Graduation Year

2023

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Cell Biology, Microbiology, Molecular Biology)

Major Professor

Larry J Dishaw, Ph.D.

Co-Major Professor

Lindsey Shaw, Ph.D.

Committee Member

Prahathees Eswara, Ph.D.

Committee Member

Sophie Darch, Ph.D.

Keywords

Shewanella fidelis, bacteriophage predation, Ciona innate immune effector, VCBP

Abstract

Current microbiome studies have shown that the maintenance of homeostasis betweenmicrobial populations (e.g. bacteria, viruses) and the host immune system (e.g. innate immune molecules) is necessary for balancing health and disease outcomes within the host. These studies most often utilize vertebrate models; however, research in this field can benefit from diverse model systems that facilitate our ability to conduct experiments to identify phylogenically conserved rules influencing homeostasis in the gut of animals. The Dishaw has developed the use of a filter-feeding marine invertebrate chordate, Ciona robusta, to model such fundamental interactions[1]–[6]. While most biological diversity and functional contribution within microbiomes is often attributed to bacteria, two often overlooked but important features of the system exert very strong influences worthy of study: strain-level variation and viral predation of bacteria. The former is a common outcome of some selective pressures faced by bacteria and the latter is mediated by bacteriophages, or phages for short. In addition to evaluating these microbial interactions in the gut microbiome, this study evaluated how host immune factors influence the outcome of these polymicrobial interactions, and how they may shape homeostasis. Thus, the current study explored simple questions regarding phage infection of bacteria, strain variation among some relevant strains, and interactions with host immunity. I focused specifically on a host immune effector, a variable region-containing chitin-binding protein or VCBP, that is predominantly expressed in the gut of Ciona. This study identified trends between gut isolates including examples of broad host viral infection, ability for a host immune effector to differentially respond to microbial communities, and generated a pangenome to reveal a core genome between strain-level variants despite having varying phenotypes in vitro, and ultimately, gained insight into existing relationships between microbial communities in a microbiome.

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