Differentially abundant metabolic subsystems between microbial and viral metagenomes (mean percentage��s.e., p-values��0.05).

Using this threshold we expect less than one false positive in the data-set. We find that viral metagenomes are significantly enriched for nucleotides and nucleosides and DNA metabolism, consistent with the viruses' need for self-sufficiency. Processes for respiration, photosynthesis, and carbohydrates are overrepresented in microbial metagenomes.