Some scientists envision that biological engineers will one day sit at computers writing programs for cells, like software developers. But the code would be written in sequences of DNA, rather than computer language. When finished, the programmer would press the "print" button, as it were, and the DNA would be made to order.
The field is also starting to attract some investment. In June, venture capitalists put US$13 million into Codon Devices, a startup company in Cambridge, Massachusetts, that is developing a way to synthesize long stretches of DNA far less expensively than existing methods. The founders include Church, Endy and Keasling.
Keasling is also a co-founder of Amyris Biotechnologies, which is helping make the malaria drug. And Venter has started Synthetic Genomics to work on his energy-producing microbes.
What makes the engineering approach possible are the inner workings of a living cell. Genes, made of DNA, contain the instructions for producing proteins, which carry out most functions in cells. Some proteins can bind to DNA, turning partic-ular genes on or off. This interplay, which is one way that cells regulate themselves, is not too different from how electronic circuits function, with one transistor turning another on or off.
Some newer efforts involve trying to manipulate entire colonies of microbes to cooperate with one another. They take
advantage of something called quorum sensing, a natural communications system that bacteria use to determine whether there are enough of them present to mount an attack.
The demonstrations, however clever, also illustrate problems inherent in designing biological circuits, as opposed to silicon ones. One is that living things are always dividing and evolving.
Indeed, the population-control system breaks down within days because some of the bacteria mutate so that the suicide gene is not switched on.
Those bacteria, having a selective advantage, quickly take over the colony, said Lingchong You, lead researcher on the
project at Caltech and now an assistant professor of biomedical engineering at Duke.
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