Date of Award


Degree Type


Degree Name

Master of Science (MS)


Microbiology and Immunology


The symbiosis between the gram-negative marine bacterium Vibrio fischeri and its host Euprymna Scolopes occurs when the bacteria reaches and colonizes the light organ. This pathway to colonization begins in the outer marine environment and finishes within the deep crypts of the light organ, with states of biofilm formation and dispersal in between. This switch between biofilm formation to dispersal is important as the bacteria transitions from the surface on the light organ into a pore leading to the interior of the light organ. This dispersal is regulated by LAP system which is dependent on the second messenger c-di-GMP. Through a combination of shaking biofilm assays and wrinkled colony assays, I disproved the hypothesis that the DGC VF_A0343 produced the c-di-GMP that was locally degraded by PdeV. Instead, my work revealed that the gene replacement mutation (DVF_A0343::Erm) caused polar effects arising from overexpression of VF_A0344 by the upstream erythromycin cassette promoter. An important step between biofilm dispersal and entering into the light organ is the bacterial migration. I also measured the scale of motility arrest that occurs when LitR is overexpressed. I identified a subset of DGCs that contribute to an arrest of motility. The transcriptional regulation that LitR has on these DGCs was measured and determined to be more complex than originally thought with a combination of direct and indirect regulation observed as LitR decreases global c-di-GMP levels. I have also teased out the effect of DGCs and increased c-d-GMP concentration on an increase of luminescence. With more in-depth experiments, the indirect regulation LitR has on the DGCs can be elucidated along with a deeper understanding of the inverse connections between LitR, c-di-GMP levels, and luminescence.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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