Abundance distribution of Quinella bacteria in the rumen of highland yaks and its effects on ruminal carbohydrate metabolism

Abstract This study aimed to investigate the abundance distribution of Quinella in yak rumen, a dominant microbe associated with low methane emissions and high propionate yield, and its modulation of microbial carbohydrate metabolism. A high-quality genomic database for rumen Quinella was constructed through the screening of 12 717 published metagenome-assembled genomes from 12 ruminant species. Genomic annotation indicated that Quinella possessed two distinct gene clusters for converting fumarate to propionate. The 16S rRNA sequencing data revealed that the ruminal Quinella abundance is host-dependent, with a markedly higher prevalence in yaks (56.3%) than in cattle (3.01%). In yaks, higher rumen Quinella abundance was accompanied by the lower abundances of enoyl-CoA hydratase and acetate CoA transferase, encoding two butyrate synthetases but higher abundances of key genes involved in propionate synthesis. In vivo analyses found that yaks carrying more Quinella abundance (high or low groups, n = 9 per group) exhibited higher total volatile fatty acids and lower butyrate percentage in their ruminal contents. Additionally, comparative metagenomic analysis indicated that microbial genes from yaks with higher Quinella were enriched in critical metabolic pathways, including glycolysis, the reductive Krebs cycle, and the conversion of acetyl-CoA to acetate. However, no significant differences in methane production (prediction based) were observed between yaks with higher or lower Quinella ( n = 9 per group). In summary, this study provided a valuable genomic resource for further research on Quinella and partially verified its potential in microbial carbohydrate metabolism, specifically enhancing volatile fatty acid production. However, its role in yak methane emission requires further validation.