Effect of Signaling Molecules on Strain Diversity of the Euprymna-Vibrio Symbiosis
Open Access
- Author:
- Ehrig, Molly
- Area of Honors:
- Biology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Timothy Iwao Miyashiro, Thesis Supervisor
Yingwei Mao, Thesis Honors Advisor - Keywords:
- Quorum Sensing
Evolution
Strain Diversity
Symbiosis
Vibrio fischeri
Euprymna scolopes
Bacteria
Squid - Abstract:
- Most animals form long-term associations with bacteria that are crucial for the health and fitness of both organisms. These symbiotic relationships often involve bacterial communities comprised of different taxa. There can be genetic variation within a single bacterial species, i.e., strain diversity, which affects community structure and function. The selective pressures that lead to strain diversity remain unknown. This work aims to close this knowledge gap by investigating adaptations that result from exposure to bacterially-derived products within a population as a mechanism for strain diversity. The symbiosis between the Hawaiian bobtail squid Euprymna scolopes and the bacterium Vibrio fischeri provides the opportunity to study this phenomenon. V. fischeri produce bioluminescence to camouflage the host via quorum sensing, a process by which populations coordinate the expression of traits by detecting the concentration of signaling molecules called autoinducers. V. fischeri populations reside in multiple, spatially segregated sites within the host, naturally varying the concentration of autoinducer. The purpose of this work is to evaluate whether autoinducer is a selective pressure that drives the evolution of V. fischeri. In this study, a novel strain of V. fischeri was isolated from a wild-caught adult Hawaiian bobtail squid and characterized for its ability to respond to autoinducer and establish symbiosis. V. fischeri was then propagated in the presence of autoinducer and evaluated for mutations and resulting phenotypes, including bioluminescence response to autoinducer, biofilm formation, and symbiosis establishment. We demonstrate that the presence of autoinducer molecules leads to adaptations in the V. fischeri quorum-sensing system in vitro by promoting the loss of the ability to respond to autoinducer, thereby generating strain diversity.