Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [99]
I am writing this book only seven years after the birth of synthetic biology, and scientists are still a long way from building E. coli with the equivalent of a computer chip inside. But they have come a long way from toggle switches and blinkers. The E. coli camera is a good example of what they can do now. Each year Massachusetts Institute of Technology hosts a synthetic-biology tournament, in which students try to transform E. coli into various devices. In 2004, students at the University of Texas and the University of California, San Francisco, worked together to make bacteria that could capture an image. They envisioned a film of engineered E. coli that would behave like a piece of traditional photographic film. The bacteria would turn dark unless they were struck by light. The more light that struck them, the less dark they would become. Normally, E. coli cannot sense light, nor can it produce colors. But the students were able to engineer a strain that does both. They borrowed a gene for a light-sensitive receptor from a species of blue-green alga called Synechocystis. To color the microbes, they borrowed genes from Synechocystis that create pigments.
The hard part of the work came when it was time to join the two sets of genes. The students engineered the light receptors so that they could pass a signal to molecules normally made by E. coli. Those molecules were then able to grab on to the microbe’s DNA and shut down the production of Synechocystis’s pigment enzymes. It takes E. coli ten to fifteen hours of exposure to develop an image, which has a rather ghostly appearance. But because each microbe can adjust its own color, the photograph has a very high resolution, about ten times that of a high-resolution printer.
These sorts of experiments give synthetic biologists great hope. Soon it will be possible for them to synthesize entirely new genes from scratch at very little cost. No one can actually invent a completely new gene for a particular function, but it is possible to tinker with existing genes and simulate how their proteins would change as a result. Already researchers have fashioned new genes that allow E. coli to detect nerve gas and TNT. One of the most ambitious projects in all of synthetic biology is taking place at the University of California, Berkeley, where scientists have been developing new genetic circuits that may allow E. coli or yeast to produce a drug for malaria. The drug, known as artemisinin, is normally produced only by the sweet wormwood plant. If a microbe could make artemisinin, the price might drop by 90 percent.
Meanwhile, Christopher Voigt and his colleagues have created strains of E. coli that might someday fight cancer. The microbes seek out tumors by sensing their low levels of oxygen; having found a tumor, they deploy needles to inject toxins into the cancer cells. Voigt hopes someday to turn E. coli or some other microbe into a smart drug, able to make its own decisions about when to produce molecules to treat a disorder. Other researchers are trying to turn E. coli into a solar battery, able to trap sunlight and turn it into fuel. Synthetic biologists plan to move beyond E. coli, just as genetic engineers did. Someday they may be able to hack the programming of human cells, causing them to build new organs.
These are the things synthetic biologists think about when they’re in a good mood. When they’re in a bad mood, they think about all the challenges they still face.
Engineers, for example, need standardized parts. When engineers design a lathe or a lawn mower, they don’t have to design the nuts and bolts that hold the parts together. They just specify which size the nuts and bolts should be. Yet this shortcut is a relatively recent luxury.