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Planet Earth

Deadly, Tiny, and Ready For Its Close-up, Mr. DeMille

The LoomBy Carl ZimmerAugust 27, 2004 1:11 AM


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If you took a census of life on Earth, you'd probably find that the majority of life forms looked like this. It's a virus known as a bacteriophage, which lives exclusively in bacteria. There are about 10 million phages in every milliliter of coastal sea water. All told, scientists put the total number of bacteriophages at a million trillion trillion (10 to the 30th power). Bacteriophages not only make up the majority of life forms, but they are believed to have existed just about since life itself began. Since then, they have been evolving along with their hosts, and even making much of their hosts' evolution possible by shuttling genes from one host to another. Thanks in large part to bacteriophages, more and more bacteria are acquiring the genes they need to defeat antibiotics. Bacteriophages also kill off a huge portion of ocean bacteria that consume greenhouse gases. If you suddenly rid the world of all bacteriophages, the global climate would lurch out of whack. It may seem strange that the world's most successful life form looks a bit like the ship-drilling robots that swarmed through The Matrix. But the fact is that the bacteriophage is nanotechnology of the most elegant, most deadly sort. To get a real appreciation of its mechanical cool, check out the movie from which this picture comes. (Big and small Quicktime.) The movie is based on the awesome work of Michael Rossmann of Purdue University and his colleagues. (Their most recent paper appears in the latest issue of Cell, along with even more cool movies.) Rossmann and company have teased apart pieces of a bacteriophage and have gotten a better understanding of how they work together. The phage extends six delicate legs in order to make contact with its host, E. coli.. Each leg docks on one of the bacteria's receptors, giving the phage the signal that it is time to inject its DNA. The legs bend so that its body pulls towards the bacterium. The pulling motion makes the base of the phage begin to spin like the barrel of a lock. A set of shorter legs, previously held flush against the base of the virus, unfold so that they can clamp onto the microbe's membrane. The phage's sheath, shown here in green, shrinks as its spiralling proteins slide over one another. A hidden tube emerges, which in turn pushes out a needle, which rams into the side of the bacterium. The needle injects molecules that can eat away at the tough inner wall of the microbe, and the tube then pushes all the way into the microbe's interior, where it unloads the virus's DNA. It has taken a while, historically speaking, for scientists to come to appreciate just how sophisticated parasites such as bacteriophages can be, a subject I explored at length in my book Parasite Rex. The best human-designed nanotech pales in comparison to bacteriophages, a fact that hasn't been lost on scientists. Some have been using bacteriophages to build nanowires and other circuitry. Others see them as the best hope for gene therapy, if they can be engineered to infect humans rather than bacteria. In both cases, evolution must play a central role. By allowing the phages to mutate and then selecting the viruses that do the best job at whatever task the scientists choose, the scientists will be able to let evolution design nanotechnology for them. From the depths of deep time, one of the next great advances in technology may come. And perhaps some more work in Hollywood, I hope.

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