MIT Researchers Build Biological Circuit Using Bacterial Colonies For Drought, Pest Detection

Researchers at the Massachusetts Institute of Technology (MIT) have created a circuit using live bacteria that can process information and perform calculations. The proposed circuit could eventually be applied to plant leaves or roots to help detect and respond to environmental conditions such as drought and pest attacks. The engineers designed two bacterial strains to act as transistors, which function as biological switches, along with three bacterial strains that relay information between them. Together, these five strains allowed the researchers to build a working biological circuit. 

The researchers’ ultimate vision is particularly interesting: biological circuits could potentially live alongside plants, sense changes in their environment, process those signals and trigger a response.

MIT Builds ‘Living Circuit Boards’ Using Bacteria

The idea may sound like something from science fiction, but the researchers have essentially found a way to make living bacterial cells work like components of a circuit.

In a conventional electronic circuit, a transistor acts as a switch that can turn electrical current on or off. In MIT’s biological circuit, there is no electrical current flowing through the bacteria. Instead, the bacterial switches control the flow of small molecules, which carry signals to other components of the circuit. 

The researchers used a bacterium called Pantoea agglomerans, which commonly grows on surfaces, including plants. They engineered two types of transistors and three additional strains of the same bacterium to act as relays. These components can then be connected in different ways to create different circuits. 

“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 lead author of the study. 

How Do The Bacterial Transistors Work?

The two bacterial transistors are designed to respond to chemical signals. One transistor can be switched on, while the other can be switched off, by a molecule called OC-6. Each transistor also detects another molecule called OC-12.

Depending on whether OC-12 is present and whether the biological switch is active, the transistors produce another molecule called OHC-14. This molecule then acts as a signal that can be passed to another part of the circuit. 

In simple terms, the bacteria can detect a signal, process it and produce another signal.

That is similar to the basic idea behind an electronic circuit, although the mechanism here is biological rather than electrical.

Three Bacterial Strains Relay The Information

The researchers still needed a way to connect one bacterial transistor to another. For this, they created three relay strains of Pantoea agglomerans. These bacterial relays translate the OHC-14 signal into an output that can be fed into another transistor.

This effectively allows the researchers to “wire” the bacterial transistors together, similar to how components are connected in an electronic circuit. 

The researchers created the circuits by printing colonies of bacteria onto plates containing agar, a growth medium used to grow microorganisms. Each colony was printed about 5 millimeters from the nearest colony. This arrangement allows the signal to travel to the next colony in a controlled direction. 

So, instead of wires carrying electricity, the circuit uses bacterial colonies and molecular signals to move information.

The Bacteria Can Perform Calculations

This is where the experiment gets particularly interesting. The researchers demonstrated bacterial transistors capable of performing several logic operations, including “multi-input,” “or,” and “imply” gates. They also combined the components to build more complicated circuits that could add two signals, process multiple signals at the same time and work as a demultiplexer. 

The largest circuit demonstrated by the team contained 24 bacterial colonies and was capable of adding two inputs together.

“This work shows that we can get toward more complicated functions by linking up simpler functions in individual cells,” Voigt says. “Computationally, there’s nothing that your iPhone can do that these circuits couldn’t do.” 

But there is an important catch.

The bacterial circuit is extremely slow compared with an electronic computer. Each calculation takes about eight hours. However, the researchers say that speed could still be useful for biological applications, where an overnight calculation can be fast enough compared with the much longer timescale of plant growth. 

Why Put A Computer Circuit On A Plant?

The researchers aren’t trying to make bacteria compete with smartphones or laptops. Instead, their goal is to bring computational capabilities directly into biology.

The team hopes that these bacterial circuits could eventually coat plant leaves or roots and help plants sense and respond to environmental conditions such as drought or pest attacks. 

“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 says. 

This could have interesting applications in agriculture. For example, a circuit placed around plant roots could potentially detect different types of stress. Once a particular signal is detected, the circuit could trigger a biological response, such as synthesizing a fungicide. 

Why Did MIT Use Different Bacterial Strains?

There is a reason the researchers did not simply put the entire circuit inside one bacterial cell. In traditional synthetic biology, scientists often engineer individual cells to contain multiple components that work together. But adding too many components can make the system more complicated and can put a burden on the cell’s machinery. 

MIT’s approach divides the work between different bacterial strains.

One type of cell works as a transistor. Other cells act as relays. These components can then be connected to build increasingly complicated circuits. It is similar to building a team where each member has a specific job instead of asking one person to do everything.

From Bacteria To ‘Living’ Computing Systems

The MIT research does not mean that bacteria are replacing computers. Instead, it demonstrates that living cells can be engineered to perform specific computational functions and connected together to create larger biological circuits. 

The researchers’ ultimate vision is particularly interesting: biological circuits could potentially live alongside plants, sense changes in their environment, process those signals and trigger a response.

That could turn bacteria from simple microorganisms into programmable biological components - tiny living parts of a circuit that can help plants detect and respond to the world around them.