Viruses are the most abundant biological entities in soil, which reached to 1010 virus particles per gram soil. Viruses could affect the community composition of other microorganisms, mediate biogeochemical cycles, regulate microbial evolution, and even threaten plants, animals and human health. However, there is very limited knowledge of the distribution patterns of viruses in complex agricultural soil ecosystems.
In the present study, diverse ssDNA viruses and some dsDNA viruses were identified from six soils collected from Chinese typical agricultural ecosystems. Twenty-eight families were identified by MG-RAST, in which ssDNA viruses were the most abundant in all soils. The majority of viral sequences belonged to Microviridae, with Chlamydiamicrovirus being the most abundant genus, followed Microvirus and Bdellomicrovirus. Other ssDNA viruses identified at low abundance including Inoviridae, Geminiviridae, Nanoviridae and Circoviridae. Only 8.83% of the sequences showing similarity to dsDNA viruses Caudovirales were observed. Furthermore, 16.17% of the sequences shared identity with unclassified of viral family. A wide range of molecular functions were also found in our six viromes, some were required for reproduction of viruses themselves, while others were likely related to metabolic functions. The majority of functional genes belong to phages, prophages, transposable elements and plasmids, and also including amino acid, nucleatide and carbohydrate, nitrogen, sulfur and phosphorus metabolism.
Our study represents a broad survey of virus diversity in six typical Chinese agricultural soils and has demonstrated that the taxonomic and functional genes of viruses are diverse and largely uncharacterized. The taxonomic and functional diversity of viruses observed in the soils will aid future soil metaviromic study and enhance our understanding of ecological functions of soil viruses.