Corals and other cnidarians house photosynthetic dinoflagellate symbionts within membrane-bound compartments inside gastrodermal cells. Nutritional interchanges between the partners produce carbohydrates and lipids for metabolism, growth, energy stores, and cellular structures. Although lipids play a central role in the both the energetics and the structural/morphological features of the symbiosis, previous research has primarily focused on the fatty acid and neutral lipid composition of the host and symbiont. In this study we conducted a mass spectrometry-based survey of the lipidomic changes associated with symbiosis in the sea anemone Aiptasia pallida, an important model system for coral symbiosis. Lipid extracts from A. pallida in and out of symbiosis with its symbiont Symbiodinium were prepared and analyzed using negative-ion electrospray ionization quadrupole time-of-flight mass spectrometry. Through this analysis we have identified, by exact mass and collision-induced dissociation mass spectrometry (MS/MS), several classes of glycerophospholipids in A. pallida. Several molecular species of di-acyl phosphatidylinositol and phosphatidylserine as well as 1-alkyl, 2-acyl phosphatidylethanolamine (PE) and phosphatidycholine were identified. The 1-alkyl, 2-acyl PEs are acid sensitive suggestive that they are plasmalogen PEs possessing a double bond at the 1-position of the alkyl linked chain. In addition, we identified several molecular species of phosphonosphingolipids called ceramide aminoethylphosphonates in anemone lipid extracts by the release of a characteristic negative product ion at m/z 124.014 during MS/MS analysis. Sulfoquinovosyldiacylglycerol (SQDG), an anionic lipid often found in photosynthetic organisms, was identified as a prominent component of Symbiodinium lipid extracts. A comparison of anemone lipid profiles revealed a subset of lipids that show dramatic differences in abundance when anemones are in the symbiotic state as compared to the non-symbiotic state. The data generated in this analysis will serve as a resource to further investigate the role of lipids in symbiosis between Symbiodinium and A. pallida.
Changing oceanic environmental factors disrupt the symbiotic relationship between cnidarians and a photosynthetic dinoflagellate symbiont, leading to expulsion of the symbiont from the cnidarian and endangering fragile coral ecosystems. The symbiosis between the anemone Aiptasia pallida and Symbiodinium is a model system for studying the molecular changes that occur during the establishment, maintenance and disruption of symbiosis. The symbiont resides in a specialized membrane component called the symbiosome membrane indicating dramatic changes to the lipidome of the anemone and symbiont. We have undertaken a comprehensive characterization of the lipid composition of the anemone, and symbiont at all stages of the symbiotic relationship. Lipids from the aposymbiotic symbiont, aposymbiotic anemone, and symbiotic anemone and symbiont were extracted and analyzed using liquid chromatography electrospray ionization mass spectrometry. Preliminary results based on exact mass and collision‐induced decomposition mass spectrometry reveal the presence of glycerophospholipids, phosphatidylethanolamine, phosphatidylserine, and phosphatidylcholine and interestingly, several molecular ions do not correspond to any known lipid molecular species. Lipidomic changes will be correlated to transcriptomic changes known to occur at the various stages of symbiosis.
Our research focuses on identifying lipids involved in the symbiosis between the anemone Aiptasia pallida and its photosynthetic dinoflagellate Symbiodinium. Liquid chromatography quadrupole time‐of‐flight mass spectrometry (MS) was used to analyze lipid extracts of aposymbiotic and holosymbiotic A. pallida and Symbiodinium. By comparing the intensity of each lipid (as defined by RT and m/z) between aposymbionts and holosymbionts, we observed lipidomic changes that occur when A. pallida and Symbiodinium enter symbiosis. The lipidome of A. pallida displays numerous changes as a result of symbiosis formation; [M‐H] − ions at m/z 765.4, 1033.5, and 1061.6 displayed >900‐fold increase in intensity. To begin to characterize these lipids, we partially purified via normal phase HPLC the lipid at m/z 765.4. Using collision induced dissociation MS and chemical modifications of functional groups we hypothesize that the lipid at m/z 765.4 is a diacyl‐glycerosulfolipid, with a head group attached to the sulfate with the formula C6H9O4. This work will lay the foundation for biochemical classification of all of the lipids in this systeme, and determination of what role they play in the symbiosis. This work was funded by a Cottrell College Science Award to J. Schwarz and E. Eberhardt and an ASBMB Undergraduate Affiliate Network Summer Research Award to J. Schmeitzel.
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