Zimbeck successfully defends MS thesis

Zimbeck Cake

Alicia Zimbeck successfully defended her MS thesis, "Fate of Francisella tularensis Capsule and O-antigen Mutants in Human Macrophages," on Monday, April 21, 2014. Alicia is pictured here with her mentor, Lee-Ann Allen, PhD.

Francisella tularensis is the causative agent of tularemia and is categorized by the CDC as a Tier 1 select agent. This gram-negative bacterium infects macrophages by escaping the phagosome and replicating with high efficacy in the cytosol. Biosynthesis of F. tularensis capsule and LPS O-antigen requires the O-antigen biosynthesis gene cluster. Mutations in this gene cluster not only result in serum sensitivity, but also attenuate the ability to cause disease in vivo. Different capsule and O-antigen mutants appear to have distinct intracellular phenotypes in macrophages, including loss of replication. One explanation for this loss in mutant replication is capture and degradation by the host cell’s autophagy pathway, which is an accepted innate immune response for many intracellular pathogens. However, bacteria have developed methods to circumvent recognition and degradation by autophagy. We propose that capsule and O-antigen help F. tularensis evade detection by autophagy during intracellular infection.

During my studies I characterized nine different capsule and O-antigen mutants, and found diverse replication phenotypes in MDMs and varying degrees of MDM cytotoxicity. Also, only a subset of the mutants was detected by ubiquitin, supporting our hypothesis that different capsule and O-antigen mutants have diverse fates in MDMs. I also found that LVS and Schu S4 wbtA mutants had similar phenotypes. In support of our hypothesis that capsule and O-antigen mutants are more susceptible to autophagy, we found that LVS wbtA more readily colocalized with ubiquitin, autophagy receptors, and the autophagy membrane protein LC3B, but not Beclin-1 or LAMP-1. Since we did not observe LAMP-1 colocalization, there may be defects in the maturation of autophagosomes to degradative autolysosomes. Finally, we found that the fate of LVS wbtA in MDMs is dissimilar from J774 macrophages, suggesting macrophage species affect mutant fate. This thesis shows that different capsule and O-antigen mutants have multiple fates in MDMs, and suggests that F. tularensis capsule and O-antigen prevent detection by autophagy.


Alicia Zimbeck grew up in Westminster, CO, with an amazing and supportive family. Together, Alicia and her family spent most of their free time camping and driving to Iowa to visit relatives. After Alicia’s sophomore year in high school, her family moved to Marshalltown, IA, where Alicia discovered a newfound appreciation for science through activities like Science Olympiad. This excitement for science spurred Alicia’s decision to complete a double major in biochemistry and biology at Wartburg College in Waverly, Iowa. Upon graduation in 2009, Alicia matriculated into the Emerging Infectious Diseases Laboratory Fellowship through the APHL and CDC. During this time Alicia worked with Dr. Shawn Lockhart at the CDC in Atlanta, GA, on FKS mutants in Candida glabrata and their resistance to echinochandin drugs. One year later, Alicia began her graduate career in the Biosciences program at The University of Iowa. Beginning in 2011, Alicia entered the department of Microbiology and began her work with Dr. Lee-Ann Allen. Alicia has enjoyed working in the lab and has not been afraid to sing and dance while doing so.

Post-graduation, Alicia will start the Medical Laboratory Science Program at St. Luke’s Hospital in Cedar Rapids. Alicia is looking forward to spending more time with family, swimming, doing arts and crafts, traveling around the world, and getting married in the fall. Alicia wishes to thank everyone who has helped and supported her though the many phases of her life and getting her to where she is today.