Ruminants are important for global food security but emit the greenhouse gas methane. Rumen microorganisms break down complex carbohydrates to produce volatile fatty acids and molecular hydrogen. This hydrogen is mainly converted into methane by archaea, but can also be used by hydrogenotrophic acetogenic and respiratory bacteria to produce useful metabolites. A better mechanistic understanding is needed on how dietary carbohydrates influence hydrogen metabolism and methanogenesis. We profiled the composition, metabolic pathways, and activities of rumen microbiota in 24 beef cattle adapted to either fiber-rich or starch-rich diets. The fiber-rich diet selected for fibrolytic bacteria and methanogens resulting in increased fiber utilization, while the starch-rich diet selected for amylolytic bacteria and lactate utilizers, allowing the maintenance of a healthy rumen and decreasing methane production (p < 0.05). Furthermore, the fiber-rich diet enriched for hydrogenotrophic methanogens and acetogens leading to increased electron-bifurcating [FeFe]-hydrogenases, methanogenic [NiFe]- and [Fe]-hydrogenases and acetyl-CoA synthase, with lower dissolved hydrogen (42%, p < 0.001). In contrast, the starch-rich diet enriched for respiratory hydrogenotrophs with greater hydrogen-producing group B [FeFe]-hydrogenases and respiratory group 1d [NiFe]-hydrogenases. Parallel in vitro experiments showed that the fiber-rich selected microbiome enhanced acetate and butyrate production while decreasing methane production (p < 0.05), suggesting that the enriched hydrogenotrophic acetogens converted some hydrogen that would otherwise be used by methanogenesis. These insights into hydrogen metabolism and methanogenesis improve understanding of energy harvesting strategies, healthy rumen maintenance, and methane mitigation in ruminants.

反刍动物对全球粮食安全很重要，但会排放温室气体甲烷。瘤胃微生物分解复杂的碳水化合物以产生挥发性脂肪酸和分子氢。这种氢主要被古细菌转化为甲烷，但也可以被氢营养型产乙酸细菌和呼吸细菌用来产生有用的代谢物。需要更好地了解膳食碳水化合物如何影响氢代谢和产甲烷作用。我们分析了 24 头适应富含纤维或富含淀粉饮食的肉牛的瘤胃微生物群的组成、代谢途径和活动。为纤维分解细菌和产甲烷菌选择富含纤维的饮食导致纤维利用增加，而为淀粉分解细菌和乳酸利用者选择富含淀粉的饮食，p  < 0.05)。此外，富含氢营养产甲烷菌和产乙酸菌的富含纤维的饮食导致电子分叉[FeFe]-氢化酶、产甲烷[NiFe]-和[Fe]-氢化酶以及乙酰辅酶A合酶增加，溶解氢较低（42%，p  < 0.001)。相比之下，富含淀粉的饮食富含呼吸氢营养菌，具有更大的产氢组 B [FeFe]-氢化酶和呼吸组 1d [NiFe]-氢化酶。平行的体外实验表明，富含纤维的选定微生物组增强了乙酸盐和丁酸盐的产生，同时降低了甲烷的产生（p < 0.05），表明富氢营养产乙酸菌转化了一些氢气，否则这些氢气将被产甲烷所使用。这些对氢代谢和甲烷生成的见解提高了对反刍动物能量收集策略、健康瘤胃维持和甲烷缓解的理解。