Engineered living materials promise to aid efforts in human health, energy and environmental remediation. Now it can be highly built and customized with less effort.
Biologists and synthetic biologists at Rice University have introduced centimeter-sized slime-like colonies of engineered bacteria that self-assemble from the bottom up. They can be programmed to absorb pollutants from the environment or to stimulate biological reactions, among the many possible applications.
Creating self-engineered living materials — or ELMs — has been a goal of biologist Caroline Ajo Franklin long before she joined Rice in 2019 with a grant from the Texas Cancer Prevention and Research Institute (CPRIT).
“We’re making a substance out of bacteria that act like putty,” Ajo Franklin said. “One of the nice things about it is how easy it is to make, it just needs a little bit of movement, some nutrients and bacteria.”
A study was published this week in Nature Connections Details of in vitro creation of flexible and adaptable ELMs using Caulobacter crescentus as a biological building block. While the bacteria themselves can easily be genetically modified for different processes, designing them for self-assembly has been a long and complex process.
It involved engineering the bacteria to display and secrete the biopolymer matrix that gives the material its shape. C. crescentus actually produces a protein that covers its outer membrane like snake scales. The researchers modified the bacteria to express a version of this protein, which they call BUD (bottom-up de novo .).And the as in from scratch), with properties that are not only favorable for the formation of ELMs (termed BUD-ELMs) but also provide markers for future operation.
“We wanted to show that it’s possible to grow material from cells, like a tree growing from a seed,” said study lead author Sarah Molinari, a postdoctoral researcher in the Ajo-Franklin lab who has a PhD in Rice Systems and Synthetic and Physical Biology. Ph.D. a program. “The transformative aspect of ELM is that it contains living cells that allow the material to self-assemble and self-repair in the event of damage. Furthermore, it can be further engineered to perform non-native functions, such as the dynamic processing of external stimuli.”
Molinari, who received her Ph.D. In the lab of Rice biologist Matthew Bennett, he said the BUD-ELM is the most customizable example of an independently configured macroscopic ELM. “It shows a unique combination of high performance and sustainability,” she said. “Thanks to its modular nature, it can serve as a platform for the generation of many different materials.”
ELMs grow in a beaker in about 24 hours, according to the researchers. First, a thin crust forms at the interface between air and water, which results in the seeding of the material. Constant shaking of the flask encourages ELM to grow. Once it expands to a sufficient size, the material sinks to the bottom and does not grow further.
“We found that the vibration process affects the volume of the material we get,” said co-author Robert Tesorero Jr., Ph.D. Student in structural and physical systems and biology. “Partially, we are looking for the optimal range of materials that we can obtain in a beaker of about 250 mm in length. It is currently the size of a fingernail.”
“Reaching to the centimeter scale with a cell less than a micron in size means that they collectively organize more than four orders of magnitude, about 10,000 times larger than a single cell,” Molinari added.
She said their functional materials are strong enough to survive in a jar on a shelf for three weeks at room temperature, meaning they can be transported without refrigeration.
The lab demonstrated that BUD-ELM could successfully remove cadmium from solution and was able to perform biological catalysis, enzymatically reducing the electron carrier for glucose oxidation.
Because BUD-ELMs are marked for attachment, Ajo-Franklin said they should be relatively easy to modify for optical, electrical, mechanical, thermal, transport and catalytic applications.
“There’s a lot of room to play, and I think it’s the fun part,” said Tesoriero.
“The other big question is that while we love Caulobacter crescentus, it’s not the most popular baby on the scene,” said Ajo-Franklin. “Most people have never heard of it. So we’re really interested to see if these rules that we discovered in Caulobacter can be applied to other bacteria.”
She said ELMs could be particularly useful for environmental remediation in low-resource settings. C. crescentus is ideal for this because it requires fewer nutrients to grow than many bacteria.
“One of my dreams is to use the material to remove heavy metals from the water, and then when it reaches the end of its life span, pull out a small portion and immediately transplant it into a new material,” Ajo-Franklin said. “That we can do this with the least amount of resources is a really compelling idea for me.”
The research co-authors are graduate student Switha Sridhar, postdoctoral researcher Rong Kai, lab director Jayashree Suman of Rice, Kathleen Ryan of the University of California, Berkeley, and Dong Li and Paul Ashby of Lawrence Berkeley National Laboratory, Berkeley, California. . Ajo-Franklin is Professor of Biosciences and CPRIT Research Fellow in Cancer Research.
Defense Advanced Research Projects Agency, CPRIT (RR190063), Office of Naval Research (N00014-21-1-2362) and Office of Science, Office of Basic Energy Sciences, US Department of Energy (DE-AC02-05CH11231) research support.