Image Courtesy: MIT News

MIT engineers have developed bacteria that can function like transistors, opening the door to living circuit boards that can be printed onto growth material and perform basic computing inside biological systems.

The researchers engineered individual bacterial cells to act as transistor-like switches, controlling chemical signals that carry information between different parts of a circuit. The approach could eventually allow biological circuits to be placed on plants, where they could monitor environmental conditions and trigger responses to threats such as drought or pests.

The study, published in Nature Chemical Biology, describes two types of bacterial transistors along with three bacterial strains that function as biological relays. Together, the five strains can be combined into different circuit configurations.

The researchers used Pantoea agglomerans, a bacterium commonly found on plant surfaces. Both transistor strains respond to the molecule OC-6, with one switching on and the other switching off. They can also detect OC-12 and, depending on the transistor’s state, produce another signaling molecule called OHC-14.

The three relay strains receive that signal and convert it into another output that can be passed to a neighboring bacterial colony. By positioning colonies on agar plates roughly 5 millimeters apart, the researchers effectively created biological wiring. The spacing limits the distance chemical signals can travel, helping information move through the circuit in a controlled direction.

The system can perform several logic operations, including multi-input, OR, and implication gates. Researchers also demonstrated circuits capable of adding two signals, processing multiple inputs, and operating as a demultiplexer, which directs a single incoming signal to a selected output.

The largest circuit in the study contained 24 connected bacterial colonies and was designed to add two inputs together. Lead author Hamid Doosthosseini said the five bacterial strains could be used to construct a wide range of computational operations.

Unlike conventional electronics, however, these biological computers are extremely slow. A calculation takes roughly eight hours to complete. MIT researchers say that limitation may not matter for applications where biological processes themselves unfold over hours or days.

The team’s longer-term goal is to create circuits that can operate directly on plants. A system placed on a leaf or root could potentially recognize environmental signals and activate a biological response, such as producing a substance that protects the plant from disease.

Senior author Christopher Voigt emphasized that the goal is not to replace electronic computers, but to bring computation into living systems. If successful, the technology could turn plants and other organisms into biological platforms capable of sensing their surroundings and making simple decisions.