An article in The Scientist discusses the earthshaking changes in the world of virus genomes. Seriously! Giant viruses. Who knew it was gonna be such an exciting Halloween!
The big news is not (just) the size of the virus itself, but the number of base pairs in its genome. (Number of base pairs is how you measure the size of a genome, apparently). Most viruses carry their genetic material in DNA form; a virus with RNA is a retrovirus (retroviruses are less common and tend to have fewer base pairs). While humans have about 3.2 billion base pairs, the first DNA virus to be completely sequenced, Phi X 174, has only about 5,400 bases.
But now researchers reporting in The Proceedings of the National Academy of Sciences have discovered a giant marine virus with 700,000 base pairs. It’s the first giant virus discovered in a marine organism, as The Scientist reports:
Over the past decade or so, scientists have slowly begun identifying viruses that defied the conventional idea that they were tiny infectious agents with highly streamlined genomes.
In 2004, researchers discovered and sequenced the 1.2 million-base pair genome of the largest known virus to date, the mimivirus (although still dwarfed by sequenced multicellular organisms, whose genomes usually exceed 100 million base pairs)…
…The new giant virus, dubbed CroV, is the first to be isolated from a marine organism — a microzooplankton called Cafeteria roenbergensis. They are major consumers of heterotrophic bacteria and phytoplankton, and thus critical to maintaining the delicate balance of marine food webs.
Once thought not to exist in marine environments, scientists now realize that there are some 50 million viruses in every milliliter of seawater. Every day, marine viruses kill about 20 percent of the ocean’s microorganisms, which produce about half the oxygen on the planet.
Microbiologist James Van Etten said of the giant viruses currently devouring the world’s oceans: “There are likely many more; it’s just a matter of people looking.”
…but not behind you.
Whatever you do, don’t look behind you!