Metagenomic analysis of the DNA virome communities in swine lungs

Viruses play critical roles in shaping microbial communities and regulating host metabolism. Investigating the lung virome of pigs can inform swine health management and provide a comparative resource for studies of the human lower respiratory virome. However, viral communities in the porcine lower respiratory tract remain poorly characterized. In this study, lung-associated viral communities were investigated using virus-like particle (VLP) enrichment and DNA metagenomic sequencing of 49 lung-derived samples collected from 17 domestic pigs and 20 wild boars. A total of 18,412 viral operational taxonomic units (vOTUs) were identified. Among the 2,559 vOTUs with genome completeness ≥50%, nearly 95% did not cluster with sequences in current viral reference databases at the species-level threshold (ANI ≥ 95% and AF ≥ 85%), suggesting putative viral novelty in the porcine lung while also reflecting incomplete reference database coverage. Meanwhile, 10,819 vOTUs (accounting for 58.8% of the total 18,412 identified vOTUs) were assigned to known viral taxa, spanning 29 viral orders and 65 viral families. The most prevalent viral families were Microviridae, Circoviridae, Smacoviridae, Adintoviridae, and Autographiviridae. Host prediction linked a subset of vOTUs to putative bacterial hosts, mainly from Pseudomonadota, Bacillota, Bacteroidota and Actinomycetota. In addition, we identified 191 vOTUs carrying 40 auxiliary metabolic genes (AMGs) mapped to 31 metabolic pathways. These AMGs were mainly associated with sulfur metabolism, cysteine and methionine metabolism, folate biosynthesis, and one-carbon pool by folate pathways. Comparative analysis under this study design showed that domestic pigs harbored higher viral diversity with a greater number of unique vOTUs (n = 12,611) than wild boars (n = 3,072). Domestic pigs viromes were enriched in Circoviridae and Microviridae, whereas wild boars showed higher relative abundances of Adintoviridae and Genomoviridae. Putative AMGs related to coenzyme synthesis and DNA methylation were more frequently detected in domestic pigs, whereas AMGs associated with nucleotide biosynthesis and cofactor metabolism were enriched in wild boars. These findings characterize the composition and functional potential of lung-associated DNA viral communities in pigs and provide a resource for future respiratory virome studies.