Dietary methionine supplementation alters the expression of genes involved in methionine metabolism in salmonids

• We examine the expression of genes of methionine metabolism.
• We explore the significance of alternate feeding strategies for methionine.
• Dietary methionine affects expression of genes involved in net methionine loss.
• Dietary methionine level changes expression of genes of methionine re-synthesis.

The objective of the present study was to investigate the effect of dietary methionine (Met) concentration and alternating feeding strategies in methionine delivery, on the mRNA transcript levels of genes involved in Met resynthesis (betaine-homocysteine methyltransferase, BHMT; S-adenosylhomocysteine hydrolase, SAHH) and net Met loss (taurine synthesis) (cystathionine beta-synthase, CBS) in Atlantic salmon (Salmo salar) liver. Salmon alevins (265 ± 3 mg) were distributed into 24 tanks (50 fish per tank; 3 replicates). The experimental diets were supplemented with l-methionine at 0, 1.9, 5.8, and 17.4 g/kg (M0, M1/3, M1, and M3, respectively). The M3 diet without glycine was prepared to examine Met toxicity (M3-G). These diets were provided via “mono-feeding strategy,” meaning fish were fed a designated single diet. This experiment also included alternative feeding groups with “duo-feeding” strategy: AF1 (fish fed M0 for 2 days followed by M1 for 1 day), AF2 (fish fed M0 for 2 days followed by M3 for 1 day), and AF3 (fish fed two meals of M0 followed by one meal of M3). Salmon fed M0 diet had smaller weight compared to all other groups. There was no effect of alternative feeding on the growth except with the M0 group. The highest expression of CBS gene was found in the M0, M1/3, and AF-1 groups compared to the M3 and M3-G groups. The expression of CBS gene in the M1 group was lower compared to the AF-1 group. The expression of SAHH gene was the highest in the M3 group compared to the M1, M1/3, and AF-3 groups. The highest expression of BHMT gene was found in the M0, M1/3, and AF-1 groups, indicating enhanced re-methylation of homocysteine by betaine to Met. The lowest BHMT expression in M1, M3, M3-G, AF-2, and AF-3 groups compared to other treatments can be indicative of downregulation of remethylation in the liver. The alternate provision of methionine in a form of combination of low and high methionine containing diets seemed to support its efficient utilization in the salmon liver.