Genomic insights into the physiology of <i>Quinella</i>, an iconic uncultured rumen bacterium

<i>Quinella</i> is a genus of iconic rumen bacteria first reported in 1913. There are no cultures of these bacteria, and information on their physiology is scarce and contradictory. Increased abundance of <i>Quinella</i> was previously found in the rumens of some sheep that emit low amounts of methane (CH₄) relative to their feed intake, but whether <i>Quinella</i> contributes to low CH₄ emissions is not known. Here, we concentrate <i>Quinella</i> cells from sheep rumen contents, extract and sequence DNA, and reconstruct <i>Quinella</i> genomes that are &gt;90% complete with as little as 0.20% contamination. Bioinformatic analyses of the encoded proteins indicate that lactate and propionate formation are major fermentation pathways. The presence of a gene encoding a potential uptake hydrogenase suggests that <i>Quinella</i> might be able to use free hydrogen (H₂). None of the inferred metabolic pathways is predicted to produce H₂, a major precursor of CH₄, which is consistent with the lower CH₄ emissions from those sheep with high abundances of this bacterium.