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Presumed to be the same. The known coral bacterial pathogenScientific RepoRts | 5:17425 | DOI: 10.1038/srepwww.nature.com/scientificreports/Vibrio coralliilyticus was used as the infectious agent to elicit a defense response in the sea anemone. It is a major coral pathogen known to cause coral bleaching27 and white syndrome in Acropora corals28. It has also been shown to cause disease and mortality in Exaiptasia pallida29. The anemone responds to V. coralliilyticus with darkening of the tissues and retraction of tentacles, followed by complete disintegration of polyp tissues29,30. The disease progression pattern is consistent with the behavior of necrotizing pathogens29. To assess the response of E. pallida anemones to repetitive encounters with the infectious agent, we first determined a sub-lethal exposure of the bacterial pathogen V. coralliilyticus that would allow priming of the host without causing mortality. It was determined that a concentration of 1 ?108 CFU ml-1 of this bacterial agent causes stress and mortality in E. pallida anemones after four days of exposure (Supplementary Fig. S1A online). Within a ten-day bacterial exposure, mortality ranged from 60 to 90 in the anemones (Supplementary Fig. S1A online). However, if anemones were removed from the bacterial challenge, washed, and placed in pathogen-free seawater after the third day of pathogen exposure, anemones would recover and show 100 survivorship comparable to unexposed (control) anemones (Supplementary Fig. S2 online). Based on these results, a sub-lethal challenge of a three-day pathogen exposure at 1 ?108 CFU ml-1 was used for the immune priming experiments. The bacterial challenges were conducted at 30 as it has been shown the virulence in this pathogen increases at temperatures above 28 27,31. We demonstrated that this experimental temperature was not a factor of mortality during the bacterial exposure trials (Supplementary Fig. S1B online). Following these trials, three experiments were performed to evaluate the existence of a priming response. Anemones were first subjected to a sub-lethal exposure of V. coralliilyticus followed by https://britishrestaurantawards.org/members/neck40layer/activity/374729/ resting periods (pathogen-free recovering time from the sub-lethal challenge) of either two, four, or six weeks before exposing the sea anemones again to a lethal exposure (ten day pathogen challenge). It is important to note that none of the anemones died during the resting period or prior to the lethal challenge. The response and survivorship of these anemones (primed group) were compared to anemones that were exposed to a lethal challenge but without prior sub-lethal exposure (non-primed group), and also to a control group in which anemones were never exposed to sub-lethal or lethal bacterial challenges. The results showed that anemones that had previously encountered the pathogen (primed) had a higher survivorship than those anemones that encountered the pathogen for the first time (Fig. 2; Kaplan Meier; Mantel ?Cox Post hoc test, p = 0.0001). The survivorship rate appeared to vary as a function of the lapsed time between the two consecutive pathogen exposures. Anemones exposed to the lethal challenge two and four weeks after the sub-lethal exposure presented seven- and five fold increases in survival, respectively, compared to the non-primed anemones (Fig. 2A-B; Kaplan-Meier; Mantel - Cox Post hoc test; Two weeks, p = 0.031; Four weeks, p = 0.039).