Pérez Morales successfully defends PhD thesis

Tiara Pérez Morales

Tiara Pérez Morales successfully defended her PhD thesis, "Production of and response to the cannibalism peptide SDP in Bacillus subtilis," on Wednesday, July 17, 2013.  Pérez Morales is pictured here with her mentor, Craig Ellermeier, PhD.

The Gram positive soil dwelling bacteria Bacillus subtilis produces spores when encountered with a low nutrient environment. However, B. subtilis can delay spore production by a mechanism known as cannibalism. Cannibalism is a process by which B. subtilis delays commitment to sporulation by killing a subpopulation of its cells. This process involves production of two toxins, SDP and SKF.

SDP is a 42 amino acid peptide with a disulfide bond derived from the internal cleavage of its precursor protein pro-SdpC. pro-SdpC is part of the sdpABC operon. Site directed mutagenesis of the leader signal peptide sequence in pro-SdpC demonstrated that proper signal peptide cleavage was required for SDP production. Additional site-directed mutants of the cysteine residues in pro-SdpC revealed that these are not required for SDP toxic activity. These studies also included deletions within the sdpABC operon and revealed that the two proteins of unknown function, SdpA and SdpB are required for SDP production. Taken together we concluded that SDP production was a multi-step process which required proteins encoded by the sdpABC operon.

Production of SDP induces expression of the sdpRI operon. Encoded in this operon is SdpR, the negative regulator, and SdpI. SdpI is a dual function protein which acts both as a signal transduction protein and a defense against SDP toxicity . SDP is believed to be sensed via SdpI. In response to this sensing, SdpI sequesters SdpR to the membrane and allows for sdpRI expression. In this work, we investigated the role of SdpI, specifically what residues were required for the signaling and immunity functions observed. Our work has identified classes of SdpI mutants which affect either SdpI signal transduction or SDP protection.


Tiara was born in Aguadilla, Puerto Rico. As a young student, she was very involved in Spelling Bee, Chess and Science competitions, which earned her the most bullied student award in school. After graduating from high school, she enrolled at the University of Puerto Rico-Mayaguez Campus where she majored briefly in pre-med before discovering that Microbiology was much cooler. She then became secretary for both Mycology and Microbiology Undergraduate Associations which aided her in finding potential undergraduate research labs. During this time, Tiara participated in undergraduate research at her own university, Kansas State University, and The University of Iowa. After being dazzled by the Midwest, she applied and was accepted into the Department of Microbiology at The University of Iowa in 2007.

Tiara joined Dr. Craig Ellermeier’s lab the following spring. Her project involved studying the requirements for production and response to SDP in B. subtilis. During her years in grad school, she earned a Master’s degree in 2010 and continued onto her Ph.D. studies. She is grateful for the chance to join the Graduate Student Senate, mentor students, and TA in laboratory courses. While in Craig’s lab, Tiara’s work has led to a first-author paper and a second first-author manuscript which will be submitted soon. In addition, Tiara has presented her work at several conferences, including the Molecular Genetics of Bacteria and Phages meeting in Madison, WI, the 55th Wind River Conference on Prokaryotic Biology in Estes Park, CO, and the Annual Biomedical Research Conference for Minority Students Conference (ABRCMS) in St. Louis, MO. She has received travel and poster awards and also earned a graduate student mentor award. In 2012, she was very happy to marry her fellow graduate student, Joe Mootz.

Outside of the lab, Tiara is known for her great cooking, her spicy food tolerance, her love of puffer fish, and her newly found skills in softball. After completing her Ph.D., Tiara will be joining Dr. Michael Federle’s lab at the University of Illinois at Chicago. Her research will focus on identifying important genes involved in production, response, and regulation of the Rgg protein signaling pathways in Streptococcus.