George Walters-Marrah, '20


George Walters-Marrah, '20





I am a junior at UCF majoring in biotechnology and biomedical sciences with an emphasis on molecular microbiology. I find microbial pathogens and how they interact with the environment extraordinarily interesting. I currently study mycobacteria in Dr.Kyle Rohde's research lab at the UCF Burnett School of Biomedical Sciences. My career aspirations are to obtain a Ph.D. relating to immunity and pathogenesis, go into either academia or the biotechnology industry, and possibly start a biotech business based on a conceptual computer program that I am brainstorming about.

Faculty Mentor

Dr. Kyle Rohde

Undergraduate Major


Future Plans

Ph.D. in Immunology


Project title: Investigating the role of the DosRS and PhoPR 2-component systems in the pathogenesis of Mycobacterium abscessus

Conducted at the University of Central Florida

Mentor: Dr. Kyle Rohde, Ph.D., Burnett School of Biomedical Sciences, University of Central Florida

Project Abstract: Mycobacterium abscessus (Mabs) is an environmental microbe that is pervasive in bodies of water, decomposing vegetation, and urban water sources. It has quickly become known as the most infectious, persistent, and drug-resistant of the rapid growing non-tuberculous mycobacteria. Mabs has been linked with traumatic wound infections, tuberculosis-like pulmonary infections, and formation of granuloma lesions. Currently, there is a shortage of potent anti-virulence drugs against Mabs. Little is known about the molecular mechanisms underlying the ability of Mabs to persist in the host. However, the 2-component systems (2CS), DosRS and PhoPR, are crucial in the ability of Mycobacterium tuberculosis (Mtb), a close relative of Mabs, to become pathogenic – via sensing of hypoxia (DosRS) and acidic pH (PhoPR). DosRS and PhoPR have been confirmed to also be present in Mabs. In this study, molecular microbiology techniques will be used to knock out DosRS and PhoPR, and essentially make a Mabs mutant for each 2CS. Subsequently, the mutant Mabs strains will be tested in order to observe if they retain the capacity to persist through unfavorable conditions. It is expected that the 2CS in Mabs will be of similar importance to the set found in Mtb. If the expectations hold true, the mutants will be heavily attenuated. Therefore, DosRS and PhoPR could possibly be excellent targets for further experimentation with the intention of making a viable anti-virulence drug for Mabs. This study will give insight into the pathogenesis and virulence of Mabs and may lead to future experiments.

Summer Research

Project title: Investigating the significance of acetylation by HopZ3 in Pseudomonas syringae

Conducted at the University of Chicago as part of the Molecular Genetics and Cell Biology REU

Dr. Jean Greenberg, Ph.D., Department of Molecular Genetics and Cell Biology, University of Chicago

Project Abstract: Pseudomonas syringae (Psy) is a bacterial plant pathogen and the causative agent of leaf spot. Psy’s success is largely due to its type III secretion system (T3SS) that enables it to inject a large repertoire of effector proteins into plant cells. The effector protein HopZ3 has been shown to suppress immune responses and promote bacterial growth. HopZ3 can bind to and acetylate the effector protein AvrPto and the tomato protein Pto, a member of the Prf immune complex found in tomato. Pto recognizes and interacts with AvrPto to activate the immune response during infection, but HopZ3-mediated acetylation reduces AvrPto-Pto interactions. This suggests that the acetylation sites found on AvrPto play a part in AvrPto-Pto interactions. This study focuses on the significance of two histidine acetylation sites found on AvrPto and their roles in detection and binding by Pto to activate the plant immune response. In vitro pull-down assays were used to test the importance of HopZ3- mediated histidine acetylation sites in AvrPto-Pto interactions. It was expected that a mutation of the histidine residues to alanine will have a similar effect as acetylation by HopZ3. Additionally, it is suspected that acetylation by HopZ3 can occur before secretion. This would give Psy a notable advantage because HopZ3 would be able to acetylate AvrPto before Pto is in the vicinity to perform a binding reaction. Therefore, AvrPto proteins, isolated from Psy induced by infection conditions, will be analyzed using mass spectrometry (MS) for signs of acetylation before secretion in vivo. These experiments gave insight into the specific mechanisms used by HopZ3 to suppress plant immune responses. It was found that mutation of the histidine acetylation sites on AvrPto does not compromise AvrPto-Pto interactions. And, AvrPto was expressed successfully in Psy and the protein was collected in T3SS-inducing conditions. AvrPto bands were cut and sent for MS analysis to detect possible acetylated residues.

Summer Research Institution

University of Chicago (NSF REU)


Medicine and Health Sciences

George Walters-Marrah, '20