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I am a Harvard University undergraduate Biochemical Sciences major. I
will be
conducting my honors thesis studies in the Higgins lab. The overall
goal of my project is to identify and characterize bacterial factors
that contribute to the ability of Listeria
monocytogenes to spread from one host cell to another without
encountering the extracellular environment.
I will initially characterize a
previously isolated mutant of L.
monocytogenes. This mutant, SP2T, was created by random
transposon mutagenesis and isolated following infection of murine bone
marrow-derived macrophages using a FACS-based screening procedure
developed in the lab. SP2T has been found to form smaller than normal
plaques during in vitro
infection of mouse L2 fibroblasts, thus indicating a defect in
cell-to-cell spread. We have determined that the mutation in SP2T is
linked to the transposon insertion at the interface of two
uncharacterized genes. I plan to first determine which gene is
responsible for this defect and then determine the cause of the small
plaque
phenotype.
In addition to characterizing the
previously identified SP2T mutant, I will conduct a more thorough
mutagenesis screen to isolate additional spreading mutants. The
original mutagenesis screen was limited in its scope. Furthermore, the
methods used for isolation of mutants have been vastly improved. Given
that the original mutagenesis screen was not saturating, there is
reason to believe that a more rigorous screening approach will produce
novel mutants that have not yet been isolated. These mutants will then
be characterized further for their role in cell-to-cell spread.
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