MIT engineers assembled living transistors from bacteria that perform one calculation every 8 hours

Modern electronics rely on simple patterns for passing along and processing signals. Living organisms have worked this way for billions of years, and that similarity hasn't gone unnoticed by engineers.

A team at the Massachusetts Institute of Technology swapped electrical signals for biological ones. Their prototype relies on three strains of the bacteria Pantoea agglomerans, which carry signals through a circuit in place of electrons.

Each calculation takes around eight hours, but the results, published this week in Nature Chemical Biology, point to an unexpected potential for biotechnology. This isn't about competing with silicon – it's about building logic directly into living systems.

Christopher Voigt, head of MIT's Department of Biological Engineering and the study's senior author, said:

We're not trying to replace computers, but rather put computational control into biology. If you have bacteria on the root of a plant, or the plant itself is doing the computing, running a simple calculation overnight is fast enough relative to a growth season.

Earlier attempts in this space relied on enzymes and packed an entire circuit into a single, relatively large cell. Getting a tiny cell to compute exactly the way researchers wanted turned out to be extremely difficult, which put a hard cap on how complex these systems could get.

Transistors work differently. As the researchers wrote, they "do not define circuit logic" but "conditionally enable signal propagation." That approach lets bio-transistors combine in different arrangements to build more varied circuits.

For the prototype, the team printed bacterial colonies onto tiny plates, spacing them about five millimeters apart. The mechanism relies on a family of molecules long used in biochemical research.

One molecule acts as a switch, while a second serves as a "target" that indicates whether the switch is active. When the target molecule is present, the transistor produces an output molecule that gets passed along to the next element in the chain.

Testing showed the setup could handle a fair number of logical operations using just five strains. The largest circuit assembled linked together 24 bacterial colonies.

The technology still faces plenty of limitations. Among the main factors holding back scaling:

• the colonies are living organisms that grow and change over time

• speed is capped by the natural diffusion of molecules between colonies

• the entire "living computer" only functions for around three days

This isn't going to compete with office computers, but agriculture looks like a genuinely promising application. The circuit could sit near plant roots to track stress conditions and respond on its own to pests or other environmental threats.

Christopher Voigt:

This work shows that we can get toward more complicated functions by linking up simpler functions in individual cells. Computationally, there's nothing that your iPhone can do that these circuits couldn't do.

Despite the progress, practical applications are still a ways off.