Can Artemia produce essential fatty acids? Roles of elongases in the biosynthesis of long-chain polyunsaturated fatty acids?

Póster presentado en la International Conference & Exposition Aquaculture Europe, celebrada en Funchal, Maderia (Portugal) del 04 al 07 de octubre de 2021.[Introduction]: Artemia nauplii are one of the most commonly used live preys in marine larviculture. However, a major drawback associated to using Artemia nauplii is their deficient nutritional value for marine fish larvae that is primarily linked to suboptimal levels of long-chain (C20-24) polyunsaturated fatty acids (LC-PUFA). LC-PUFA including eicosapentaenoic acid (EPA, 20:5n-3), arachidonic acid (ARA, 20:4n-6) and docosahexaenoic acid (DHA, 22:6n-3) are essential compounds for normal development of vertebrates including fish. Since Artemia contains low LC-PUFA, with only trace levels of DHA, nauplii must be enriched with LC-PUFA-rich products prior use as live prey for marine larvae. However, it remains unknown whether Artemia has some capacity for LC-PUFA biosynthesis itself. Elongases (Elo) are key enzymes in the LC-PUFA biosynthetic pathway that catalyse the limiting step reaction in the fatty acid (FA) elongation pathway resulting in a 2-carbon extension of the FA substrate. In the present study, we aimed to clarify the repertoire and function of Elo with putative roles in the LC-PUFA biosynthesis of Artemia franciscana, arguably the most commonly used Artemia species in aquaculture. [Results]: Six elongases, termed Elo1 to Elo6, were identified, cloned and characterised. Identified enzymes contained the motif [(Q/H)(V/I/L)(S/T)(F/L/V)LH(V/I/L)(Y/V/I)HH] and six transmembrane spanning regions. The ability of the A. franciscana Elo enzymes to elongate PUFA substrates was assayed in yeast. The capacity of the A. franciscana Elo to elongate the exogenously supplemented PUFA varied among enzymes. Both Elo2 and Elo5 were able to convert all PUFA assayed (18:3n-3, 18:2n-6, 18:4n-3, 18:3n-6, 20:5n-3, 20:4n-6, 22:5n3 and 22:4n-6) to the corresponding 2-carbon elongated products. Moreover, both Elo1 and Elo6 had the ability to elongate all C18 PUFA substrates, as well as 20:5n-3, although Elo1 but not Elo6 elongated 22:5n-3 to 24:5n-3. Finally, the A. franciscana Elo3 and Elo4 recognised only two out of four C18 PUFA as substrates, namely 18:4n-3 and 18:3n-6 for Elo3, and 18:2n-6 and 18:3n-6 for Elo4, with no activity detected towards any C20 and C22 PUFA. [Discussion and conclusions]: PUFA elongases have been found and characterised in several invertebrates including crustaceans. The A. franciscana Elo genes share the motif [(Q/H)(V/I/L)(S/T)(F/L/V)LH(V/I/L)(Y/V/I)HH], which is characteristic from PUFA elongases. The A. franciscana Elo1 can be classified in the group of Elovl4, an Elo type that is widespread in animals including the branchiopod crustacean Daphnia magna. Interestingly, the A. franciscana Elo2-6 belong to a group of unclassified elongases arbitrarily named ¿novel¿ elonganses, which have been found extensively in crustaceans such as the marine gammarid Echinogammarus marinus. Our functional data clearly show that the A. franciscana Elo1-6 can catalyse all the elongation reactions involved in the LC-PUFA biosynthetic pathways and, while further studies are required to clarify the presence of fatty acyl desaturases, we can conclude that Artemia has some capacity for biosynthesis of essential FA. required to clarify the presence of fatty acyl desaturases, we can conclude that Artemia has some capacity for biosynthesis of essential FA