Date of Award
1-1-2024
Document Type
Thesis
Degree Name
M.S. in Biological Science
First Advisor
Peter Zee
Second Advisor
Colin Jackson
Third Advisor
Erik Hom
School
University of Mississippi
Relational Format
dissertation/thesis
Abstract
Stressors are ubiquitous factors in biological systems that result in deviations from an organism's optimal physiological state, potentially causing fitness decreases. Stressors can be biotic (e.g., predators, parasites, competitors) or abiotic (e.g., pH changes, temperature, environmental toxins). Persistent stress can lead to population declines unless organisms respond through mechanisms such as evolutionary adaptation. Experimental evolution with microorganisms, particularly bacteria, is a powerful method for studying these phenomena due to their short generation times, large populations, as well as the ability to control their environment, and freeze and revive populations. Bacteria-phage systems, such as Pseudomonas fluorescens SBW25 and its lytic phage Phi2, are well-established study models for coevolutionary studies. In this research, I studied the responses of Pseudomonas fluorescens SBW25 to multiple stressors across different timescales. In Chapter One, I examined the long-term (10 bacterial growth cycles) effects of coevolving with phage Phi2 on P. fluorescens SBW25 traits such as growth rate in the absence of stress, resistance to the ancestral phage genotype, and resistance to the antibiotic kanamycin. I found a trade-off between the effects of ancestral phage and kanamycin. In Chapter Two, I investigated the short-term (single bacterial growth cycle) effects on bacterial population growth of introducing phage and antibiotics in different orders and timings. I aimed to understand how the order and timing of the stressors impact the synergism and antagonism among the effects of these antibacterial agents (i.e. bacteriophage or antibiotics) on the bacteria. I did not find significant effects of order and timing of stressors. I did find a significant influence of bacterial phenotype, where synergism between phage and antibiotics was evident in phage-resistant bacteria. This research highlights the complexity of responses to multiple environmental stressors, and their interactions, a scenario that is common across all biological systems.
Recommended Citation
Burchfield, Parisa, "Effects of Multiple Stressors on Pseudomonas Fluorescens Over Short and Long Timescales" (2024). Electronic Theses and Dissertations. 2924.
https://egrove.olemiss.edu/etd/2924