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Materials

Engineered bacteria build microstructures on their own

Microbe-built domes coated with gold nanoparticles can serve as simple pressure sensors

by Michael Torrice
October 16, 2017 | APPEARED IN VOLUME 95, ISSUE 41

Credit: Nat. Biotechnol.
Synthetic biologists grew engineered bacteria on a porous membrane sitting on top of agar gel loaded with nutrients (top, left). The nutrients in the gel diffused through the membrane’s pores to help the bacterial colonies grow. As the colonies grew, they self-assembled a dome out of proteins (top, right, red). By varying the pore size and hydrophobicity of the membrane, the researchers could control the growth of the colonies and, as a result, the shape of the protein domes. For example, increasing the pore size led to wider domes with a higher contact angle to the membrane surface (bottom). Level of protein expression goes from low (blue) to high (red).

Inside the genomes of mollusks sit instructions on how to build their shells. Synthetic biologists want to learn how to write such genetic instructions so they can program cells to construct novel inorganic structures for devices such as biosensors and self-healing electronics.

Now, a team of researchers has engineered Escherichia coli to self-assemble gold-coated domes that can be used as simple pressure sensors (Nat. Biotechnol. 2017, DOI: 10.1038/nbt.3978).

Previous attempts to achieve engineered self-assembly have relied on researchers laying down molecular cues to coax microbes to construct patterns in desired shapes, says Megan N. McClean of the University of Wisconsin, Madison, who was not involved in the work. This group’s work, she says, demonstrates that “all of the information, in terms of how you want the community to develop into a spatial pattern, can be contained within individual cells themselves.”

Lingchong You of Duke University and colleagues packed that information into a circuit of genes that controls production of a modified protein called curli, which self-assembles into fibers and binds gold nanoparticles. The researchers found that with the genetic circuit, the bacteria produced curli only at the exterior of their colonies, leading the microbes to construct a curli-based dome over themselves.

Adding gold nanoparticles to the colonies produces domes that can be pressed together, top to top, to form a pressure sensor. Pushing on the domes increases their electrical connections, allowing the team to measure applied pressure via current flow between the domes.

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