Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [37]
The followers of Darwin and Lamarck clashed for decades. Uncertainty kept the fights going, because scientists could not get a close look at the chemistry behind heredity. They needed an organism they could observe reproducing and acquiring an adaptation generation by generation. What they needed, it turned out, was E. coli.
SLOT MACHINES AND VELVET STAMPS
One night in 1942 in Bloomington, Indiana, an Italian refugee sat in a country club, teasing a friend at a slot machine.
The refugee was named Salvador Luria. He had trained as a doctor in Turin, but when he discovered viruses and bacteria he abandoned his medical career for research. During World War II he fled Italy for Paris, where he joined the scientists at the Pasteur Institute studying E. coli and its viruses. As the Germans closed in on Paris, Luria fled again, this time to New York. In the United States he met his hero, Max Delbrück, and the two began to work together. The scientists explored the life cycles of viruses as the viruses slipped in and out of E. coli. They collaborated with scientists working with the newly invented electron microscope to spy on the creatures as they invaded their hosts. And for several years, Luria and Delbrück puzzled over how E. coli recovers from the plagues visited on it by scientists.
In a typical experiment, researchers would add viruses to a dish full of bacteria, and the bacteria would completely disappear from view. But the viruses did not kill them all. After a few hours the survivors would produce visible colonies once more. The bacteria in the new colonies were all resistant; if the scientists moved them into fresh petri dishes and exposed them to the same viruses, their offspring would resist infection, too.
This sort of behavior in bacteria turned a lot of microbiologists into neo-Lamarckians. E. coli seemed to respond to viruses the same way shorebirds responded to mud. The challenge had caused them to acquire resistance, which they could then pass on to their descendants. Other experiments seemed to fit this pattern as well. When scientists switched E. coli’s diet from glucose to lactose, it began to produce the enzyme necessary for feeding on lactose, as did its descendants. And one other factor also made many microbiologists into neo-Lamarckians: there was little evidence that bacteria had genes. As far as many microbiologists could tell, a microbe such as E. coli was nothing but a bag of enzymes and other molecules that could react to changes in its environment.
But some microbiologists thought otherwise. They argued that bacteria did have genes, and that, like the genes of animals, these could mutate spontaneously. In some cases, a mutation might, through pure luck, give a microbe an advantage, such as resistance to a virus. According to this rival explanation, E. coli followed Darwin’s rules, not Lamarck’s.
No one had put the alternatives to a good test, and Luria and Delbrück spent months puzzling over how they might do so. They had failed to come up with an experiment by 1942, when they parted ways after Luria accepted a job at Indiana University, “a place I had never heard of,” he wrote later. Not long afterward Luria found himself in Bloomington sitting next to a colleague who was playing a slot machine. The professor was losing, and when Luria teased him he stalked off.
“Right then I began giving some thought to the actual numerology of slot machines,” Luria wrote in his autobiography.
The slot machine the professor was playing was programmed to deliver only a few big jackpots. It might have been built differently. It might have provided the same small chance of paying out a jackpot on every pull of the arm. In that case the jackpot would have given out many more prizes, but much smaller ones. Suddenly Luria realized he had figured out how to run an experiment on E. coli’s resistance that could test Darwin’s theory versus Lamarck’s.
The next day Luria