MIT Engineers Turn Bacteria Into Living Transistors to Build Biological Circuits

MIT researchers have engineered bacteria to work like transistors, creating living "circuit boards" that can be printed onto growth medium in a Petri dish. In the new system, engineered bacterial cells regulate the movement of small signaling molecules the way a transistor controls electrical current, and those molecules carry information to other components in the circuit. The work, led by MIT postdoc Hamid Doosthosseini and senior author Christopher Voigt, head of MIT's Department of Biological Engineering, was published in the journal Nature Chemical Biology.

The team created two types of bacterial transistors and three additional relay strains, five strains in total that can be arranged to build nearly any kind of circuit, using a bacterium called Pantoea agglomerans that commonly grows on surfaces, including plants. The transistors respond to a molecule called OC 6, with one type switching on and the other switching off when it appears. Depending on whether a second molecule, OC 12, is also present, each transistor produces an output molecule called OHC 14 that the relay strains convert into a signal for the next component in the circuit.

To build a circuit, the researchers printed bacterial colonies about 5 millimeters apart onto agar growth plates, spacing that keeps chemical signals moving in a single direction through the sequence. Using this method, they built circuits that could add two or three inputs together, process multiple signals at once, or act as a demultiplexer that routes one incoming signal to one of several destinations. The largest circuit demonstrated contained 24 interconnected bacterial colonies.

"We've built some initial computer architecture components that are commonly used, but any operation can be built with these five strains," Doosthosseini said. "Computationally, there's nothing that your iPhone can do that these circuits couldn't do," Voigt said, though each calculation takes about eight hours, far longer than an electronic computer would need.

One potential application is agriculture: the researchers say the living circuits could eventually be placed on plant roots to detect stress such as drought or pest attack and trigger a response, such as producing a fungicide.