Nutritional regulation of LC-PUFA biosynthesis in the marine polychaete Platynereis dumerilii.

Long-chain polyunsaturated fatty acids (LC-PUFA) are essential nutrients for membrane function, development, and immunity in animals. Polychaetes are promising sources of LC-PUFA due to their endogenous biosynthetic capacity, but optimal feeding strategies to enhance their nutritional value remain poorly understood. We investigated the nutritional regulation of LC-PUFA biosynthesis in the marine polychaete Platynereis dumerilii fed three diets differing in fatty acid (FA) profiles: spinach, yeast, and commercial fish feed. Juveniles were cultured for 37 days at 35‰ salinity, and survival, growth, total lipids, FA profiles, and expression of elongases, desaturases, and putative transcription factors were analysed. Survival rates were high across all diets (93.3-95.0%), while growth was significantly reduced in spinach-fed worms, which showed a lower specific growth rate (1.5 ± 0.1% day-1) than worms fed yeast (2.2 ± 0.1% day-1) or fish feed (2.0 ± 0.1% day-1). Diet strongly affected FA composition: fish feed increased n-3 LC-PUFA, spinach elevated α-linolenic acid, and yeast enhanced n-6 LC-PUFA. Despite low dietary LC-PUFA, eicosapentaenoic acid levels remained stable, indicating active endogenous synthesis. Gene expression responses were diet-dependent, with elongase Elovl2/5 expression higher in fish-feed-fed worms (0.8 ± 0.3) than in yeast-fed worms (0.4 ± 0.1), while the front-end desaturase Fed1 (Δ5 activity) and methyl-end desaturase ω des1 (Δ12 activity) showed their highest expression in spinach-fed worms (3.9 ± 1.8 and 2.4 ± 1.0, respectively). Overall, P. dumerilii adjusted its lipid metabolism in response to dietary inputs, demonstrating transcriptional plasticity and reinforcing its potential as a sustainable source of LC-PUFA.