Establishment of a model for chemoattraction of Symbiodinium and characterization of chemotactic compounds in Acropora tenuis
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Corals harbor symbiotic dinoflagellates, Symbiodinium spp., acquired from surrounding environments. Because Symbiodinium are present at low densities in the water column, corals may attract these symbionts using chemotactic compounds. To examine whether corals contain chemotactic compounds, we established an assay to measure the chemotactic activity for Symbiodinium using an extract of the coral Acropora tenuis, a major reef-building coral in Japan. Our assay revealed that Symbiodinium strain NBRC102920 (clade A), which is taken up by juvenile A. tenuis polyps, is attracted to crude A. tenuis extracts. We found that the chemotactic compounds are water-soluble, heat-labile macromolecules and that the chemotactic activity was inhibited by N-acetyl-d-glucosamine (GlcNAc). We separated the GlcNAc-binding fraction (Fr-ActL) and identified it as the most plausible candidate for the chemoattractant, since the chemotactic activity of the crude A. tenuis extract appeared to be mainly attributable to the activity of Fr-ActL and was also inhibited by the addition of GlcNAc. These results indicate that chemoattraction is mediated via the binding of Symbiodinium to Fr-ActL.
KeywordsAcropora tenuis Coral Symbiodinium Chemoattraction Lectin
The authors would like to thank Dr. Hiroshi Yamashita for useful advice on the preparation of this manuscript. This work was supported by a Grant-in-Aid for Scientific Research (C) from the Ministry of Education, Culture, Sports, Science and Technology of Japan to MJ  and partially by a grant-in-aid from The Mikimoto Fund for Marine Ecology, Japan.
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