Analysis Of Deep-sea Sediment Viral Metagenome And Herpesvirus Genome

In the deep-sea ecosystem,there exist abundant viral particles.The viruses can participate in the global biogeochemical cycles by affecting their hosts' life cycles.Characterizations of the metagenomes of viruses in the deep-sea sediments will be helpful to reveal the types,abundances and distribution characteristics of deep-sea viruses,as well as to obtain the information about the potential pathogenic viruses in the deep sea.In this study,50 deep-sea sediment samples from different latitudes,different depths and different deep-sea environments including seamounts,mid-ocean ridges,hydrothermal vents and cold seeps were collected.These samples were subjected to virus isolation and purification,viral genomic DNA extraction and genome amplification.Subsequently the metagenomes of deep-sea viruses were analyzed.The results of transmission electron microscopy revealed that there were many viruses with various morphologies in the deep-sea sediments.High-throughput sequencing of deep-sea sediment viral metagenomes yielded a total of 1,271,381,283 reads(sequences)and 1,293,316 contigs(spliced sequences).These viruses contained 73,678 OTUs(taxonomic units).The comparison analysis of the viral metagenome sequences with the virus database established by our laboratory showed that ~ 77% of the deep-sea viruses were unknown,~23% viruses were known.The known viruses belonged to 25 viral families.In the known deep-sea viruses,Podoviridae was the most abundant viral family,followed by Siphoviridae,Polyomaviridae,Poxviridae,Genomoviridae,Microviridae,Myoviridae,Nimaviridae,Genomovirida and Circoviridae.It was found that the viral types,abundance and distribution of deep-sea sediments changed significantly with the different ecological environments,depths and and latitudes.COG(clusters of orthologous groups of proteins)analysis indicated that the deep-sea viruses were involved in gene transcription,DNA replication,recombination and repair,amino acid transport and metabolism,inorganic ion metabolism and transport,energy production and conversion,carbohydrate transport and metabolism,membrane biogenesis,signal transduction,post-transcriptional modification,and ribosome structure and biogenesis.KEGG(Kyoto encyclopedia of genes and genomes)metabolic pathway analysis revealed that the functional genes of deep-sea viruses could participate in 245 metabolic pathways,mainly including the biosynthesis of host secondary metabolites,antibiotic biosynthesis,amino acid metabolism,two-component system,carbon metabolism,purine metabolism,pyruvate metabolism,pyrimidine metabolism,and carbon fixation pathways of prokaryotes,etc.The results of metagenome analysis of deep-sea sediment viruses showed that there might be pathogenic herpesvirus in the deep-sea sediments.Thus,a herpesvirus-sensitive cell line was used to isolate herpsevirus from deep-sea sediments.As a result,a herpesvirus named D152 was purified.The genome size of D152 was 125,249 bp.It's G + C content was approximately 46.3%.The virus could encode 69 open reading frames(ORFs).The data of sequence analysis revealed that D152 was highly homologous with human herpesvirus type 3.Therefore,our findings demonstrated that there was pathogenic herpesviruse in the deep sea.