... between viruses and bacteria. From NBC News:
The discovery of new viruses that appear to be spread around the world's oceans hints at a war waging between such viruses and their prey: an abundant group of bacteria.
The bacteria, collectively known as SAR11, are the most abundant organisms known to inhabit seawater.
They are everywhere, from the surface down to the bottom, from pole to pole," said study researcher Stephen Giovannoni, a professor of microbiology at Oregon State University, adding that SAR11 microbes are most abundant in the warm waters of ocean gyres, or rotating currents, where they can account for as much as 40 percent of plankton cells.
... In 1990, Giovannoni's lab first identified these microbes using DNA (the genetic code deoxyribonucleic acid) found in water collected near Bermuda in the Sargasso Sea. Microbes in this group were later identified in waters around the world.
More recently, using samples collected from the Sargasso Sea as well as from coastal Oregon waters, Giovannoni's team identified the four new viruses, which, the team found, killed SAR11 cells in laboratory experiments. They dubbed the viruses "pelagiphages," because they infect bacteria in the open ocean.
The team sequenced the genomes of these pelagiphages and compared these with DNA from other viruses. They found similarities between the pelagiphages and viruses that attack other ocean-dwelling bacteria. One of the new viruses, however, was so new that it created a new group, called a subfamily, of so-called podoviruses.