Abstract: Ecological Diversification of Vibrio fischeri During the Free-Living Phase and the Subsequent Consequences of this Bioluminescent Microbe to Grow Along a Salinity Gradient

The mutualism between sepiolid squids and the marine bioluminescent bacterium Vibrio fischeri has become an established tractable model for studying associations between prokaryotic symbionts and their eukaryotic animal hosts, since both participants can be maintained independently of each other in the laboratory (Soto et al. 2014). Within the squid host, V. fischeri cells reside in a specialized and complex morphological structure called the light organ, where they benefit from the inhabitance of a microenvironment rich in nutrients relative to the open ocean. In return, the squid utilize light produced by the bacteria for a cryptic behavior called counterillumination (Soto et al. 2009).

Salinity is a major factor in determining the distribution of the Vibrionaceae throughout the world’s oceans and other aquatic habitats, such as river deltas and lagoons (Soto et al. 2009). My research in Dr. Soto’s lab this summer will focus on growing V. fischeri on a salinity gradient to assess how ecological diversification affects stress physiology. For thirteen strains, microbial growth of the V. fischeri wrinkly spreader ecotype will be compared to the smooth colony forming ancestor along a salinity gradient. The possibility exists that adaptive radiation of V. fischeri during the free-living phase may affect this microbe’s ability to reproduce along a salinity concentration gradient. Previous research has shown that differences in the capacity to grow at different sodium chloride concentrations can affect the host expansion range of V. fischeri in cephalopod hosts (Soto et al. 2014).