Graduation Year


Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts



Reader 1

Pete Chandrangsu

Reader 2

Findley Finseth

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Rights Information

2021 Anna J Bagley


In response to the growing rates of antibiotic resistant infections, this study aims to understand how bacteria respond to metal stress in order to combat transmission and formation of antibiotic resistant infections with the reintroduction of metals as antimicrobials. Poly-gamma-glutamic acid, or ๐›พ-PGA, is produced by B. subtilis as part of a stress response, acting as a physical barrier from adverse conditions. In this study, an experimental evolution approach was taken, repeatedly exposing B. subtilis to high concentrations of Zn2+. Two strains were identified that showed significant phenotypic differences when compared to wild type and were sequenced using next generation, whole genome sequencing. A frameshift mutation in rex was found in both strains, a gene not previously connected to the production of PGA. A mutation in this gene resulted in a significantly lowered ๐›พ-PGA yield when grown in the presence of Zn2+ when compared to wild type B. subtilis, and conferred increased resistance against metal toxicity as seen by growth curve analyses. I propose a new model of ๐›พ-PGA production that relies on metabolic fluxes that are impacted by the genes regulated by Rex. In summary, this study identifies a new gene involved in the production of ๐›พ-PGA through an experimental evolution approach and proposes a new model connecting the regulator Rex and metabolic fluxes to the biosynthesis of ๐›พ-PGA.

This thesis is restricted to the Claremont Colleges current faculty, students, and staff.