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Analog circuits boost power in living computers

New cell-based computers do division and logarithms the old-fashioned way

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Using a molecular dimmer switch that smoothly dials up glowing lights in bacteria, researchers can make calculators in living cells that add, subtract, divide, and even do logarithms.

These analog computations are much more powerful than those of previous, digital-based biological devices, says study author Timothy Lu, a synthetic biologist at MIT.

In biology and electronics, digital computers rely on simple on/off switches to perform calculations. More switches mean more computing power. “Digital is great for electronics because we can put billions of switches together on a single chip,” Lu says. “But it’s not so easy to do that in a cell.”

So Lu and his team designed a DNA-based circuit that can respond to gradual changes in a cell’s environment, rather than all-or-nothing signals.

By making bacteria glow more or less brightly depending on the number of different chemicals around, the new circuit can compute answers to math problems, Lu’s team reports May 15 in Nature. To add 1 plus 1, for example, the circuit would detect two chemicals and crank up the bacteria’s glow to “2.”

The team’s new analog circuit could be useful in biomanufacturing, where, Lu says, engineers could fine-tune cellular production of insulin or other molecules.

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