A Living Circuit Board Just Ran Calculations Inside a Petri Dish

The circuit board didn't need solder, silicon, or a clean room. It needed a growth medium and bacteria.

A team at MIT built bacteria that behave like transistors, then used them to lay out working circuit boards directly onto a petri dish of growth medium. This is not a metaphor.

A standard transistor is a switch, something that lets current flow or shuts it off. Swap the current for small signaling molecules and the switch for a bacterial colony, and you get the same basic job done by biology instead of silicon: turn a signal on, turn it off, and let it cascade to whatever comes next in the circuit.

Two bacterial strains work as the transistors: one switches on when it detects a signal molecule, the other switches off in response. Three additional strains act as relays, picking up a transistor's output, converting it, and passing it to the next component, the biological equivalent of a wire linking two parts of a circuit board. The largest circuit the team built strung together 24 bacterial colonies to add two numbers.

The bacterium they used, Pantoea agglomerans, commonly grows on surfaces, including plants, which points toward where this is eventually headed. Long-term, the team has its eye on agriculture: living circuits embedded directly in plant tissue, reading environmental stress — drought, pest pressure — and triggering a biological response without human intervention.

The paper was published in Nature Chemical Biology and funded in part by DARPA and the Intelligence Advanced Research Projects Activity. The fact that two intelligence-adjacent agencies are underwriting a living computer is a detail worth sitting with.

The transistor was invented in 1947. It took just under 80 years for someone to rebuild one out of bacteria. Biology was not consulted about this plan, but appears to be cooperating.

Read the full story at MIT News, August 17, 2026

Hot Take: DARPA and IARPA aren't funding bacteria that can add because arithmetic is hard. They're funding computers that might someday grow where silicon can't go.