Date of Award
6-3-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Microbiology and Immunology
First Advisor
Karen Visick
Abstract
Biofilms are aggregates of bacteria encased in a matrix that shields bacteria from environmental hazards. These structures are formed in response to cues from the environment and drive colonization of new niches. Biofilms can be both beneficial and detrimental. Largely, research focuses on biofilms that have negative outcomes in clinical, environmental, and economical settings. However, the value of beneficial biofilms is recognized and studied. The marine bacterium Vibrio fischeri is part of a model system for studying symbiotic biofilms in a eukaryotic host. V. fischeri produces a transient biofilm at the surface of a specialized light organ and then disperses from the biofilm in order to enter the light organ crypts. Biofilm formation of V. fischeri has been extensively studied, but the process of biofilm dispersion (or seeding dispersal) is understudied. The field also lacks specific tools to study the dispersal process. Here, I identified a gap in knowledge and pursued the development of an assay to study biofilm dispersal of V. fischeri in an in vitro setting. To study the dispersal of V. fischeri, I modified a microscopy based time-lapse imaging assay originally developed to study Vibrio cholerae. Using the time-lapse assay, the whole biofilm formation and dispersal process of V. fischeri was observed. After demonstrating the assay was sufficient to capture this process, I investigated the mechanisms controlling dispersal. Previous studies have shown that calcium is a positive signal for biofilm formation. In the time-lapse assay, it was shown that calcium is required for V. fischeri wild-type strain ES114 to stably attach and form biofilms. The effects of calcium were mediated through the diguanylate cyclase CasA, which senses calcium. Overexpression of CasA led to a defect in dispersion that was dependent on production of the bacterial second messenger c-di-GMP (Bis-(3’,5’)-cyclic dimeric guanosine monophosphate), as a point mutation in the catalytic GGDEF domain, required for c-di-GMP production, largely restored biofilm dispersion. Secondly, I demonstrated that the dispersal factor dbfS, a homolog to the gene discovered in V. cholerae, was also active in V. fischeri. When dbfS was deleted in V. fischeri, biofilms studied in a time-lapse assay had impaired dispersion compared to the WT squid isolate ES114. Inhibition of dispersion in a dbfS mutant was reliant on transcription factor VpsR. Further, a dbfS mutant in V. fischeri also had increased biofilm formation under shaking liquid conditions, a migration defect, and dysregulated bioluminescence. The migration defect was independent of the transcription factor VpsR. These data suggest that DbfS regulates much more than dispersion and may have broad implications for V. fischeri colonization of E. scolopes.
Recommended Citation
Esin, Jeremy, "Interrogating the Dispersal Process and Relevant Genes in Vibrio fischeri" (2025). Dissertations. 4186.
https://ecommons.luc.edu/luc_diss/4186
