Bacteria taught to bond carbon and silicon for the first time

Proteins solve problems. By guiding evolution along, scientists have created a protein that can bond carbon to silicon. This innovation could transform how we make a broad array of products, from drugs to LED lights, semiconductors and computer screens.

Silicon is the second most abundant element in Earth’s crust, but it doesn’t naturally bond to carbon. That means manufacturers must turn to artificial methods to make compounds combining the two, which are called organosilicons and feature in materials including adhesives and silicone coatings.

It would be more sustainable and perhaps cheaper to create the same bonds with biology, says Frances Arnold at the California Institute of Technology in Pasadena. But until now, scientists have been unable to find or produce such a reaction in nature.

She and her colleagues have now unveiled a protein that does the job. The team created it using a process of artificial selection called directed evolution, and it outperforms all other existing methods of bonding the two elements.

“It’s a wonderful demonstration of how rapidly nature can adapt to solve problems,” says Arnold. “All of this diversity in the natural world is poised to do entirely new chemistry if you provide these new niches, so to speak.”

Life, but not as we know it

Arnold and her team started with a protein found in the genomic sequence of Rhodothermus marinus, a bacterium that was originally discovered in Icelandic hot springs. Called cytochrome c enzyme, it typically transports electrons around the cell. But early lab tests suggested that with a little direction, it might be able to create the types of bonds that the researchers were looking for.

They synthesized the protein in E.coli and modified it by randomly mutating its DNA coding. Each time, they selected the most promising candidates and mutated them again. After three rounds of mutations, the protein could bond silicon to carbon 15 times more efficiently than any synthetic catalyst. It’s also far more reliable and produces fewer unwanted byproducts, and because it is used to tough geothermal environments, it is hardy. “You can boil this protein and it still functions,” says Arnold.

“This is something that people talk about, dream about, wonder about,” says Annaliese Franz at the University of California, Davis. She imagines the process could be particularly useful for drug discovery, as organosilicons are used in some pharmaceuticals. “Any pharmaceutical chemist could read this on Thursday and on Friday decide they want to take this as a building block that they could potentially use.”

The research may also help us answer questions about what silicon-based life forms would look like, says Arnold – here or on another planet. “One can start to dream about what happens when you put silicon into life.”