Viral metagenomic analysis of fecal samples from Bos grunniens on the Qinghai-Tibet Plateau reveals novel picornaviruses and diverse CRESS-DNA viruses.

Introduction: The Qinghai-Tibet Plateau (QTP), one of the most extreme environments on Earth, provides a unique natural setting for exploring viral diversity and evolution under conditions of high altitude, hypoxia, and intense ultraviolet radiation. The yak (Bos grunniens), a key endemic ruminant species of the QTP, plays an essential ecological and economic role, yet its fecal virome remains poorly characterized. Methods: In this study, we analyzed 43 yak fecal samples collected from Yushu, Qinghai Province, and constructed nine metagenomic libraries to investigate the composition, diversity, and phylogenetic characteristics of the yak fecal virome. Results: Metagenomic sequencing generated approximately 463 million raw reads, of which 2.87 million were classified as viral. The viral reads in the sequenced libraries were primarily composed of single-stranded DNA viruses (92.46%), particularly members of Smacoviridae, Circoviridae, and Genomoviridae, whereas RNA viruses such as Picornaviridae accounted for a minor fraction (0.71%). Phylogenetic analyses revealed that several circular single-stranded DNA (CRESS-DNA) virus and picornavirus genomes share high similarity with known ruminant-associated viruses, while forming independent evolutionary clades, suggesting potential cross-species transmission among plateau animals. The large-scale divergence within Smacoviridae further reflects extensive lineage expansion under the plateau's extreme environmental pressures. Discussion: Compared with our previous yak virome study, this work provides independent and complementary insights into the genomic and evolutionary characteristics of key viral taxa. Overall, our findings expand the genomic landscape of the yak fecal virome and highlight the Qinghai-Tibet Plateau as an important reservoir for exploring viral diversity, evolution, and host-environment interactions in extreme ecosystems.