A Planet of Viruses - Carl Zimmer [15]
While Collins and other scientists discover how to make phages even more effective, antibiotics are now losing their luster. Doctors are grappling with a growing number of bacteria that have evolved resistance to most of the antibiotics available today. Sometimes doctors have to rely on expensive, last-resort drugs that come with harsh side effects. And there’s every reason to expect that bacteria will evolve to resist last-resort antibiotics as well. Scientists are scrambling to develop new antibiotics, but it can take over a decade to get a new drug from the lab to the marketplace. It may be hard to imagine a world before antibiotics, but now we must imagine a world where antibiotics are not the only weapon we use against bacteria. And now, ninety years after Herelle first encountered bacteriophages, these viruses may finally be ready to become a part of modern medicine.
The Infected Ocean
Marine Phages
Some great discoveries seem at first like terrible mistakes.
In 1986 a graduate student at the State University of New York at Stony Brook named Lita Proctor decided to see how many viruses there are in seawater. At the time, the general consensus was that there were hardly any. The few researchers who had bothered to look for viruses in the ocean had generally found only a scarce supply. Most experts believed that the majority of the viruses they did find in sea water had actually come from sewage and other sources on land.
But over the years, a handful of scientists had gathered evidence that didn’t fit neatly into the consensus. A marine biologist named John Sieburth had published a photograph of a marine bacterium erupting with new viruses, for example. Proctor decided it was time to launch a systematic search. She traveled to the Caribbean and to the Sargasso Sea, scooping up seawater along the way. Back on Long Island, she carefully extracted the biological material from the seawater, which she coated with metal so that it would show up under the beam of an electron microscope. When Procter finally looked at her samples, she beheld a world of viruses. Some floated freely, while others were lurking inside infected bacterial hosts. Based on the number of viruses she found in her samples, Proctor estimated that every liter of seawater contained up to one hundred billion viruses.
Proctor’s figure was far beyond anything that had come before. It would have surprised few scientists if she had turned out to have added on a few extra zeroes by accident. But when other scientists carried out their own surveys, they ended up with similar estimates. Scientists came to agree that there are somewhere in the neighborhood of 1,000,000,000,000,000,000,000,000,000,000 viruses in the ocean.
It is hard to find a point of comparison to make sense of such a huge number. Viruses outnumber all other residents of the ocean by about fifteen to one. If you put all the viruses of the oceans on a scale, they would equal the weight of seventy-five million blue whales. And if you lined up all the viruses in the ocean end to end, they would stretch out past the nearest sixty galaxies.
These numbers don’t mean that a swim in the ocean is a death sentence. Only a minute fraction of the viruses in the ocean can infect humans. Some marine viruses infect fishes and other marine animals, but by far their most common targets are microbes. Microbes may be invisible to the naked