Distinct microbial hydrogen and reductant disposal pathways explain interbreed variations in ruminant methane yield

Area of Science:

• Rumen microbiology and biochemistry
• Greenhouse gas mitigation in livestock

Background:

• Ruminants are vital for food security but significant methane emitters.
• Methane production is linked to hydrogen (H2) cycling in the rumen.
• Understanding H2 metabolism variations in different ruminant phenotypes is crucial.

Purpose of the Study:

• To compare H2 cycling and reductant disposal pathways in low- vs. high-methane-emitting dairy cattle.
• To identify microbial mediators and metabolic pathways influencing methane yield.

Main Methods:

• Utilized metagenomics, metatranscriptomics, metabolomics, and biochemical analyses.
• Compared rumen microbiomes of Holstein (low-methane) and Jersey (high-methane) cattle.
• Included in vitro measurements and analysis of global microbiome data.

Main Results:

• Holstein cattle showed enhanced reductant disposal via amino acid synthesis and propionate production, using H2 for sulfate/nitrate respiration, reducing methane.
• Jersey cattle exhibited greater H2 production via fermentative hydrogenases, with H2 primarily used for methanogenesis and acetogenesis, increasing methane.
• Alternative H2 consumption pathways correlate with reduced methane emission and increased host-beneficial metabolite synthesis.

Conclusions:

• Rumen microbial H2 metabolism significantly influences methane emissions in ruminants.
• Targeting alternative H2 consumption pathways can mitigate methane production.
• Promoting pathways for synthesizing host-beneficial metabolites offers a strategy to reduce ruminant methane.