By programming bacteria with a synthetic gene circuit, researchers at Duke University were able to create a working pressure sensor.
As the bacterial colony grew, the gene circuit triggered the production of protein that recruited inorganic materials. When supplied with gold nanoparticles by researchers, the system formed a golden shell around the bacterial colony.
The study appears today in Nature Biotechnology.
"This technology allows us to grow a functional device from a single cell," said Lingchong You, the Paul Ruffin Scarborough Associate Professor of Engineering at Duke.
Harnessing such construction abilities in bacteria would have many advantages over current manufacturing processes. In nature, biological fabrication uses raw materials and energy very efficiently. In this synthetic system, for example, tweaking growth instructions to create different shapes and patterns could theoretically be much cheaper and faster than casting the new dies or molds needed for traditional manufacturing.
The genetic circuit is like a biological package of instructions that researchers embed into a bacterium's DNA. The directions first tell the bacteria to produce T7 RNA polymerase (T7RNAP), which then activates its own expression in a positive feedback loop. It also produces a small molecule called AHL that can diffuse into the environment like a messenger.
As the cells multiply and grow outward, the concentration of the small messenger molecule hits a critical concentration threshold, triggering the production of two more proteins, T7 lysozyme and curli. The former inhibits the production of T7RNAP while the latter acts as sort of biological Velcro that can latch onto inorganic compounds.
The dynamic interaction of these feedback loops causes the bacterial colony to grow in a dome-shaped pattern until it runs out of food. It also causes the bacteria on the outside of the dome to produce the biological Velcro, which grabs onto gold nanoparticles supplied by the researchers, forming a shell about the size of your average freckle.
The researchers were able to alter the size and shape of the dome by controlling the properties of the porous membrane it grows on.
"We're demonstrating one way of fabricating a 3-D structure based entirely on the principal of self-organization," said Stefan Zauscher, the Sternberg Family Professor of Mechanical Engineering & Materials Science at Duke. "That 3-D structure is then used as a scaffold to generate a device with well-defined physical properties. "
"In this experiment we're primarily focused on the pressure sensors, but the number of directions this could be taken in is vast," said Will (Yangxiaolu) Cao, a postdoctoral associate in You's laboratory and first author of the paper. "We could use biologically responsive materials to create living circuits. Or if we could keep the bacteria alive, you could imagine making materials that could heal themselves and respond to environmental changes."