Researchers have discovered how to get bacteria to form biofilms that can combined with nonliving materials.
These "living materials" could allow scientists to reap the benefits of living cells and nonliving materials, a Massachusetts Institute of Technology (MIT) news release reported.
Live cells are able to "respond to their environment, produce complex biological molecules, and span multiple length scales," while nonliving materials can conduct electricity and generate light, the news release reported.
This technique could be used in applications such as solar cells and self-healing materials.
"Our idea is to put the living and the nonliving worlds together to make hybrid materials that have living cells in them and are functional," Timothy Lu, an assistant professor of electrical engineering and biological engineering said in the news release. "It's an interesting way of thinking about materials synthesis, which is very different from what people do now, which is usually a top-down approach."
The researchers employed E. coli bacteria because it naturally produces biofilms that contain "curli fibers"; these are amyloid proteins that help the bacteria bind to surfaces. The fibers are made up of modifiable protein subunits called CsgA. The subunits can be modified by adding protein fragments called peptides, which can capture nonliving materials such as gold nanoparticles.
The team was able to manipulate the bacteria to produce different types of curli fibers and different times which allowed them to employ certain properties such as "gold nanowires, conducting biofilms, and films studded with quantum dots, or tiny crystals that exhibit quantum mechanical properties," the news release reported.
In order to accomplish this the team disabled the cells' ability to produce CsgA and substituted it with an engineered genetic circuit that produces the protein; the circuit only released CsgA when a molecule called AHL was present. When the researchers allow AHL to be present the CsgA forms curli fibers that become surface-coating biofilms.
The team also engineered E. coli cells to produce CsgA with peptides made of amino acid histidine clusters when the molecule aTc was present. The two types of engineered cells could be grown in a colony, and would allow researchers to control the composition of the biofilm.
"If gold nanoparticles are added to the environment, the histidine tags will grab onto them, creating rows of gold nanowires, and a network that conducts electricity," the news release reported.
The cells were able to communicate with each other to determine the composition of these biofilms.
"It's a really simple system but what happens over time is you get curli that's increasingly labeled by gold particles. It shows that indeed you can make cells that talk to each other and they can change the composition of the material over time," Lu said. "Ultimately, we hope to emulate how natural systems, like bone, form. No one tells bone what to do, but it generates a material in response to environmental signals."
