Metagenome of healthy blood human donors
10 mL of plasma were filtrated through  1 micrometre filter and subjected to high-speed centrifugation. Subsequent nuclease digestion was performed before independent viral RNA extraction, with the QIAAMP Ultra Sens Virus Kit (Qiagen). RNA was cleaned with TRIzol LS reagent (Invitrogen), extracted with the QIAamp Viral RNA Mini kit and amplified using the QuantiTect Whole Transcriptome kit (Qiagen). RNA amplification products were used for library preparation using Nextera XT DNA library preparation kit (Illumina).