Does acclimation to environmental stressors lead to increased disease resilience in a model sea anemone, Aiptasia?

The tropical sea anemone, Aiptasia (Exaiptasia pallida), serves as a model system for corals in the laboratory. Previous research has shown that exposure to elevated salinity resulted in increased tolerance to temperature stress in Aiptasia. Based on this observation, we aimed to determine if acclimation to elevated salinity could lead to improved pathogen resistance. Aiptasia were acclimated to seawater at either 35 ppt (control) or 42 ppt (elevated salinity) over a  ‘short-term’ period (16 days) and ‘long-term’ period  (90+ days). After the acclimation period, Aiptasia were infected with Serratia marcescens PDL100 (a known coral pathogen) at 10^8 colony forming units (CFU/ mL), 10^7 CFU/mL, or remained un-infected. The infected anemones were monitored for 10 days and their mortality was scored daily. Aiptasia acclimated to 42 ppt, over both short- and long-term periods, exhibited a higher survival rate than that of control anemones. We then tested whether pre-exposure to sub-lethal concentrations of S. marcescens could lead to increased survival rates in comparison to naive anemones. Anemones were pre-exposed to 10^7 CFU/mL and those that survived were allowed to recover for 21 days and subsequently re-infected with 10^8 CFU/mL. This resulted in one hundred percent survival of the anemones, suggesting priming of Aiptasia immune system occurred in response to non-lethal concentrations of the pathogen. Our results show, for the first time, increased pathogen resilience as a result of prolonged exposure to elevated salinity in Aiptasia. 

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