Rumen microbiota–host interactions regulate intramuscular fat deposition in cattle via the alpha-linolenic acid–fatty acid β-oxidation/L-carnitine–MPO axis

BACKGROUND: Beef, known for its high protein, low fat, and rich amino acid content, is a premium source of nutrition compared to other meats. As living standards improve, higher demands are being placed on beef quality, which is closely related to intramuscular fat (IMF) content. Jiaxian Red Cattle, a local Chinese breed, is renowned for its high meat quality, characterized by reddish muscle color and snow-white fat. However, the molecular mechanisms underlying differences in intramuscular fat deposition and meat quality in this breed remain unclear. This study aims to explore the potential molecular mechanisms of intramuscular fat deposition in beef cattle using multi-omics approaches. RESULTS: Non-targeted metabolomic analysis of rumen fluid identified α-linolenic acid as a key metabolite promoting fat accumulation. Four genera-Cnuella, Gaetbulibacter, Moheibacter, and Lacibacter-were significantly positively correlated with α-linolenic acid (r > 0.83, p < 0.05), highlighting their roles in shaping a metabolic environment conducive to intramuscular fat deposition. Pathway analysis revealed that in the high intramuscular fat group (group H-IMF), the fatty acid β-oxidation pathway was significantly inhibited, reducing fatty acid oxidation and promoting fat deposition. Additionally, metabolomic data from longissimus dorsi muscle tissue showed significantly lower levels of N,N,N-trimethyllysine, L-carnitine, and betaine in group H-IMF (p < 0.05). These metabolites were negatively correlated with Cnuella, Gaetbulibacter, Moheibacter, and Lacibacter, indicating a complex interplay between these microbiota and the metabolic network regulating intramuscular fat deposition. These metabolites also interacted with proteins like ACSS1, ACSF2, and MPO to modulate fat formation. In vitro experiments confirmed these findings: overexpression of the MPO gene significantly enhanced intramuscular fat accumulation (p < 0.05), while L-carnitine and betaine suppressed MPO expression (p < 0.05). CONCLUSIONS: This study reveals that Moheibacter, Cnuella, Gaetbulibacter, and Lacibacter play central regulatory roles in intramuscular fat deposition in beef cattle via the α-linolenic acid-fatty acid β-oxidation/L-carnitine-MPO axis. These findings highlight the critical role of microbial communities in regulating fat deposition through complex host-microbe interactions, providing insights for future strategies aimed at enhancing beef quality. Video Abstract.