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Evidence that glucose is the major transferred metabolite in dinoflagellate–cnidarian symbiosis
Matthew S. Burriesci, Theodore K. Raab, John R. Pringle


Reef-building corals and many other cnidarians are symbiotic with dinoflagellates of the genus Symbiodinium. It has long been known that the endosymbiotic algae transfer much of their photosynthetically fixed carbon to the host and that this can provide much of the host's total energy. However, it has remained unclear which metabolite(s) are directly translocated from the algae into the host tissue. We reexamined this question in the small sea anemone Aiptasia using labeling of intact animals in the light with 13C-bicarbonate, rapid homogenization and separation of animal and algal fractions, and analysis of metabolite labeling by gas chromatography-mass spectrometry. We found labeled glucose in the animal fraction within 2 min of exposure to 13C-bicarbonate, whereas no significant labeling of other compounds was observed within the first 10 min. Although considerable previous evidence has suggested that glycerol might be a major translocated metabolite, we saw no significant labeling of glycerol within the first hour, and incubation of intact animals with 13C-labeled glycerol did not result in a rapid production of 13C-glucose. In contrast, when Symbiodinium cells freshly isolated from host tissue were exposed to light and 13C-bicarbonate in the presence of host homogenate, labeled glycerol, but not glucose, was detected in the medium. We also observed early production of labeled glucose, but not glycerol, in three coral species. Taken together, the results suggest that glucose is the major translocated metabolite in dinoflagellate–cnidarian symbiosis and that the release of glycerol from isolated algae may be part of a stress response.


  • Supplementary material available online at http://jeb.biologists.org/cgi/content/full/215/19/3467/DC1


    This study was supported by the National Science Foundation [EAGER grant IOS-1138275], the Gordon and Betty Moore Foundation [grant 2629] and the National Institutes of Health [training grant 5 T32 HG000044]. Deposited in PMC for release after 12 months.


    artificial seawater
    gas chromatography
    mass spectrometry
    N-methyl-N-trimethylsilyl tri-fluoroacetamide
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