Matthew Welch, Professor

Closed (1) Elucidating the role of actin-based motility in Rickettsia pathogenesis

Applications for fall 2021 are now closed for this project.

Rickettsia are obligate intracellular bacteria that cause disease in humans. Upon infection, Rickettsia invade various cell types and escape into the cytosol, where they can hijack components of the host cell to support their survival, replication, and subsequent spread to nearby cells.

Of particular interest is the manipulation of the actin cytoskeleton, mediated by the rickettsial proteins RickA and Sca2. RickA promotes actin polymerization by activating the host Arp2/3 complex, leading to the assembly of short, branched actin filaments. In contrast, Sca2 directly polymerizes actin, generating longer, bundled actin filaments. The force generated by polymerization of actin propels bacteria within the host cell, a process known as actin-based motility (ABM). The Rickettsia species we study, R. parkeri, and its close relatives are unique in that they utilize these two ABM proteins, whereas other bacteria that undergo ABM have evolved to use only one. Why Rickettsia have evolved to use both RickA and Sca2 for ABM has been an enigma.

Our lab has previously generated R. parkeri strains with mutations in the rickA and sca2 genes. We have observed a defect in cell-to-cell spread during infection with the sca2 mutant, suggesting that Sca2-mediated ABM is important for spread. However, the role of RickA-mediated ABM remains poorly defined. The overall goal of this project is to understand the function and regulation of RickA-mediated ABM during Rickettsia infection.

While working on this project, the student researcher will learn various molecular biology techniques such as western blotting, PCR, and gel electrophoresis. These skills will be used to help identify a double mutant containing mutations in both the sca2 and rickA genes. The student will also learn how to culture and infect mammalian cell lines, as well as how to perform immunofluorescence microscopy and growth/survival curves, with the goal of determining the effect(s) of the double mutation on ABM.

After completion of this project, the student may be invited to participate in designing and executing a more independent project related to this research topic.

Day-to-day supervisor for this project: Joseph Tran, Ph.D. candidate

Qualifications: Applicants must be detail-oriented, show a strong work ethic, and demonstrate perseverance. Additionally, applicants should be intellectually curious and motivated to learn to think like a scientist, ask questions, and apply rigor and logic to design experiments and interpret results. Students should have completed general chemistry and biology. While coursework in biochemistry, molecular biology, and microbiology is desired, it is not required.

Weekly Hours: 12 or more hours

Related website: https://mcb.berkeley.edu/labs/welch/