# Salvianolic acid C inhibits methane emissions in dairy cows by targeting MCR and reshaping the rumen microbial community

## TL;DR

Salvianolic acid C, a plant compound, reduces methane emissions in cows by inhibiting a key enzyme and changing gut microbes.

## Contribution

Salvianolic acid C is identified as a plant-derived methane inhibitor targeting MCR and altering rumen microbiota.

## Key findings

- Salvianolic acid C binds strongly to MCR's active site with a binding energy of −8.2 kcal/mol.
- SAC supplementation reduced methane production in vitro without affecting fermentation parameters.
- SAC decreased Methanobrevibacter abundance and downregulated methanogenesis-related genes.

## Abstract

Methane (CH4) emissions from ruminants significantly contribute to greenhouse gas effects and energy loss in livestock production. Methyl-coenzyme M reductase (MCR) is the key enzyme in methanogenesis, making it a promising target for CH4 mitigation. This study aimed to identify and validate plant-derived inhibitors by using molecular docking to screen compounds with strong binding affinity to the F430 active site of MCR and assessing their efficacy in reducing CH4 emissions.

Molecular docking analysis identified salvianolic acid C (SAC) as a potent inhibitor of MCR, showing a strong binding affinity to the F430 active site (binding energy: −8.2 kcal/mol). Enzymatic inhibition assays confirmed its inhibitory effect, with a half-maximal inhibitory concentration (IC50) of 692.3 µmol/L. In vitro rumen fermentation experiments demonstrated that SAC supplementation (1.5 mg/g DM) significantly reduced CH4 production (P < 0.01) without negatively affecting major fermentation parameters. Microbial community analysis using 16S rRNA sequencing and metagenomics revealed that SAC selectively altered the rumen microbiota, increasing the relative abundance of Bacteroidota while significantly reducing Methanobrevibacter (P = 0.04). Moreover, metagenomic analysis showed the downregulation of key methanogenesis-related genes (mcrA and rnfC), suggesting a dual mechanism involving direct enzymatic inhibition and microbial community modulation.

These findings indicate that SAC effectively reduces CH4 production by inhibiting MCR activity and reshaping the rumen microbial community. As a plant-derived compound with strong inhibitory effects on methanogenesis, SAC presents a promising and sustainable alternative to synthetic CH4 inhibitors, offering potential applications for mitigating CH4 emissions in livestock production.