Metagenomic and metatranscriptomic analysis reveals the enzymatic mechanism of plant polysaccharide degradation through gut microbiome in plateau model animal (Ochotona curzoniae).

Herbivorous animals can obtain energy by decomposing plant polysaccharides through gut microbiota, but the mechanism of gut microbiota decomposing plant polysaccharides in high-altitude model animals is still unclear. Plateau pika (Ochotona curzoniae) is a key model animal native to the Qinghai-Tibet Plateau with a high intake of grass. Thus, Plateau pika is an excellent animal model for studying how herbivorous animals digest and metabolize grass polysaccharides. Here, we used 16S rDNA, 16S rRNA, metagenomic, and metatranscriptomic sequencing to characterize gut microbial composition, gene potential, and expressed function in pikas from different altitudes. Unlike total bacteria, Oscillospira and Ruminococcus were main active bacterial genera in pika's gut. The metabolic pathways of cellulose and hemicellulose were up-regulated in the middle and high-altitude groups; those genes encoding polysaccharide enzymes were enriched. Notably, the proportion of lignin metabolic genes expressed in pika's gut was the highest, followed by cellulase and hemicellulase genes. According to comparative metagenomics of different animals, the number and relative abundance of cellulase and hemicellulase genes in pika's gut were at a higher level compared with steer, etc. These results indicated that plateau pika obtained sufficient energy from grass-based diet by increasing the expression of related metabolic enzymes.