Katie Ballering

E-mail: balle028@umn.edu

Thesis Advisor: Gary Dunny

Year entered: 2004

Degrees received:
B.S., Bacteriology, University of Wisconsin-Madison, 2004

Honors and Awards:

• MPGI travel grant (2006)

• MICaB travel grant (2007)

• ASM General Meeting travel grant (2007)

• Student Representative (2007-8)

• Dennis W. Watson Fellowship (2007-08)

• Student representative to the University of Minnesota Board of Regents Equity, Access and Diversity committee (2006-2010)

Thesis research:
Enterococcus faecalis is one of the top three nosocomial pathogens in the US and is a major vector for dissemination of antibiotic resistance through horizontal gene transfer biofilm formation likely plays a role in both of these processes. To understand the genetic mechanisms driving the formation of a biofilm and the role of biofilm formation in E. faecalis pathogenesis we used a genetic method that allows for the identification and characterization of biofilm-specific gene regulatory circuits at all stages of biofilm development. We refined a Recombinase-Based In Vivo Expression Technology (RIVET) system to identify promoters that are specifically expressed during E. faecalis biofilm formation. Screening of the RIVET library yielded 68 unique clones containing biofilm activated genomic segments, including several putative promoters driving expression of genes previously found to be involved in biofilm formation in other organisms, as well biofilm-activated genes of unknown function. Using qPCR we have demonstrated induced transcription of several RIVET-identified genes including EF_1809. EF_1809 has been annotated <www.tigr.org> as a GntR-family transcriptional regulator. This gene has not yet been functionally characterized in E. faecalis. To understand the role of EF_1809 in biofilm formation in this organism we used allelic exchange to create a non-polar null mutation in this locus. The biofilm formation abilities of this mutant were compared to that of the wild type strain using viable counts after 24 hours of biofilm growth as a measurement. The EF_1809 null mutant was reduced in biofilm formation by more than 90%. This defect was complemented by expressing the cloned EF_1809 gene in trans from a plasmid. Therefore we conclude that EF_1809 plays a significant role in biofilm formation in E. faecalis. We hypothesize that expression of EF_1809 is activated following the initiation of biofilm growth, and that it regulates expression of other genetic determinants required for full development of biofilms. Current efforts are directed toward testing this model and toward determination of the molecular mechanisms of activation of EF_1809 expression during biofilm growth and its regulatory effects on downstream target genes.