May 2000

Biological Computing

A vial of bacteria capable of computation? Injectable cells that survey the bloodstream and produce drugs on demand? These ideas might not be as far-fetched as they sound.

By Simson L. Garfinkel

Today's silicon-based microprocessors are manufactured under the strictest of conditions. Massive filters clean the air of dust and moisture, workers don spacesuit-like gear and the resulting systems are micro-tested for the smallest imperfection. But at a handful of labs across the country, researchers are building what they hope will be some of tomorrow's computers in environments that are far from sterile-beakers, test tubes and petri dishes full of bacteria. Simply put, these scientists seek to create cells that can compute, endowed with "intelligent" genes that can add numbers, store the results in some kind of memory bank, keep time and perhaps one day even execute simple programs.

All of these operations sound like what today's computers do. Yet these biological systems could open up a whole different realm of computing. "It is a mistake to envision the kind of computation that we are envisioning for living cells as being a replacement for the kinds of computers that we have now," says Tom Knight, a researcher at the MIT Artificial Intelligence Laboratory and one of the leaders in the biocomputing movement. Knight says these new computers "will be a way of bridging the gap to the chemical world. Think of it more as a process-control computer. The computer that is running a chemical factory. The computer that makes your beer for you."

As a bridge to the chemical world, biocomputing is a natural. First of all, it's extremely cost-effective. Once you've programmed a single cell, you can grow billions more for the cost of simple nutrient solutions and a lab technician's time. In the second place, biocomputers might ultimately be far more reliable than computers built from wires and silicon, for the same reason that our brains can survive the death of millions of cells and still function, whereas your Pentium-powered PC will seize up if you cut one wire. But the clincher is that every cell has a miniature chemical factory at its command: Once the organism was programmed, virtually any biological chemical could be synthesized at will. That's why Knight envisions biocomputers running all kinds of biochemical systems and acting to link information technology and biotechnology.

All of these operations sound like what today's computers do. Yet these biological systems could open up a whole different realm of computing. "It is a mistake to envision the kind of computation that we are envisioning for living cells as being a replacement for the kinds of computers that we have now," says Tom Knight, a researcher at the MIT Artificial Intelligence Laboratory and one of the leaders in the biocomputing movement. Knight says these new computers "will be a way of bridging the gap to the chemical world. Think of it more as a process-control computer. The computer that is running a chemical factory. The computer that makes your beer for you."

As a bridge to the chemical world, biocomputing is a natural. First of all, it's extremely cost-effective. Once you've programmed a single cell, you can grow billions more for the cost of simple nutrient solutions and a lab technician's time. In the second place, biocomputers might ultimately be far more reliable than computers built from wires and silicon, for the same reason that our brains can survive the death of millions of cells and still function, whereas your Pentium-powered PC will seize up if you cut one wire. But the clincher is that every cell has a miniature chemical factory at its command: Once the organism was programmed, virtually any biological chemical could be synthesized at will. That's why Knight envisions biocomputers running all kinds of biochemical systems and acting to link information technology and biotechnology.

Realizing this vision, though, is going to take a while. Today a typical desktop computer can store 50 billion bits of information. As a point of comparison, Tim Gardner, a graduate student at Boston University, recently made a genetic system that can store a single bit of information-either a 1 or a 0. On an innovation timeline, today's microbial programmers are roughly where the pioneers of computer science were in the 1920s, when they built the first digital computers.

Indeed, it's tempting to dismiss this research as an academic curiosity, something like building a computer out of Tinker Toys. But if the project is successful the results could be staggering. Instead of painstakingly isolating proteins, mapping genes and trying to decode the secrets of nature, bioengineers could simply program cells to do whatever was desired-say, injecting insulin as needed into a diabetic's bloodstream-much the way that a programmer can manipulate the functions of a PC. Biological machines could usher in a whole new world of chemical control.

In the long run, Knight and others say, biocomputing could create active Band-Aids capable of analyzing an injury and healing the damage. The technology could be used to program bacterial spores that would remain dormant in the soil until a chemical spill occurred, at which point the bacteria would wake up, multiply, eat the chemicals and return to dormancy.

In the near term-perhaps within five years-"a soldier might be carrying a biochip device that could detect when some toxin or agent is released," says Boston University professor of biomedical engineering James Collins, another key player in the biocomputing field.