Megan Kiedrowski successfully defends PhD thesis

Horswill & Kiedrowski defense

Megan R. Kiedrowski successfully defended her PhD thesis, "Characterization of Staphylococcus aureus extracellular nuclease activity," on Thursday, November 15, 2012.  Kiedrowski is pictured here with her mentor, Alex Horswill, PhD.

Staphylococcus aureus is a cause of chronic disease mediated by the formation of biofilms. The S. aureus biofilm extracellular matrix is known to be dependent on proteins and extracellular DNA (eDNA) but not polysaccharide. Interestingly, S. aureus encodes two extracellular nucleases: secreted nuclease, Nuc, and a second nuclease predicted to be membrane-localized, Nuc2. Because eDNA is an important biofilm matrix component, we hypothesized that one or both nucleases may impact S. aureus biofilms.

Regulation studies identified repressors and activators of nuc expression and showed nuc is repressed under biofilm-forming conditions. Biofilm growth was inhibited using a nuc inducible plasmid, and testing of nuc mutants revealed that biofilm thickness increases two-fold in the absence of Nuc. High molecular weight eDNA accumulated in the nuc mutant, indicating a direct link between Nuc and eDNA to contribute to the biofilm matrix. Overall, nuc expression is tightly regulated in S. aureus biofilms, and Nuc greatly impacts biofilm formation.

Prior to this work, little information was available in the literature regarding Nuc2. We detected Nuc2 activity on the S. aureus cell surface, demonstrating the enzyme is a functional nuclease, and confirmed that Nuc2 is surface-attached, with the C-terminal catalytic domain facing out of the cell. Purified Nuc2 has calcium-dependent DNase activity. Localization to the cell membrane does not impair nuclease activity, and the low activity measured for Nuc2 on S. aureus cells is likely due instead to weak expression. The knowledge that Nuc2 is an active, surface-attached nuclease provides insight into roles Nuc2 may play in biofilms and S. aureus infection.


Megan was born in Wisconsin and grew up in the city of Sheboygan Falls, graduating from Sheboygan Falls High School in 2003. She then moved to Madison, WI to pursue undergraduate studies at the University of Wisconsin. While attending UW-Madison, she studied the Neisseria gonorrhoeae type IV secretion system in Joe Dillard’s laboratory for four years and received her B.S. in Medical Microbiology and Immunology in 2007.
Megan entered the Microbiology PhD program in August 2007, joining Alex Horswill’s laboratory in Spring 2008 to begin research on Staphylococcus aureus biofilms. As a graduate student, she has published a first-author paper on the impact of nuclease on S. aureus biofilms and a first-author review on new treatments for staphylococcal biofilm infections, with a second first-author paper to be submitted soon on S. aureus Nuc2. Megan has been fortunate to present her work at several conferences, including the 5th ASM Conference on Biofilms in Cancun, Mexico, the International Symposium on Staphylococci & Staphylococcal Infections in Lyon, France, and the Biofilm Science & Technology meeting at the Montana State University Center for Biofilm Engineering. She has been supported by a Dean’s Fellowship and received a Baxter Young Investigator Award from Baxter International Inc. for her work on nuclease in 2011.

Outside of lab, Megan is an avid supporter of the Green Bay Packers and Wisconsin Badgers. She loves all things Wisconsin, especially cheese, beer and Aaron Rodgers. Her time is occupied by home-brewing with her boyfriend Nick and caring for her pet parrot, a black-headed Caique named Dolly. She is a known Harry Potter enthusiast and also enjoys cooking, traveling, ultimate frisbee and the jewelry-making arts of glass lampworking and torch enameling.

After finishing her work at the University of Iowa, Megan will be moving to Connecticut to begin a postdoctoral position with Jo Handelsman at Yale University to study the commensal-to-pathogen switch of Enterococcus faecalis.