At any moment, a microscopic arms race could be under way inside you. Humans are in a constant battle against invisible “bugs” that make us sick. But some bugs, like the bacteria that give us food poisoning, are often under attack by even smaller bugs—viruses called bacteriophages (phages, for short). A phage’s only mission in life is to make more phages. It needs bacteria—more specifically, bacteria’s protein-assembly machinery—to reproduce. Phages use special protein keys to “pick” locked ports in cell walls and inject their own genetic material (DNA or RNA) into carefully chosen host cells. Phage genes then hijack the bacteria and force them to build armies of new phages inside themselves. One type of phage forces the bacterium to make more and more new phages until it explodes, sending thousands of them out on the prowl for more victims. Others are sneakier—they slip phage genes into the bacterial DNA, and as the bacterium multiplies, so do the secret plans to build new phages. Over time, many generations harbor these phage plans until something turns the phage genes on. Then the bacteria start to manufacture the thousands of new phages that will eventually kill off their own cells. But don’t feel too sorry for bacteria—they can actually defend themselves from phage attacks. One lucky mutation can change the lock so that the phage can no longer pick it. Eventually, though, a fortunate phage’s “key” mutation will fit the lock, and then the arms race rages on.

As evil as they sound, phages could be allies in our battle against human disease. Because they are specific in their targets, scientists think that we could treat bacterial illness with a mixture of different types of phages. Maybe such treatments would work better than drugs (antibiotics) often prescribed today.

Thanks to phage hunters and Pitt profs Roger Hendrix and James Conway, who filled us in on the wily ways of these microbes. The “corn dog” phage shown above was originally isolated by Pitt’s Bill Brucker.

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Image courtesy of University of Pittsburgh's Graham Hatfull, Deborah Jacobs-Sera, and Welkin Pope of Arts and Sciences and Pitt's James Conway, Alexander Makhov, and Alexis Huet of the School of Medicine.