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.

In the rumen bacteria, ammonia as the end product of nitrogen is incorporated into carbon skeleton (α-ketoglutarate) to yield glutamine and glutamate which are important nitrogen donors in nitrogenous compounds metabolism in cells. The enzymes glutamine synthetase, glutamate synthetase, and glutamate dehydrogenase are involved in these processes. Some experimental results have proven that the global nitrogen regulation system may participate in the regulation of assimilation of ammonia in rumen bacteria. This review offers a current perspective on the pathways and key enzymes of ammonia assimilation in rumen bacteria with the possible molecular regulation strategy, while points out the further research direction.

Understanding of the colonization process of epithelial bacteria attached to the rumen tissue during rumen development is very limited. Ruminal epithelial bacterial colonization is of great significance for the relationship between the microbiota and the host and can influence the early development and health of the host. MiSeq sequencing of 16S rRNA genes and quantitative real-time PCR (qPCR) were applied to characterize ruminal epithelial bacterial diversity during rumen development in this study. Seventeen goat kids were selected to reflect the no-rumination (0 and 7 days), transition (28 and 42 days), and rumination (70 days) phases of animal development. Alpha diversity indices (operational taxonomic unit [OTU] numbers, Chao estimate, and Shannon index) increased ( P < 0.01) with age, and principal coordinate analysis (PCoA) revealed that the samples clustered together according to age group. Phylogenetic analysis revealed that Proteobacteria , Firmicutes , and Bacteroidetes were detected as the dominant phyla regardless of the age group, and the abundance of Proteobacteria declined quadratically with age ( P < 0.001), while the abundances of Bacteroidetes ( P = 0.088) and Firmicutes ( P = 0.009) increased with age. At the genus level, Escherichia (80.79%) dominated at day zero, while Prevotella , Butyrivibrio , and Campylobacter surged (linearly; P < 0.01) in abundance at 42 and 70 days. qPCR showed that the total copy number of epithelial bacteria increased linearly ( P = 0.013) with age. In addition, the abundances of the genera Butyrivibrio , Campylobacter , and Desulfobulbus were positively correlated with rumen weight, rumen papilla length, ruminal ammonia and total volatile fatty acid concentrations, and activities of carboxymethylcellulase (CMCase) and xylanase. Taking the data together, colonization by ruminal epithelial bacteria is age related (achieved at 2 months) and might participate in the anatomic and functional development of the rumen.

Background: Different carbohydrates ingested greatly influence rumen fermentation and microbiota and gaseous methane emissions. Dissolved hydrogen co

The effects of yeast culture and fibrolytic enzyme preparation (containing cellulase and xylanase) on in vitro fermentation characteristics of rice straw, wheat straw, maize stover, and maize stover silage were examined using an in vitro gas production technique. Four levels of yeast culture and fibrolytic enzyme supplements (0, 2.5, 5.0, and 7.5 g/kg of straw DM, respectively) were tested in a 4 × 4 factorial arrangement. Supplementation of yeast culture increased the cumulative gas production, theoretical maximum of gas production, rate of gas production, IVDMD, and in vitro OM disappearance (IVOMD), and decreased the lag time for each type of straw. Fibrolytic enzyme supplementation tended to increase cumulative gas production, theoretical maximum of gas production, and rate of gas production; prolonged lag time of gas production; and enhanced IVDMD and IVOMD for 4 types of cereal straws, with the significance of this effect being dependent on the level of supplemented enzymes. There were significant interactions between fibrolytic enzymes and yeast on all in vitro gas production parameters, IVDMD, and IVOMD of each type of straw. The outcome of this research indicated that the application of fibrolytic enzyme preparation and yeast culture could improve in vitro gas production fermentation of cereal straws. Copyright © 2008. . Copyright 2008 Journal of Animal Science

Dissolved hydrogen (dH₂) influences the pathways of VFA production and is a precursor of methane formation in the rumen. Measurements of dH₂ in rumen fluid taken at the same time as measuring other rumen fermentation end products would improve our quantitative understanding of the role of dH₂ as a controller of rumen fermentation. Sample collections though a rumen cannula and using oral stomach tubing were compared for measurements of dissolved gases and fermentation end products in the rumen fluid of 4 ruminally cannulated dairy cows fed a total mixed ration of corn silage and concentrate. Rumen fluid was collected at 0, 2.5, and 6 h after morning feeding through the cannula from cranial dorsal rumen, cranial ventral rumen, central rumen, caudal dorsal rumen, and caudal ventral rumen and in parallel by oral stomach tubing at 2 insertion depths of 180 cm (sampling the central rumen) and 200 cm (sampling the caudal dorsal rumen). The cranial dorsal rumen had the greatest pH and smallest VFA concentration among 5 sites sampled. Samples collected by oral stomach tubing had greater (P < 0.001) rumen pH and less (P < 0.001) dissolved methane (dCH₄) and lower VFA concentration than that collected through rumen cannula. The dH₂ concentrations were positively correlated (r > 0.8) in rumen samples collected by the 2 sampling techniques, with a concordance correlation coefficient larger than 0.8 and scale shift being about 0.1 away from unity. The variations in the measurement of dH₂, dCH₄, pH, and VFA in samples collected by oral stomach tubing are most likely the result of saliva contamination. The time of sampling relative to feeding had significant influence (P < 0.01) on dissolved gases and fermentation end products, with the greatest concentrations of dH₂, dCH₄, and VFA measured 2.5 h after morning feeding. The dH₂ was correlated positively (r > 0.58) with dCH₄ and negatively (r < −0.65) with the estimated net H₂ production relative to the amount of VFA produced. This indicated that greater dH₂ enhanced rumen CH₄ production and also led to fermentation pathways that produce less H₂, such as enhanced propionate and butyrate production. In summary, oral stomach tubing could be a feasible method to measure ruminal dH₂ in intact animals, but caution should be taken to minimize saliva contamination. Measurements made using both techniques yield similar conclusions for the effects of dH₂ on fermentation pathways and CH₄ generation.