Date of Award

Winter 2025

Project Type

Dissertation

Program or Major

Microbiology

Degree Name

Doctor of Philosophy

First Advisor

Cheryl Whistler

Second Advisor

Stephen Jones

Third Advisor

Karen Visick

Abstract

Vibrio fischeri strains vary in their capacity to form mutualisms with animal hosts such as the Hawaiian bobtail squid Euprymna scolopes, yet these differences are often not explained by phylogeny. Successful colonization requires biofilm production, which is tightly controlled by a complex network of two-component system regulators including hybrid histidine kinases BinK and RemK, as characterized in the model symbiont strain ES114. Divergence in biofilm network architecture or regulatory logic may lead to strain-specific differences in biofilm formation, limiting symbiotic potential. Part I of this work investigates genetic divergence underlying reduced colonization capacity in strain H905, a planktonic isolate and close relative of ES114, to explore how to explore the genomic basis of adaptation to vastly different ecological niches. Using comparative genomics and phenotypic assays, we identified a novel genomic island in H905 (H905GI1) that encodes a hybrid histidine kinase GbrK and an RTX-toxin with accompanying secretion system, suggesting adaptation to an ecological niche distinct from E. scolopes colonization. Whereas ES114 produces both symbiotic polysaccharide (Syp) and cellulose biofilm substrates through context-dependent regulation by the hybrid histidine kinases BinK and RemK, H905 exhibits divergent signaling network architecture. H905 lacks cellulose production due to disruption of the cellulose operon and instead produces an unknown, calcium-induced polysaccharide repressed by BinK and GbrK. GbrK strongly represses Syp production and colonization, overriding the influence of RemK in the strain. Loss of GbrK and BinK is required for H905 to visibly produce Syp, with loss of either regulator restoring colonization potential. These results demonstrate how the horizontal acquisition of novel regulators can rewire core pathways controlling symbiosis and drive ecological divergence between closely related V. fischeri strains.Nursing students frequently struggle to learn and apply microbiology, a foundational component of nursing education linked to clinical effectiveness and patient outcomes. One contributing factor may be utility value (UV), the belief that microbiology knowledge is relevant to future goals such as a nursing career, which strongly predicts academic motivation, persistence, and achievement. Though other task values such as interest and cost of learning also impact learning, different strategies to increase UV are often targeted in STEM curriculum interventions. However, no studies have examined the impact of UV interventions for nursing students to increase relevance of microbiology to nursing practice. Part II of this dissertation investigates how two UV interventions affect perceptions of microbiology UV in nursing students: a directly-communicated approach using a nursified curriculum (Treatment 1), and the same curriculum paired with a self-generated UV writing assignment (Treatment 2). Analysis of pre- and post-surveys revealed that although nursing students began with higher UV than their non-nursing peers, their UV declined significantly in Treatment 1, erasing the initial advantage. In contrast, UV was maintained in Treatment 2 and remained significantly higher than in Treatment 1. Regression analyses further revealed that gains in interest predicted increases in UV only when the perceived cost of learning decreased, highlighting the interdependence of task values. These findings suggest that combining directly-communicated and self-generated UV interventions may offer a scalable strategy to improve microbiology UV for nursing students, supporting both academic success and beneficial healthcare outcomes.

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