Fatty acid composition of symbiotic zooxanthellae in relation to their hosts

Abstract

Gymnodinoid dinoflagellate symbionts, commonly referred to as zooxanthellae, are widely distributed among marine invertebrates. It has been assumed that they represent only one species,Gymnodinium microadriaticum. The fatty acid composition of total lipids and galactolipids of zooxanthellae isolated from 8 species of corals, 3 species of clams and a foraminiferan have been analyzed and found to vary according to the host. For example, the content of eicosapentaenoic acid in clam zooxanthellae monogalactosyldiacylglycerol was less than 2%, whereas in the same lipid from coral zooxanthellae, the content ranged from 9 to 22%. Corresponding values for the acid in digalactosyl-diacylglycerol were 1-8% from clam zooxanthellae and 23-40% from coral zooxanthellae. Coral zooxanthellae monogalactosyldiacylglycerol contain higher levels of octadecatetraenoic acid than are found in digalactosyldiacylglycerol, whereas the reverse is true in clam zooxanthellae. The fatty acid composition of the lipids of an axenic culture of zooxanthellae isolated from the clamTridacna maxima are similar to those of cells freshly isolated from the host. The results suggest either that the host is capable of affecting the fatty acid metabolism of the symbiont or that different strains of zooxanthellae occur in corals and clams.

Fatty Acid Biomarkers of Symbionts and Unusual Inhibition of Tetracosapolyenoic Acid Biosynthesis in Corals (Octocorallia)

“…Another way of the influence on the FA composition of a whole colony consists in the transfer (and possible accumulation) of FA synthesized by zooxanthellae to the coral host [10,12]. For reef-building corals, the transfer of saturated FA have been shown; the transfer of some PUFA have been supposed [9,11,13,25], but the mechanism of this process is under discussion [50]. We described earlier for alcyonarians the significant excess of saturated FA in zooxanthellate species compared to species without zooxanthellae [24].…”

“…Studies of FA in soft corals have not so far been systematic, and data on the FA contents of total lipids of the corals, especially of gorgonian corals, are limited [17][18][19][20][21][22][23][24]. Only a few works describe the FA of symbiotic dinoflagellates of the reef-building corals [8,11,13,25]. Data on the FA composition of zooxanthellae from soft corals have not been available until now.…”

Fatty acids of reef-building corals

“…High levels of 18:3(n-6) and 20:3(n-6) acids were characteristic of all the examined Anthozoa (except the non-zooxanthellate Dendrophyllidae). Zooxanthellae are their probable source, as it was earlier shown that zooxanthellae glycolipids contained 18:3(n-6) acid as the main component (Bishop & Kenrick 1980). Corals without zooxanthellae have low contents of polyenoic C18 and 20:3(n-6) acids, but high levels of 18:l(n-9) and 22:5(n-3) acids are characteristic for them.…”

Distribution of lipids and fatty acids in corals by their taxonomic position and presence of zooxanthellae

“…FAs are most probably indicative of external food sources (Dalsgaard et al 2003). In addition, zooxanthellae have an FA composition different from that of external food sources (Bishop & Kenrick 1980, Zhukova & Titlyanov 2003, The transport of FA from zooxanthellae to the host has been documented (Harland et al 1993, Al Moghrabi et al 1995, Ward 1995, Papina et al 2003. Therefore, the absence of symbiotic dinoflagellates in corals should lead to a significant difference in lipid and FA compositions between zooxanthellate and azooxanthellate coral species (Imbs et al 2007b).…”