11 October 2017

Bacteria create micro sensors

Sergey Syrov, XX2 century

Researchers from Duke University (USA) programmed bacteria in such a way that they built a useful device – a pressure sensor.


The black dots on the micrograph are gold nanoparticles that are captured by a protein on the surface of a bacterium. A snapshot from the press release of Bacteria Self-Organize to Build Working Sensors – VM.

When a bacterial colony grows, taking the form of a hemisphere, a synthetic biological chain triggers the production of a certain type of protein throughout the colony. Bacteria get the opportunity to include inorganic materials in their structures, in this case gold nanoparticles were used. As a result, a conductive shell is formed around the bacterial colony, the size and shape of which can be adjusted by growing bacteria in various conditions.

The result of the experiment is a device that can be used as a pressure sensor. This shows that it is possible to create working devices using this process.

Previously, experiments have already been conducted, during which various materials were successfully created using bacterial processes. But all of them took place under conditions of strict control of bacterial growth. The work of Duke University scientists demonstrated the production of a composite structure through the programming of the cells themselves and the control of bacterial access to nutrients, but without physically limiting the possibility of colony growth in three dimensions.

The results of the study were published on October 9 in the journal Nature Biotechnology (Cao et al., Programmable assembly of pressure sensors using pattern-forming bacteria).

"The technology allows us to grow a functional device from a single cell," says one of the authors of the work, Lingchong Yu (Lingchong You). "In principle, this is no different from programming a cell from which a tree will grow."

Nature is full of examples when organisms combine organic and inorganic substances to obtain the highest quality materials. Mollusks grow shells consisting of calcium carbonate and a small amount of organic components. As a result of the organization of the microstructure, the shell turns out to be three times tougher than could be achieved by manufacturing it only from calcium carbonate. For examples, it is not necessary to go to the seashore – our own bones are a mixture of collagen (organic) and inorganic minerals.

The use of bacteria's abilities for construction can be much more efficient than the production processes currently used. In nature, organisms often use raw materials and energy extremely sparingly. In such an artificial system, the creation of "instructions" for growing various figures and models can be much cheaper and faster than the production of new stamps and molds required in traditional production.

"Nature is a master of making structured materials consisting of living and inanimate components," Yu says, "But the natural program for creating self–organizing models is extremely complex. Our work, however, is proof of the principle that this is not impossible."

A synthetic biological chain is a package of genetic instructions that researchers have embedded in the DNA of a bacterium. First, the bacteria produce the protein T7RNAP, which then activates its own production (positive feedback begins to work). The bacterium also produces small signaling AHL molecules.

During the process of cell growth and reproduction, the concentration of AHL molecules reaches a critical concentration threshold, at which the production of two more proteins is started - lysozyme T7 and amyloid protein of the surface of microorganisms – curli. The first suppresses the production of T7RNAP, and inorganic compounds can attach to the second.

The dynamic interaction of feedback loops causes the bacterial colony to form a domed shape, growing until the food runs out. A biological "Velcro" is produced on the outside of the dome, capturing gold nanoparticles.

The researchers learned how to change the size and shape of the resulting dome by controlling the properties of the porous membrane on which the bacteria were planted. The size of the pores or the water–repellent properties of the membrane changed - this affects how much and how quickly the cells receive nutrients.

"We demonstrate one of the methods of manufacturing a three–dimensional structure based solely on the principle of self-organization," said Stefan Zauscher, a professor at Duke University. – This volumetric structure is used as a framework to create a device with certain physical properties. This approach is inspired by nature, and since nature doesn't do it by itself, we manipulate nature to do it for us."

To show how the described system can be used to manufacture working devices, the researchers used the resulting hybrid structures as pressure sensors.

Identical bacterial domes were grown on two substrate surfaces. Then the two substrates were stacked so that each dome was located opposite its counterpart.

Then each dome was connected to the LEDs via a copper wire. If the resulting structure is compressed, the domes press on each other, deformation occurs, leading to an increase in conductivity. This can be seen by changing the brightness of the LEDs.

According to the researchers, such technology can find many applications. The task of scientists is to learn how to program cells so that they form complex and pre–predicted structures.

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