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Spinach, Lettuce, and the Limits of BioterrorismA comforting look back at the major E. coli outbreaks of 2006.

By Carl Zimmer
Posted Wednesday, March 19, 2008, at 12:07 PM ET

(Continued from page 1)

The scientists concluded that at some point in the not-too-distant past, this strain of E. coli O157:H7 evolved rapidly into a far meaner pathogen than its ancestors. Natural selection altered its genes quickly, thanks to the ability bacteria have to reproduce in as little time as 20 minutes. Speeding up their evolution even further was their ability to take in DNA from other microbes, even from species that are only distantly related. The genomes of bacteria are being continually rejiggered into new combinations of genes. Some bacteria become better at capturing sunlight, others at resisting antibiotics. And, in the case of the spinach strain of E. coli O157:H7, the introduction of viral DNA has made them far nastier.

It is chilling to think just how quickly a new, more dangerous form of E. coli has emerged—and it's tempting to think that its quick arrival bodes ill for synthetic biology. After all, if it just takes a few years for a dangerous strain to evolve in the wild, just think how easy it will be for people to build them in the lab.

In fact, the spinach outbreak teaches a very different lesson. The Michigan State scientists have no idea what is making the new strain so mean. It's a straightforward task to identify the hundreds of new genes in its genome, but the researchers can't say precisely what all those new genes are doing. The same goes for the hundreds of missing genes as well as for the other genes tweaked and fine-tuned by natural selection.

This sort of ignorance is par for the course in the world of microbes. And if a new strain of an intensely studied species is so mysterious, it's hard to believe that bioterrorists could just type out a new plague on their keyboards. Our deep ignorance also raises some doubts about how far synthetic biologists can go with the good applications of the science. In the most ambitious projects, scientists have inserted only a few genes. They've had some spectacular successes, such as making E. coli produce jet fuel and precursors to malaria medicine. But the notion that we might add hundreds of genes to bacteria to do something useful, like turn microbes into solar power generators, may be hubris for a long time to come.

Inventors don't always design their inventions from scratch, though. Perhaps someone could create a new pathogen simply by mimicking nature: combining different sets of genes, mutating a few of them, and using trial and error to find ones that worked? Probably not. Nature's lab bench is colossal. Millions of cattle and other animals are carrying around E. coli O157:H7, and an incalculable number of viruses are invading them, trying out new combinations. Many of those combinations turn out to be failures, but natural selection can give rise to a few spectacular successes. Even if a government built a giant lab just for the purpose of stumbling across a new pathogen, it might take centuries or millenniums to hit on something like the spinach strain.

But this ignorance is not cause for much comfort. Even if we don't need to worry about synthetic bacteria just yet, we do need to worry about new pathogens evolving right in our own backyard (or, rather, our own feedlots and factory farms). As things stand, we become vaguely aware of these bacteria only once they've been sickening and killing for years. One way to speed up the search for nature's new bioweapons would be to set up a monitoring network. If public-health workers were equipped with cheap, fast testing devices, E. coli and other microbes might not be able to surprise us so often in the future. And if some evil genius does someday figure out how to unleash a bioweapon, we will have had an excellent rehearsal.

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Science writer Carl Zimmer won the 2007 National Academies Science Communication Award. His next book, Microcosm: E. coli and the New Science of Life, will be published in May.
Photograph of lettuce by John Foxx/Getty Images.
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