Figure 2.

Overview flow-chart of the VIROM classification scheme for environmental peptides. BLAST homology data from the sequence analysis pipeline (Figure 1) serves as input to the classification decision tree. Peptides having a significant hit (E ≤ 0.001) to a sequence in UNIREF 100 are placed in the ‘Known protein’ bin. If one of the homologs has a meaningful annotation, the viral metagenome predicted peptide is considered a ‘Functional protein’. If not, the peptide is considered an ‘Unassigned protein’. Peptides having only a significant hit to an environment peptide in the MGOL database are placed in the ‘Environment protein’ bin. Within this bin, peptides that hit only environmental proteins within either microbial or viral metagenome libraries are classified as ‘Only microbial hit’ or ‘Only viral hit’, respectively. Peptides having hits to protein within viral and microbial metagenome libraries are classified as either ‘Top-hit microbial’ or ‘Top-hit viral’ depending on whether the top BLAST hit came from a microbial or viral metagenome library, respectively. A predicted viral metagenome peptide having no significant hit to a protein within the UniRef 100 or MGOL sequence databases is classified as an ‘ORFan’.