VAST NUMBERS. “Viruses are the most abundant ‘life forms’ in aquatic systems, and their number probably exceeds 10(29) in the ocean. Aligning these oceanic viruses and assuming an average diameter of 50 nm for a marine virus, the viral string-of-pearls would be 400,000 light years long. In comparison, the diameter of our galaxy, the Milky Way, is only 25,000 light years.”
http://onlinelibrary.wiley.com/doi/10.1046/j.1462-2920.2003.00539.x/full