摘要Background The ketogenic diet that forces adenosine triphosphate(ATP)production by beta-oxidation of fatty acids instead of carbohydrate glycolysis,has gained consensus on host metabolism.However,the mechanisms how a ketogenic diet alters gastrointestinal microbiome and its downstream consequences on microbial nutrient availability and energy metabolism remain to be elucidated.Here,we used the sheep model fed with fat-rich diet to evaluate the symbiotic microbiome across three regions of the gastrointestinal tract(rumen,ileum,and colon)to gain a comprehensive understanding of the microbial energy metabolism and microbe-mediated ATP biosynthesis.Results Results showed that sheep fed a fat-rich diet had a greater ADG and increased reliance on fat oxida-tion for fuel utilization.Metagenomics analysis showed the loss of the specialized fiber-degrading bacteria(genus_Fibrobacter)in the rumen and enrichment of genera RUG420 and Eubacterium,which are involved in lipid metabolism and bile acid processing,in the ileum.A significant functional shift related to energy metabolism was shared across three regions of the gastrointestinal microbiomes.These shifts were dominated by glycolysis/glu-coneogenesis and TCA cycle in the rumen and by fatty acid degradation and bile acid transformation in the ileum,indicating adaptation to nutrient availability and energy acquisition.Notably,the abundance of substrate-level phosphorylation(SLP)enzymes was significantly increased in the rumen,ileum and colon,while the ATP-producing capacity through electron transport phosphorylation(ETP)by family_Bacteroidaceae in rumen and Acutalibacte-raceae in ileum of sheep with fat-rich diet.Conclusions Altogether,the ATP-related microbiome encoding SLP and ETP in rumen,ileum,and colon contributed 36.95％to the host's weight variation.Our study is the first one demonstrating the microbial potential in the ATP synthesis under the shift in dietary energy source,providing a new perspective on the energy metabolism and precise human macronutrients nutrition.