Document Type
Dissertation
Date of Award
2026
Degree Name
Doctor of Philosophy (PhD)
Department
Basic Biomedical Science
First Advisor
Michael MC Chaussee
Abstract
In Streptococcus pyogenes, bacteriophages and other horizontally transmissible elements (HTEs) comprise approximately 10% of the genome, and each clinical isolate carries a unique combination of these elements, contributing to genetic diversity, virulence, antibiotic resistance, and immune evasion. Previously, our laboratory identified binding sites of the transcriptional regulator Rgg1 in the clinical isolate NZ131 and demonstrated that Rgg1 influences genome-wide gene expression, including bacteriophage genes. In the clinical isolate SF370, the prophage SpyCIM1, positioned in the chromosome between the mutL and mutS genes, controls DNA mismatch repair through excision and reintegration into the chromosome. In the integrated form, the prophage displaces mutS from the bicistronic mutLS promoter. In this study, we used a mutant strain of SF370 lacking SpyCIM1 and created mutants lacking rgg1 to investigate the role of SpyCIM1 in Rgg1-mediated gene regulation. We hypothesized that bacteriophage SpyCIM1 alters the transcriptome and phenotype of S. pyogenes either through direct interaction with Rgg1 or by influencing Rgg1-mediated excision and reintegration dynamics. To test this, we performed RNA-Seq to characterize the Rgg1 regulon in the presence and absence of SpyCIM1. We also used PCR to assess SpyCIM1 excision and integration frequencies. Suspecting that the mobility of the island into and out of the chromosome was responsible for changes in gene expression associated with SpyCIM1, we created a specific knock of the islands int4 gene, which appeared likely to mediate integration and excision. Following the PCR analysis, we performed RNA-Seq to evaluate whether the mobility of SpyCIM1 affects Rgg1-dependent gene regulation. Finally, we used a mouse model to examine the impact of SpyCIM1-Rgg1 interactions on virulence. Our results suggest that Rgg1, influenced by SpyCIM1 and its mobility, regulates genes involved in metabolism and virulence, potentially affecting infection severity.
Subject Categories
Medical Microbiology | Medical Molecular Biology
Keywords
Not Given
Number of Pages
106
Publisher
University of South Dakota
Recommended Citation
Tian, Yuan, "THE ROLE OF BACTERIOPHAGE IN THE RGG1-MEDIATED VIRULENCE CONTROL OF STREPTOCOCCUS PYOGENES" (2026). Dissertations and Theses. 431.
https://red.library.usd.edu/diss-thesis/431