Histogram of dN/dS ratios for each metagenome.

A total of 863 genes were included for the cellular metagenome calculation, 191 for the viral metagenome, and 64 for the viral subset. Values are shown only for genes that had a minimum depth coverage of 5 and minimum nucleotide coverage of 100. Frequency values are normalized by percent. Bins are scaled in increments of 0.1 until 1, and then in increments of 0.5. Inset shows mean and 95% confidence intervals for calculated dN/dS for all three data sets, indicating that the average cellular dN/dS is significantly greater than the average dN/dS for the viral metagenome.