Wednesday, December 16, 2009

The most marvelous world of the virus

A superb essay on the virus ...
A Gazillion Tiny Avatars - Olivia Judson -

.... whether you count viruses as living or not, there’s an awfully large number of them: a single drop of seawater may contain more than 10 million viral particles. That’s more than 10 billion in a liter (two-and-a-bit pints) of ocean. Some people have estimated that, in the oceans, there’s more carbon stashed away in viruses than there would be in 75 million blue whales.

Moreover, viruses are extremely diverse; there are zillions of different kinds. Some, such as MS2, a virus that attacks bacteria like Escherichia coli, have as few as four genes. Others, such as the gargantuan Mimivirus, have more than 900. (Mimivirus mostly attacks amoebae, although it is also suspected of occasionally causing pneumonia in humans.) And each time we look in a new place, we find more and more viruses that are different from those we have known before.

Fortunately for us, most viruses don’t attack humans; they attack bacteria and other microbes, which they kill on a colossal scale. In the oceans alone, viruses are reckoned to kill about 100 million metric-tons’-worth of microbes every minute.
.... viruses play a fundamental role in regulating the food chain. This is because death-by-virus is different from death-by-predator. When a predator kills a microbe, it consumes it: the microbe’s cell is incorporated into the predator’s body. In contrast, when a virus kills a microbe, the microbe’s cell bursts open, or “lyses,” releasing new viruses and a lot of cellular debris back into the environment. This debris can then be consumed by other microbes. In other words, by lysing their victims, viruses are constantly making food available to other life forms...
So do bacteria have a fundamentally different relationship to viruses than multicellular organisms? Why are they so much more lethal to bacteria than to us? Did the way our DNA propagates facilitate a "truce" with viruses?
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