RNA sequencing revealed similar reduction in muscular gene expression profiles of methyltrasferases when fed methionine enriched diets supplemented with either threonine, lysine and taurine or cobalamine, pyridoxine and folate during the freshwater p

Pre-smolts of Atlantic salmon were fed diets added either the valuable amino acids (AA diet) methionine, taurine, lysine and threonine and compared to fish fed a B-vitamin diet (B-vit diet) added methionine as well as the selected B-vitamins, folic acid (vitamin B9), cobalamin (vitamin B12) and pyridoxin (vitamin B6) all of which are important 1-carbon nutrients (1C nutrients). Both of these diets were compared to a control diet not added surplus AA or 1C nutrients. All diets were fed to triplicate tanks for a period of 42 days. There were no differences in either growth or protein utilization between any of the treatments, however, the free amino acids and N-metabolites showed reduction in liver (22/28) and increased levels in muscle (10/31) in both AA and B-vit fed fish. Muscle 5Me-THF and cystathionine utilized for re-methylation and transsulfuration of homocysteine in the methionine cycle, respectively, was reduced in both supplemented diets compared to control fish, but the reduction was not significant for 5Me-THF when fed the AA diet. RNA sequencing of white muscle revealed similar alterations of active metabolic pathways when fed either the AA or B-vit diets when comparing with fish fed the control diet. We found about equal numbers of differentially expressed genes (DEGs) between the control and AA fed fish (49 DEGs, 45 down- and 4 upregulated) and between the control and B-vitamin fed fish (50 DEGs, 40 down- and 10 upregulated). Only 5 DEGs were identified when comparing the AA and B-vitamin fed fish. Interestingly, for both the amino acid and B-vitamin fed fish we found downregulation of the transferases phosphoethanolamine methyltransferase (pmt), phosphomethylethanolamine N- methyltransferase-like (nmt2) and methionine adenosyltransferase II, alpha a (mat2aa) all of which encodes proteins that utilize the downstream metabolite of methionine, S- adenosylmethionine, as a methyl donor. Altogether, when comparing the data from both liver and muscle, adding extra methionine with either additional selected AA or B-vitamins increase the capacity of the methionine cycle which increase the methylation capacity, reduces the transcription of transferases and can utilize more of the free amino acids to build new proteins suggesting that a prolonged feeding trial might led to better growth or better smoltification capacity.