The Diversity of Co-isolated Strains of Vibrio fischeri Reveals New Insights into the Establishment of Multistrain Symbioses

Restricted (Penn State Only)
- Author:
- Donnelly, Aidan
- Area of Honors:
- Microbiology
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Timothy Iwao Miyashiro, Thesis Supervisor
Teh-Hui Kao, Thesis Honors Advisor - Keywords:
- Vibrio fischeri
Euprymna scolopes
Symbiosis
Strain diversity
Bacteria
Squid
Bioluminescence
Quorom Sensing
SD50
Host-microbe
Mutualism
Co-isolated - Abstract:
- Many animals depend on associations with bacterial symbionts for normal physiology. Hosts often harbor different strains of bacterial symbionts that exhibit a broad diversity of symbiotic traits. Though it is well appreciated that many symbioses promote the health of animals, the contribution of this strain diversity to symbioses remains poorly understood yet vital to predicting how symbioses assemble and function. The mutualistic symbiosis between the Hawaiian bobtail squid, Euprymna scolopes, and the bioluminescent marine bacterium, Vibrio fischeri, is a powerful model to study strain diversity because wild-caught animals routinely harbor 5-6 different strains. This thesis describes efforts to understand how strain diversity assembles within a host by characterizing strains of V. fischeri that were isolated directly from the tissue homogenate of the light organ of a wild-caught adult squid. Whole-genome sequencing and multi-locus sequence typing (MLST) revealed three distinct strains within the homogenate sample. The phenotypic diversity associated with these strains was determined by assessing their ability to form biofilms, swim, grow in isolation or with other strains, and produce bioluminescence, which together revealed insight into the symbiotic traits of co-isolated strains. Additionally, to determine how effectively the three co-isolated strains could colonize juvenile animals, colonization assays were performed individually and in concert with other co-isolated strains. Broad diversity in colonization ability was observed between the co-isolated strains which was defined using a 50% symbiotic dose methodology that is novel to the field. Though the same consortia were able to be reconstituted in juvenile squid, it was observed that interactions between the strains limited their overall ability to access crypt spaces, and no co-colonized crypt spaces were observed. Taken together, these results have led to a model that offers an explanation of how these co-isolated strains became associated with the original E. scolopes specimen and provides new insight into the establishment of multistrain symbioses.