Date of Award

Spring 2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Chemistry & Biochemistry



Committee Director

Erin B. Purcell

Committee Member

Lesley H. Greene

Committee Member

Alvin A. Holder

Committee Member

Patrick C. Sachs


The human pathogen Clostridioides difficile is increasingly tolerant of multiple antibiotics and causes infections with a high rate of recurrence, creating an urgent need for new preventive and therapeutic strategies. The stringent response, a universal bacterial response to extracellular stresses, governs antibiotic survival and pathogenesis in diverse organisms but has not previously been characterized in C. difficile. This dissertation explores the ability of C. difficile to mount the stringent response. The bacteria encode a full-length, canonical bifunctional Rel/Spo Homolog or RSH enzyme. C. difficile RSH is incapable of utilizing GTP as a substrate but readily synthesizes putative 5’-pGpp-3’ alarmones. Transcription of rsh is stimulated by bacterial stationary phase onset, nutrient limitation, and exposure to the antibiotics clindamycin and metronidazole. Transcriptional suppression of rsh increases bacterial antibiotic susceptibility, suggesting that RSH contributes to bacterial antibiotic tolerance and survival. Chemical inhibition of RSH by the 5’-ppGpp-3’ analog Relacin similarly increases antibiotic susceptibility in epidemic C. difficile, indicating that RSH inhibitors are a viable strategy for drug development against Clostridioides difficile infection. Finally, mechanisms contributing to C. difficile host colonization and aspects of bacterial behavior during infection remain unclear. Therefore, this dissertation also explores nutrient-derived motility regulation of the pathogen during host intestinal mucus colonization. An epidemic C. difficile strain suppresses motility in the presence of high unchained N-acetylneuraminic acid, an intestinal mucus component. The observed motility suppression is independent of bacterial tumbling but robust single species biofilm formation by R20291 and motility suppression in response to high NEU5A concentration may be regulated by the same signaling network(s).


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