MIT engineers have created a prototype of living transistors that use biological signals instead of electrical ones. The development is based on three strains of the bacterium Pantoea agglomerans, which carry signals through the circuit instead of electrons. A single computation takes about 8 hours, but the results of the study, published in the journal Nature Chemical Biology, demonstrate an unexpected potential for biotechnology. This is not about competing with silicon chips, but about embedding logic directly into living systems.
Christopher Voigt, head of MIT's Department of Biological Engineering and senior author of the study, explained that the team is not trying to replace traditional computers but wants to introduce computational control into biology. According to him, if bacteria are placed on a plant's root or the plant itself is performing computations, then a simple calculation overnight is fast enough relative to a growing season. Previous attempts in this field relied on enzymes and placed an entire circuit inside a single large cell, which severely limited the complexity of the resulting constructs.
Biological transistors operate on a different principle. As the authors of the work describe, they do not define the logic of the circuit but conditionally permit signal propagation. This approach allows biotransistors to be combined in different configurations and assembled into more diverse circuits. For the prototype, bacterial colonies were printed on miniature plates, positioned approximately 5 millimeters apart from each other. The mechanism is based on a family of molecules that has long been used in biochemical research. One molecule acts as a switch, the second serves as a target and indicates whether the switch is active. In the presence of the target molecule, the transistor produces an output molecule that is passed on to the next element in the chain.
Tests showed that the circuit is capable of performing a range of logic operations using just 5 strains, and the largest assembled construct combined 24 bacterial colonies. The technology has plenty of limitations: the colonies remain living organisms and grow and change over time, the operating speed is constrained by the natural diffusion of molecules between colonies, and the entire living computer functions for about 3 days. Such a development is no competitor to office machines, but applications in agriculture look entirely feasible. The circuit could be placed near plant roots to monitor stress conditions and autonomously respond to pests or other environmental threats.
Christopher Voigt noted that the work demonstrates the possibility of advancing toward more complex functions by linking simple functions in individual cells. From a computational standpoint, there is nothing a modern smartphone can do that these circuits could not. Despite the progress, practical application of the technology is still a long way off, and researchers still face numerous engineering challenges in increasing the operating speed and stability of biological components.