Date Published: April 29, 2019
Publisher: Public Library of Science
Author(s): Andrey B. Imbs, Ly P. T. Dang, Kien B. Nguyen, Timothy James Garrett.
To expand our knowledge of lipid and fatty acid (FA) biosynthesis in marine cnidarians, polar lipidomes of hydrocorals were studied for the first time and then compared with those of soft corals from tropical and boreal regions. The structure and content of FAs and molecular species of ethanolamine, choline, serine, and inositol glycerophospholipids (PE, PC, PS, and PI, respectively), and ceramide aminoethylphosphonate (CAEP) in tropical hydrocorals (Millepora platyphylla, M. dichotoma) and the cold-water hydrocoral Allopora steinegeri were determined by chromatography and mass spectrometry. All soft corals and cold-water hydrocorals are characterized by a considerable amount of C20 polyunsaturated FAs (PUFAs) elongated into C22 PUFAs. In the Millepora species, the high level of 22:5n-6 and 22:6n-3 against the background of the extremely low level of C20 PUFAs may be explained by a high activity of rare Δ4 desaturase. In contrast to hydrocorals, soft corals are able to elongate and further desaturate C22 PUFAs into C24 PUFAs. Allopora and soft corals use C20 PUFAs mainly for the synthesis of PE and PC. The molecular species of PS of soft corals concentrate C24 PUFAs, while in Allopora and Millepora the PS molecules are mainly based on 22:4n-6 and 22:5n-6 acyl groups, respectively. Short acyl groups (C14) dominate the CAEP molecules of Allopora. In all the animals compared, most molecular species of PE and PC are ether lipids, but diacyl molecular species dominate PI. Hydrocorals and tropical soft corals contain diacyl and ether PS molecules, respectively, whereas cold-water soft corals contain a mixture of these PS forms. The high similarity of the alkyl/acyl compositions indicates a possible biosynthetic relationship between PS and PI in hydrocorals. The data obtained in our study will provide a resource to further investigate the lipid metabolism in marine invertebrates.
Corals occur at depths of up to 6 km from polar to tropical waters of the World Ocean. Hard (or reef-building) corals, which have a hard exoskeleton, and soft corals are widely distributed in the tropical zones . Hydrocorals are also members of tropical coral reef ecosystems . For example, “fire coral” Millepora platyphylla, is an important component of Indo-Pacific reefs . Hard and soft corals belong to the class Anthozoa (the phylum Cnidaria). Hydrocorals resemble hard corals in appearance but belong to the class Hydrozoa . In tropical regions, most shallow-water hard and soft corals species, as well as Millepora, contain endocellular symbiotic dinoflagellates (SDs, microalgae of the family Symbiodiniaceae) referred to as zooxanthellae . SDs are an essential source of photosynthetic organic carbon for their host [6,7]. Many species of hard corals, soft corals, and hydrocorals inhabit the deep-sea and cold-water zones [8,9], but all these cnidarian species do not contain SDs. In warm and cold waters, corals and hydrocorals are an integral part of benthic communities with very high biodiversity [1,10].