Amazingly, all the phages on Earth, if placed end to end, would probably extend a distance equivalent to that of the nearest 60 galaxies. In this article in Microbiology Today, Eric Wommack explains how metagenomics is gradually revealing the amazing diversity and abundance of viruses in the biosphere:
Although the throughput and accuracy of methods for viral direct counting has improved since the 1989 report based on transmission electron microscopy, the ‘factor of 10’ ratio of virus to bacterial abundance within aquatic environments has remained a surprisingly common observation. Extrapolating the ‘factor of 10’ rule to the biosphere has lead to estimates that global viral abundance is in the order of 1031 individuals. Assuming an average length dimension of 100 nm, Curtis Suttle has proposed that, lined end-to-end, all the phages on earth would extend a distance equivalent to that of the nearest 60 galaxies (10 million light years, 1024m).