Scientists at MIT have engineered bacteria to work like tiny transistors, creating “living circuits” that can process information and perform basic calculations.
The technology could eventually allow plants to detect problems such as drought or pests and automatically respond.
In ordinary electronics, transistors are tiny switches that control the flow of electrical current. Billions of them work together inside computers and smartphones to perform calculations.
The MIT team has now created a biological version in which engineered bacterial cells act as switches and communicate using chemical signals instead of electricity.
The researchers developed two types of bacterial transistors and three additional bacterial strains that act as relays, passing information from one transistor to another.
Together, these five strains provide basic building blocks that can be arranged into many different biological circuits.
The study, published in Nature Chemical Biology, takes a different approach from previous attempts to create biological computers.
Traditionally, scientists have tried to put an entire biological circuit inside a single cell by engineering it to produce different proteins. But the number of biological components available for this purpose is limited, and putting too many functions inside one cell can overwhelm its machinery.
Instead, the MIT researchers divided the work among many cells. Each bacterial colony performs a relatively simple job, much like individual electronic components connected together on a circuit board.
The team used a bacterium called Pantoea agglomerans, which naturally grows on many surfaces, including plants. They engineered different versions of the bacterium to detect specific molecules, switch their activity on or off and produce chemical signals that neighboring colonies can receive.
To build circuits, the researchers printed colonies of bacteria onto plates containing agar, a jelly-like material that provides nutrients for bacterial growth. The colonies were placed about 5 millimeters apart. This spacing allows chemical signals to reach nearby colonies without spreading too far, helping information travel through the circuit in a controlled direction.
The researchers showed that their living circuits could perform several logic operations similar to those used in conventional computers. They also created more complicated systems capable of combining two or three inputs and directing an incoming signal toward different destinations. Their largest circuit contained 24 bacterial colonies working together.
These biological computers are certainly not fast. A calculation takes around eight hours. By comparison, electronic computers perform billions of operations every second.
But speed is not the goal.
The researchers want to bring computing abilities directly into living systems rather than replace conventional computers. In agriculture, for example, engineered bacteria could potentially live around plant roots and continuously monitor environmental conditions. A biological circuit might detect a combination of signals indicating drought, disease or pest attack and then trigger an appropriate response.
If a plant showed signs of fungal infection, for instance, the bacteria might respond by producing a substance that fights the fungus.
The technology remains at an early stage, but the researchers believe increasingly sophisticated biological circuits could be constructed by connecting simple bacterial components.
Instead of putting a computer next to a living organism, future technology may allow the living system itself—and the microbes surrounding it—to do some of the computing.
