Date Thesis Awarded

5-2021

Access Type

Honors Thesis -- Open Access

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Kurt Williamson

Committee Members

Lizabeth Allison

Mark Forsyth

Douglas Young

Abstract

Viruses are the most abundant biological entities on Earth. Viral impacts are evident from the level of individual cells and population all the way up to ecosystems and global elemental cycles. Since bacteriophages (viruses that infect bacteria) were first identified in the early twentieth century, the study of these fascinating entities has shown how viral dynamics within ecosystems can influence microbially-mediated processes at a large scale. Viral infections can impact hosts and host-mediated processes in in multiple ways, one of which is through cryptic infections. This state, in which a bacterium may harbor a cryptic phage infection, is known as lysogeny. Such infections provide an evolutionary advantage to the phage, to survive times when host cells are scarce or few progeny can be made. Further, such infections may provide advantages to the host cell, as alleles carried by the phage genome may impact host phenotype. These cryptic infections can be activated (induced) chemically through laboratory assays, enabling us to determine the extent of lysogeny within bacterial assemblages. Most of the information we possess regarding lysogeny has come from research in aquatic ecosystems; however, the few studies that have investigated lysogeny in soil bacteria suggest that this is an important mechanism for phage replication and survival in soil environments. This study aimed to elucidate potential temporal trends in lysogeny in soil bacterial communities, as well as to compare the efficacy of inducing agents commonly used in induction assays. After collection and analysis of soil samples over a six-month period, results suggested that samples from only two out of six months showed evidence of prophage induction. Subsequent experiments compared induction responses of soil and aquatic bacteria, and the lysogenic bacterium E. coli W3104, to six different inducing agents. Results were highly variable; while most inducing agents, particularly mitomycin C, did appear to generate an increase in extracellular phage particles, few of these increases were accompanied by bacterial lysis. This is important because determinations of lysogeny within bacterial communities depends on both increases in phage abundance and decreases in bacterial abundance in order to score the response. These results suggest that a reevaluation of the ways in which lysogeny is measured may be necessary, as calculations based on induction assays frequently return biologically nonsensical results. This study offers data supporting the prevalence of lysogeny within soil bacterial communities, and proposes potential directions for future research in this field.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Available for download on Saturday, May 14, 2022

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