Author ORCID Identifier:
Date of Graduation
8-2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy in Cell & Molecular Biology (PhD)
Degree Level
Graduate
Department
Cell & Molecular Biology
Advisor/Mentor
Wang, Yong
Committee Member
Jingyi Chen
Second Committee Member
Kyle Quinn
Third Committee Member
Mary Savin
Abstract
Bacterial motility is crucial for survival, adaptation and disease progression across environments such as soil, host tissues, and biofilm. Bacterial motility in such complex porous microenvironments not only governs how bacteria move through the physical barriers but also plays an important role in processes that are significant to the human health and environment, like improved drug delivery, enhanced treatment efficacy, and more effective bioremediation in contained and structured environments. Despite the importance, how bacteria behave and navigates in a media, where physical confinement and spatial heterogeneity dominates, is not fully understood. This dissertation studies the motility of Escherichia coli in microscale porous environments by using both natural systems and synthetic biomimicking systems, to systematically investigate the effects of confinement on the bacterial movement and flagellar dynamics. Three different experimental systems were studied: (i) Two dimensional porous media mimicked by microspheres, (ii) aqueous micro-environments with natural soil particles, and (iii) biologically relevant hydrogel that simulate mucosal layer or the extracellular matrix. Quantitative imaging methods and trajectory analysis were used to study the bacterial motion and filament behavior. In synthetic porous media mimicked by polystyrene microspheres, bacterial velocity decreased and directional reorientation increased with higher microsphere density. In natural soil microenvironments, bacterial movement was further influenced by factors such as particle size, void fraction and proximity to soil particles. Bacterial velocities showed positive correlation with particle size and a negative correlation with void fraction, while directional changes increased near the soil surface, emphasizing the ecological relevance of soil structure in microbial transport. In hydrogel environment mimicking host associated viscoelastic barriers, direct visualization of fluorescently labelled flagellar filaments revealed confinement induced structural transitions like unbundling, looping, kinking, and curling, which were associated with distinct motility types termed as SWIM, TRAP, and STALL. These motility types were marked with progressive reductions in translational motion and coordination of the flagella bundle. Together, these findings highlight how physical constraints imposed by pore-scale architecture influence bacterial behavior at both whole-cell and flagellar levels, revealing that while the intrinsic motility mechanisms in E. coli remains intact, their mobility and flagellar configuration are strongly influenced by the geometry of the surrounding microstructure. This work provides an integrated, multiscale understanding of bacterial motility in complex porous systems, with its applications in microbial ecology, infection biology, and design of biomimetic porous materials.
Citation
Shrestha, D. (2025). Understanding Bacterial Interactions and Motility in Complex Porous Micro-Environments. Graduate Theses and Dissertations Retrieved from https://scholarworks.uark.edu/etd/5871
