Proportion of BLAST hits to sequences from various sources. Donut charts illustrating the proportion of sequences in the Monterey Bay viral metagenome library that had significant (E-value ≤ 10-3), best blastx matches to bacteriophages, eukaryotic viruses, mobile genetic elements, or members of the Domains Bacteria, Archaea, or Eukarya, or which had no significant match (E-value > 10-3). Panel A: BLAST results when using only the GenBank nr database. Panel B: the distribution of top-scoring matches when sequence data from viral and microbial metagenomes were included in the analysis. In Panel B, eukaryotic viruses, bacteriophages, and mobile genetic elements were combined into the single category "Viruses" and bacteria and archaea were combined into the category "Prokaryotes".