Editors' ChoiceMarine Microbiology

Marine plankton communicate with lipids

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Sci. Signal.  02 Jun 2015:
Vol. 8, Issue 379, pp. ec142
DOI: 10.1126/scisignal.aac6702

Through photosynthesis, marine phytoplankton are responsible for half of the world’s carbon fixation. Interspecies communication between phytoplankton and their predator, zooplankton, is critical for the maintenance of the marine food web and ocean nutrients. Signaling compounds secreted by copepods (one type of grazing zooplankton) increase the production of harmful neurotoxic alkaloids by the algal bloom-forming dinoflagellate, Alexandrium minutum. Selander et al. identified six polar lipids that they named copepodamides A to F, which could be purified from extracts of Centropages typicus, a copepod. Each of the copepodamides contained one of the following fatty acyl groups derived from ω-3: docosahexaenoic acid 22:6Δ4,7,10,13,16,19 (DHA), eicosapentaenoic acid 20:5Δ5,8,11,14,17 (EPA), or stearidonic acid (SDA) 18:4Δ6,9,12,15. Mass spectrometry (MS) analysis of chemically degraded fragments revealed that copepodamides A, B, and C possessed a lipid-based scaffold, which the authors called copepodamide G, coupled to either DHA, EPA, or SDA, respectively, whereas copepodamides D, E, and F contained a copepodamide H lipid-based scaffold coupled to one of the ω-3 derived fatty acyl groups. NMR and MS analysis established that the lipid side chain of copepodamide H was a hydroxylated analog of the isoprenoid phytanic acid and that copepodamide G differed from copepodamide H by only two atomic mass units. Dose-response experiments showed that purified copepodamides A, B, and C were 10 times more potent than copepodamides D, E, and F, when individually tested for induction of toxin by A. minutum. Species of copepods that secreted higher proportions of A, B, or C copepodamides induced the greatest release of toxin by A. minutum. In sea water collected at different depths from the northeast Atlantic Ocean, the copepodamide concentration showed a positive correlation with copepod density and was highest near the surface. This study identifies an interspecies lipid signal used by plankton in an aquatic environment.

E. Selander, J. Kubanek, M. Hamberg, M. X. Andersson, G. Cervin, H. Pavia, Predator lipids induce paralytic shellfish toxins in bloom-forming algae. Proc. Natl. Acad. Sci. U.S.A. 112, 6395–6400 (2015). [Abstract] [Full Text]