Melatonin disturbed rumen microflora structure and metabolic pathways in vitro

ABSTRACT Melatonin (MLT) can affect the microbial community structure and its metabolites by releasing cellular regulatory factors. Intestinal bacteria recognize and respond to MLT signals from the intestine through MLT binding sites and further activate the function of intestinal immune cells. However, the signal transduction pathway of MLT in the intestine has not been clearly elucidated yet. The effect of MLT on rumen bacterial metabolism was studied by simulating rumen fermentation in vitro. The test was divided into three groups: artificial saliva+standard MLT solution (CK0 group), artificial saliva+rumen juice (CK1 group), and artificial saliva+rumen juice+standard MLT solution (MLT group). The fermentation broth was collected after 24 h of simulated culture in vitro. The results showed that the addition of MLT significantly increased the contents of propionic acid, butyric acid, valeric acid, and total volatile fatty acids (P < 0.05). The analysis of the differences in flora found that at the genus level, Alistipes, Veillonellaceae_UCG-001, Selenomonas, Lachnospiraceae_NK4A136_group, and Succinivibrio were significantly increased, whereas Acinetobacter and Prevotella were significantly decreased (P < 0.05). The analysis of differential metabolites showed that compared with the CK1 group, the relative contents of glutathione, spermidine, indole, 3-methyl indole, phenylpyruvate, and other metabolites were increased significantly in the MLT group (P < 0.05). The results of enzyme activity on the enrichment pathway showed that MLT could significantly enhance the activities of genes such as GST, SPDS, DAHP, AS, TS, TPH, AANAT, ASMT, and IDO. Therefore, melatonin had certain regulatory effects on rumen microorganisms and their metabolic pathways. IMPORTANCE In in vitro studies, it has been found that the effects of MLT on rumen microorganisms and metabolites can change the rumen flora structure, significantly inhibit the relative abundance of harmful Acinetobacter, and improve the relative abundance of beneficial bacteria. MLT may regulate the “arginine-glutathione” pathway, “phenylalanine, tyrosine and tryptophan biosynthesis-tryptophan generation” branch, “tryptophan-kynurenine” metabolism, and “tryptophan-tryptamine-serotonin” pathway through microorganisms.