Randy L Coryell

Microbes, squid and evolution oh my!

Temperature Adaptation of Symbiotic V. fischeri


Marine bacteria encounter a myriad of abiotic factors that can influence survivability and adaptation. Specifically, bacterial symbionts that are environmentally transmitted have dual roles that select for both phenotypic and genetic adaptations that influence survival in the planktonic as well as the symbiotic state. Host animals may shift their native range in response to changing local environmental conditions like temperature, while free-living symbionts need the ability to either migrate with their native hosts or infect novel hosts that are found in their geographical range. The sepiolid squid-Vibrio symbiosis has been a tractable model to examine abiotic factors that influence environmental trade-offs that Vibrio bacteria are subject to while outside the squid. We used an experimental evolution approach to investigate whether adaptation to specific environmental conditions (e.g. temperature) increased the ability of symbiotic bacteria to accommodate new hosts from different geographic areas and temperature regimes. Using physiological measures associated with bacterial ability to initiate and maintain symbiosis (bioluminescence, colonization, growth, biofilm formation), we compared ancestral to evolved strains from a number of Indo-west Pacific populations to determine whether temperature increases the ability of V. fischeri to expand their host range. Furthermore, infection assays indicate that the ability to colonize a novel host by strains from a different geographic origin and host squid is influenced by the temperature regime at which they were evolved, indicating that environmental factors shape symbiont colonization and fitness. Results from this study will provide a better understanding of whether adaptation to abiotic fluctuations affects holobiome fitness, and will give insight to the degree at which climate change influences beneficial associations.

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