamics of pheromone signaling using flow cytometric techniques,
,a translational fusion of the gfp gene downstream
of the pheromone-inducible prgB gene was created.
PrgB is also known as Aggregation substance and acts to clump
cells together to allow for efficient conjugation. Using this
construct, planktonic cell populations were induced to various
levels and examined via flow cytometry to measure the induction
state of the cells. When examined in this manner, planktonic
populations appeared as single peaks with the population average
becoming more induced in a monostable manner. When cells are
grown in a biofilm, they appear to be regulated in an alternate
way. Induction of cells in a biofilm or recently dispersed
from a biofilm demonstrate a population bifurcation following
induction. A small portion of the cells becomes induced at
low levels and increasing inducer concentration leads to a
higher proportion of cells which are turned “on”.
The difference between the regulation of planktonic cells
and biofilm cells is striking. Dispersed biofilm cells also
split into two populations following induction but the cells
are induced at significantly lower levels of cCF10 inducer.
This indicates that the matrix plays a role in slowing the
spread of phereomone throughout the biofilm. Because dispersed
biofilm cells are also regulated in a bistable way, it can
be assumed that although the biofilm matrix plays some role
in conjugation, probably by slowing signal transmission, but
is not responsible for the difference in conjugative regulation.
This data indicates that the cellular changes that occur when
a biofilm is formed may alter the regulation of conjugation.
This could have a significant impact on the transfer of genetic
materials during biofilm formation and persistence.
Publications
- Schlievert, P.M., L.C. Case, K. A. Nemeth, C.C. Davis,
Y. Sun, W. Qin, F.
Wang, A. J. Brosnahan, J.A. Mleziva, M.L. Peterson, and
B.E. Jones. 2007. Alpha
and beta chains of hemoglobin inhibit production of Staphylococcus
aureus
exotoxins. Biochemistry.
2007 Dec 18;46(50):14349-14358.
- Pragman AA, Herron-Olson L, Case LC, Vetter SM, Henke
EE, Kapur V, Schlievert PM. 2007. Sequence analysis of the
Staphylococcus aureus srrAB loci reveals that truncation
of srrA affects growth and virulence factor expression.
J
Bacteriol.189(20):7515-9.
- Schlievert, P.M. and L.C. Case. 2007. Molecular analysis
of staphylococcal
superantigens. Book Chapter. Methods in Molecular Biology:
MRSA Protocols.
Humana Press Inc. 2007. Also in: Methods
Mol Biol. 391:113-26.
- Schlievert, P.M., L.C. Case, K.A. Nemeth, C.C. Davis,
Y. Sun, W. Qin, F. Wang, A.J. Brosnahan, Mleziva, J.A.,
M.L. Peterson, and B.E. Jones. 2007. The alpha and beta
chains of Hemoglobin Inhibit production of Staphylococcus
aureus Exotoxins. Biochemistry
18;46(50):14349-14358.
- Schlievert, P.M., L.C. Case, K.L. Strandberg, Novartis,
and D.Y. Leung. 2008. Superantigen Profile of Staphylococcus
aureus Isolates from Patients with Steroid-Resistant Atopic
Dermatitis. Clin
Infect Dis. 46(9): 1562-1567.
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