Mootz successfully defends PhD thesis

Mootz Defense

Joe Mootz successfully defended his PhD thesis, "Regulation and function of Staphylococcus aureus secreted proteases on biofilm integrity," on Thursday, July 18, 2013.  Mootz is pictured here with his mentor, Alex Horswill, PhD.

Staphylococcus aureus is a known cause of chronic biofilm infections. Recent studies have demonstrated the importance of proteinaceous material in the biofilm matrix. S. aureus secretes at least ten proteases and there is growing evidence that these enzymes have self-cleavage roles that alter biofilm integrity. We analyzed the role of secreted proteases in biofilm formation. Initially, we determined that the overexpression of secreted proteases was responsible for strains lacking sigma factor B (SigB) to form a biofilm. We followed up on these studies by identifying the protease(s) responsible for the phenotype. Using genetic and biochemical approaches, we identified the two extracellular cysteine proteases, SspB and ScpA, as being particularly deleterious to biofilm formation.

In addition, we examined the role of the transcriptional regulator Rot in modulating biofilm formation. Rot was found to be essential for S. aureus biofilm formation through mutation analysis. In regulatory studies, Rot protein levels were high under biofilm conditions and controlled expression experiments demonstrated that intracellular Rot levels modulate biofilm formation. Examination of protease expression and activity revealed that production of secreted proteases are inhibited by Rot. Through collaborative studies, electrophoretic mobility shift assays demonstrated that the inhibition was due to the direct binding of Rot to protease promoters. Chemical and biochemical protease inhibitors were able to restore the biofilm capacity to a rot mutant and follow-up inactivation of protease genes confirmed these findings. The rot mutant was attenuated in a murine catheter model of infection. Altogether, these studies suggest that Rot controls protease production to facilitate S. aureus biofilm formation and demonstrate the importance of coordinated regulation during infection.


Joe is a lifelong resident of Iowa. Although born in Waterloo, he didn’t quite grow up on the “mean streets”, a common misconception. He insists that he is still pretty tough though. As a child, he was particularly interested in dinosaurs and insects. His mother Marilyn fondly remembers a time when she thought he would grow up to be an entomologist. Unfortunately, her dreams were shattered when he graduated from Columbus High School and swore off a career in science. Life has a funny way of messing with people sometimes, and somehow he found himself as a Microbiology major at The University of Iowa. In 2006, Dr. Michael Apicella gave him an opportunity for undergraduate research. During this time his love of science blossomed and he developed an appreciation for research. He also learned what it truly meant to be from Waterloo and to be an Iowan.

After graduating from The University of Iowa, Joe continued working as a research assistant in the Apicella lab until he joined the graduate program in Fall 2008. He joined the Horswill lab in Spring 2009 and began his studies on secreted proteases and biofilm integrity in Staphylococcus aureus. As a graduate student, Joe has published a first author paper and is currently editing a second first author paper done in collaboration with the laboratories of Dr. Victor Torres (NYU) and Dr. Tammy Kielian (UNMC). He has also been listed as a co-author on three additional publications while a member of the Horswill lab. Joe has presented work at four professional conferences, including the International Symposium on Staphylococci and Staphylococcal Infections in Lyon, France. He has received numerous travel awards, a teaching award, and is supported by the NIH Mechanisms of Parasitism Training Grant.

Outside of lab, Joe is a four year member of the Leewenhawks. For those of you who are unfamiliar, this is the prestigious Microbiology softball team. He also enjoys poker, board games, and spending time with his wife. After graduation Joe will stay put in Iowa, continuing his research in the Horswill lab before joining his wife in Chicago.