Correction: Boland, T.M.; et al. Feed Intake, Methane Emissions, Milk Production and Rumen Methanogen Populations of Grazing Dairy Cows Supplemented with Various C 18 Fatty Acid Sources. Animals 2020, 10, 2380

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Functional Prediction and Assignment of Methanobrevibacter ruminantium M1 Operome Using a Combined Bioinformatics Approach

Methanobrevibacter ruminantium M1 (MRU) is a rod-shaped rumen methanogen with the ability to use H2 and CO2, and formate as substrates for methane formation in the ruminants. Enteric methane emitted from this organism can also be influential to the loss of dietary energy in ruminants and humans. To date, there is no successful technology to reduce methane due to a lack of knowledge on its molecular machinery and 73% conserved hypothetical proteins (HPs; operome) whose functions are still not ascertained perceptively. To address this issue, we have predicted and assigned a precise function to HPs and categorize them as metabolic enzymes, binding proteins, and transport proteins using a combined bioinformatics approach. The results of our study show that 257 (34%) HPs have well-defined functions and contributed essential roles in its growth physiology and host adaptation. The genome-neighborhood analysis identified 6 operon-like clusters such as hsp, TRAM, dsr, cbs and cas, which are responsible for protein folding, sudden heat-shock, host defense, and protection against the toxicities in the rumen. The functions predicted from MRU operome comprised of 96 metabolic enzymes with 17 metabolic subsystems, 31 transcriptional regulators, 23 transport, and 11 binding proteins. Functional annotation of its operome is thus more imperative to unravel the molecular and cellular machinery at the systems-level. The functional assignment of its operome would advance strategies to develop new anti-methanogenic targets to mitigate methane production. Hence, our approach provides new insight into the understanding of its growth physiology and lifestyle in the ruminants and also to reduce anthropogenic greenhouse gas emissions worldwide.

Feed Intake, Methane Emissions, Milk Production and Rumen Methanogen Populations of Grazing Dairy Cows Supplemented with Various C 18 Fatty Acid Sources

Emissions of methane (CH4) from dairy production systems are environmentally detrimental and represent an energy cost to the cow. This study evaluated the effect of varying C18 fatty acid sources on CH4 emissions, milk production and rumen methanogen populations in grazing lactating dairy cows. Forty-five Holstein Friesian cows were randomly allocated to one of three treatments (n = 15). Cows were offered 15 kg dry matter (DM)/d of grazed pasture plus supplementary concentrates (4 kg DM/d) containing either stearic acid (SA), linseed oil (LO), or soy oil (SO). Cows offered LO and SO had lower pasture DM intake (DMI) than those offered SA (11.3, 11.5 vs. 12.6 kg/d). Cows offered LO and SO had higher milk yield (21.0, 21.3 vs. 19.7 kg/d) and milk protein yield (0.74, 0.73 vs. 0.67 kg/d) than those offered SA. Emissions of CH4 (245 vs. 293, 289 g/d, 12.4 vs. 15.7, 14.8 g/kg of milk and 165 vs. 207, 195 g/kg of milk solids) were lower for cows offered LO than those offered SA or SO. Methanobrevibacter ruminantium abundance was reduced in cows offered LO compared to SA. Offering supplementary concentrates containing LO can reduce enteric CH4 emissions from pasture fed dairy cows.

New Insight Into Rumen Methanogen Function: a Barrier Blocking Trimethylamine From Entering the Host Body

Background: Trimethylamine (TMA) is the precursor of trimethylamine N-oxide (TMAO), which has been known to promote human cardiovascular disease. Methanomassiliicoccales (Mmc), TMA-utilizing methanogens, may function as a TMA barrier for the host in the rumen. This study aimed to investigate the role of Mmc in rumen TMA elimination and the effect of choline addition in the diet on the rumen TMA and TMAO concentrations in the plasma and milk of dairy cows.Results: Three experiments, 2 rumen in vitro fermentation trials and 1 dairy cow in vivo trial, were conducted. Four groups were set in Experiment 1: control, nitroglycerin (NG, a methanogen inhibitor), TMA (0.69 mg/mL), and TMA + NG. The methanogenic activity was completely inhibited in the NG group, and no methane production was observed in the NG and TMA + NG groups. The TMA content hardly reduced in the TMA + NG group (0.66 mg/mL) after 2 d of incubation; in contrast, it reduced by 47.2% in the TMA group. Methanogen 16S rRNA gene sequencing showed that the relative abundance of Mmc increased in the TMA group (P = 0.005), which was confirmed by real-time polymerase chain reaction testing. Two taxa (Group 9 sp. ISO4-G1 and Group 10 sp.) at the species level mainly contributed to the increase in the relative abundance of Mmc. Four groups were set in Experiment 2: control, NG, choline (choline chloride, 1.0 mg/mL), and choline + NG. Choline was completely degraded in 24 h, and the TMA content reached the peak point in the fermentation culture. The TMA content in the choline + NG group did not reduce after the occurrence of the peak point. In contrast, the TMA content in the choline group started to decrease after 24 h, corresponding to the rapid increase in methane production. Eight mid-lactating, rumen-fistulated Holstein cows were randomly assigned to the control (n = 4) or choline (n = 4) group in Experiment 3: In the choline group, the cows were gradually supplemented with 100–250 g/(cow·d) of choline chloride over 4 weeks. In the choline group, TMA accumulated in the rumen fluid, and the abundance of Mmc 16S rRNA gene and choline-degrading bacterial cutC gene increased in the rumen content (P < 0.050). The TMAO content in the plasma and milk of the dairy cows was approximately 10 times higher in the choline group than in the control at day 28.Conclusion: Rumen Mmc functioned as a TMA barrier for the host. The increase in dietary choline caused more TMA to enter the host body, resulting in higher TMAO deposition in the milk of the dairy cows. It should be noted that TMAO-rich milk might degrade food safety. Moreover, it should be discreet to mitigate rumen methane emission by inhibiting the rumen methanogen activities, which might destroy the rumen TMA barrier.

Draft Genome Sequence of the Rumen Methanogen Methanobrevibacter olleyae YLM1

Methanobrevibacter olleyae YLM1 is a hydrogenotrophic methanogen, isolated from the rumen of a lamb. Its genome has been sequenced to provide information on the genomic diversity of rumen methanogens and support the development of approaches to reduce methane formation by ruminants.