The bacteria control chemical signals much as electronic transistors control current. Arranged in patterns, their colonies can perform calculations.
Engineers at MIT have assembled bacterial switches into living circuit boards, printed as colonies on nutrient medium in a Petri dish. Five strains make up the kit: two transistor types and three that pass a signal from one transistor to the next. The paper was published on August 17 in Nature Chemical Biology.
The design gives each cell one transistor instead of packing a whole circuit into it. Synthetic biology usually works the other way, engineering a cell to make proteins whose interactions carry out a task, such as detecting a chemical and triggering an output.
Those circuits need distinct transcription factors to keep signals from interfering, and only so many are available. Too many circuits in one cell also overload its protein-making machinery. Spreading the work across separate cells eases that constraint.
The team used Pantoea agglomerans, a bacterium that commonly grows on surfaces including plants. A control molecule switches one transistor type on and the other off.
Both types also sense a target molecule and produce an output that depends on whether it is present and whether the switch is on. Three relay strains convert that output into a signal another transistor can receive.
The colonies are printed onto agar plates about 5 millimeters apart, so a signal reaches only the nearest neighbor, which passes it on. Information travels one way. Changing the layout lets the same five strains perform different operations without further genetic changes.
The researchers demonstrated several logic gates and combined them into larger circuits. The largest links 24 colonies to add two signals; another routes an input to a chosen destination.
A calculation takes about eight hours. The team told MIT News that an operation completed overnight is quick enough relative to a growing season.
The researchers hope future versions could coat leaves or roots, detect stress and trigger a response such as producing a fungicide.