MIT researchers have engineered bacteria to function as transistors, creating living circuit boards that can be printed onto a growth medium in a Petri dish.
In electrical circuits, transistors act as switches that turn current on or off. The biological transistors the MIT team developed control the flow of small molecules that send signals to downstream circuit components. The researchers designed two different transistors, along with three bacterial strains that relay information between them, giving them the building blocks needed to construct nearly any type of circuit.
Bacterial Transistor Design
“We’ve built some initial computer architecture components that are commonly used, but any operation can be built with these five strains,” said Hamid Doosthosseini, an MIT postdoc and the lead author of the study.
The team used a bacterium called Pantoea agglomerans, which commonly grows on plant surfaces. They created two types of transistors that can be switched on or off by a molecule called OC-6. One transistor switches on with this input; the other switches off. Each transistor also detects a target molecule called OC-12 and, depending on whether that molecule is present and whether the switch is active, produces an output molecule known as OHC-14.
The three relay strains translate the OHC-14 signal into an output that can feed into another transistor, allowing the team to wire the transistors together like an electronic circuit board. The researchers printed bacterial colonies onto agar plates, with each colony placed about 5 millimeters from the nearest one. This spacing ensures signals travel only to adjacent colonies, allowing information to flow in one direction.
Circuit Capabilities
In their study, the researchers demonstrated a transistor that can perform multiple logic operations depending on its circuit location, including multi-input, OR, and IMPLY gates. They also combined transistors to create more complex circuits capable of adding two signals, processing multiple signals simultaneously, or functioning as a demultiplexer that routes a single incoming signal to one of several possible destinations based on a control signal. The most complex circuit, which adds two inputs together, links 24 bacterial colonies.
“This work shows that we can get toward more complicated functions by linking up simpler functions in individual cells,” said Christopher Voigt, head of MIT’s Department of Biological Engineering and senior author of the paper. “Computationally, there’s nothing that your iPhone can do that these circuits couldn’t do.”
These biological circuits take approximately eight hours to complete each calculation, far slower than electronic computers. For biological applications, however, that timeframe is practical.
Potential Applications
“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,” Voigt said.
Potential applications include coating plant roots or leaves with circuits that detect and respond to environmental conditions such as drought or pest attacks, triggering responses like synthesizing fungicides. The research appears in Nature Chemical Biology, with funding from the U.S. Defense Advanced Research Projects Agency and the U.S. Intelligence Advanced Research Projects…