Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [110]
Eleven
N EQUALS 1
I AM STANDING IN MY YARD on a winter night, looking up at a few bright stars asserting themselves against a gibbous moon. I hold up a petri dish of E. coli against the sky. The moonlight shines through the leafless maples into the agar. It gives the colonies a cool, cloudy glow. They look like worlds and stars. I have reached the final question about E. coli, a twist on Monod’s old boast. Is everything that is true for E. coli true for an alien?
One night in October 1957, Joshua Lederberg looked up at the stars as well. He was in Australia, where he was spending a sabbatical. Lederberg was only thirty-two at the time, but he had more than a decade of research behind him, for which he would win a Nobel Prize the following year. He had done most of that work on E. coli. He had discovered that the microbe had sex, and he had used its sex life to draw some of the first maps of its genes. He and his wife had confirmed that genes mutate spontaneously, helping to bring Darwin into the molecular age. They had discovered viruses that could merge into their E. coli hosts. Thanks in large part to Lederberg, E. coli was becoming the standard tool for studying the molecular basis of life, and other scientists were beginning to use it to translate the genetic code.
Now Lederberg was restless. He had come to Australia, to the University of Melbourne, to study the immune system. White blood cells learn to recognize bacteria and other parasites, but they don’t use ordinary genes to encode those lessons. No one at the time knew what language they used. Lederberg would return to the United States recharged, but white blood cells would not be his obsession. Instead, it would be space.
On that night in the Australian spring, Lederberg had gazed up at a moving point of light. It was not a star or even a meteorite but a steel ball hurled into space by humans. Lederberg had a hunch that the Soviet Union’s launch of the first Sputnik satellite was going to change the world.
Lederberg saw in space travel a new frontier for molecular biology. He and other molecular biologists were in the midst of discovering just how uniform life on Earth actually is. E. coli and elephants both encode genes with DNA, both use RNA to carry that information to ribosomes, and both use the same genetic code to translate it into proteins. The uniformity of life was a staggering discovery, Lederberg later wrote, “but its domain has been limited to the thin shell of our own planet, to the way in which one spark of life has illuminated one speck in the cosmos.” Only by going to other worlds would scientists be able to learn whether a similar kind of life had emerged beyond Earth.
Lederberg worried that this awesome opportunity would be ruined if the United States and the Soviet Union ended up in a heedless race into space. In their rush to plant a flag on the moon or Mars, they might contaminate other worlds with microbes from Earth. When Lederberg returned to the United States, he began to lobby the newly formed National Aeronautics and Space Administration to treat outer space like a petri dish, to be kept free of contamination.
He quickly organized meetings at which scientists debated the potential risks of space travel. Unless special precautions were taken, they agreed, a visit to another planet would inevitably leave bacteria there. An astronaut would be “a teeming reservoir of microbial contamination,” as Lederberg wrote. Unmanned probes might pick up millions of bacteria from their human engineers, which they could carry to another world.
A 1959 panel of scientists tried to imagine what would happen if a single E. coli arrived on a planet devoid of life but rich in organic carbon. “The common bacterium Escherichia coli has a mass of 10-12 grams and a minimum fission interval of 30 minutes,” they wrote. “At this rate it would take 66 hours for