Scientists have built living circuit boards by printing bacterial cells into carefully arranged patterns, creating reconfigurable biological computers that can perform logic operations without altering their genetic code. In a study published in Nature Chemical Biology, researchers designed strains of Pantoea agglomerans to behave like molecular transistors, then combined them with relay strains that direct chemical signals across a solid surface. By changing where the cells are placed, the team produced different computational systems, including multi-input, multi-output logic, a demultiplexor, a half-adder and a full-adder. The work suggests that complex biological computation may be assembled not only through genetic engineering, but also through the physical organization of living cells.
The researchers drew inspiration from pass transistor logic, or PTL, a style of electronic circuit design in which transistors regulate the movement of signals between different parts of a system. In conventional electronics, those signals are electrical currents. In the bacterial circuits, they are small molecules that diffuse through the environment and activate genetically encoded responses. Each engineered cell interprets a chemical input and produces a chemical output, allowing the cells to function as biological components in a larger circuit. The approach separates the design of the cellular parts from the design of the overall system: the same strains can be rearranged into new circuits simply by changing their spatial pattern.
This distinction is important because natural cellular communication networks are extraordinarily difficult to reprogram. A single biological response can involve receptors, transcription factors, feedback loops and multiple interacting signaling pathways. Changing one genetic component may therefore produce unexpected effects elsewhere in the cell. Instead of attempting to rebuild an entire regulatory network for every new function, the team created a limited set of bacterial parts, each carrying out a defined operation. Those parts could then be connected externally, much as electronic components are wired together on a circuit board. The result is a form of biological engineering in which geometry becomes part of the programming language.
The central components are two bacterial transistor strains, one designed to act as an N-type transistor and the other as a P-type transistor. In electronic systems, N-type and P-type devices respond differently to control signals and can be combined to implement switching behavior. In the bacterial version, the input and output are molecular rather than electrical. A small molecule supplied to an engineered cell activates a genetic program, and the cell responds by producing or releasing another signaling molecule. The output can then affect a neighboring strain, creating a chain of biochemical events. Together, these cells provide the basic switching functions required to construct logic gates.
The system also includes three relay strains that solve a major problem in biological circuitry: molecular diffusion is naturally multidirectional. If a signal spreads freely, it can activate cells that were not intended to receive it, causing interference between different parts of the circuit. The relay strains convert diffusion into a more controlled, unidirectional flow. They receive one molecular signal, process it and pass a distinct signal to the next stage. In this way, the relays act as biological wiring, helping establish an ordered path through the circuit while reducing unwanted cross-talk. Their inclusion means that the researchers do not need to genetically redesign every transistor whenever a new circuit is required.
To assemble the systems, the researchers used an acoustic liquid handler, an instrument capable of transporting tiny volumes of liquid through sound-generated droplets. The device printed patterns of the five bacterial strains onto a solid surface, placing each cell type at a defined location. Once deposited, the cells formed the living elements of the circuit, while the spaces between them allowed chemical signals to move from one component to another. The printing process therefore served as both fabrication and programming. A new computational function could be created by changing the arrangement of the same five strains, rather than by constructing a new collection of engineered genomes.
This spatial reconfiguration enabled the team to build circuits with several inputs and outputs, allowing multiple molecular signals to be processed simultaneously. They also created a demultiplexor, a system that directs one input signal toward one of several possible outputs depending on a control signal. Such a function is common in electronic communication systems, where it is used to route information. In the bacterial platform, the same principle is implemented through the selective activation of cellular pathways and relay chains. The demonstration shows that the cells are not limited to simple on-or-off responses; they can be organized into architectures that manage signal routing and information flow.
The researchers further demonstrated arithmetic functions by constructing a half-adder and a full-adder. A half-adder combines two binary inputs and produces a sum and a carry output. A full-adder performs the same operation while also accepting a carry input from an earlier stage, making it possible to connect multiple units for larger calculations. In the living circuits, binary information is represented by the presence or absence of molecular inputs, while the output states are determined by the activity of the engineered bacteria. These demonstrations are particularly significant because addition requires coordinated processing of several signals and the generation of more than one output, rather than a single response.
The platform points toward a different way of thinking about synthetic biology. Instead of viewing cells only as programmable machines whose behavior must be encoded entirely in DNA, the study treats groups of cells as modular systems whose behavior depends on both genetics and physical arrangement. The approach could make complex circuits easier to prototype, since researchers can test new configurations without repeatedly editing bacterial genomes. It may also offer a route to biological devices that operate on surfaces, where chemical signals can be detected, routed and transformed by living materials. Significant challenges remain, including improving signal insulation, controlling variability between cells and maintaining circuit performance over time. Even so, the work shows that only five cell types, each carrying a relatively simple task, can be assembled into a surprisingly broad range of computational operations. By turning bacterial colonies into printable, reconfigurable circuit boards, the researchers have brought biological computing closer to the logic of engineering.
Subject of Research: Reconfigurable bacterial circuits and living circuit boards based on pass transistor logic.
Article Title: Living circuit boards built by printing bacterial transistors
Article References: Doosthosseini, H., Chen, H. & Voigt, C.A. “Living circuit boards built by printing bacterial transistors.” Nature Chemical Biology (2026). https://doi.org/10.1038/s41589-026-02300-3
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41589-026-02300-3
Keywords: synthetic biology, bacterial transistors, biological computing, living circuit boards, pass transistor logic, cellular communication, molecular circuits, Pantoea agglomerans, genetic engineering, biofabrication
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