Designer bacteria build carbon-silicon materials for the first time

Scientists have genetically engineered bacteria to make a protein that squishes silicon and carbon together long enough for them to stick to one another — forming a bond that, until now, only chemists had managed to create. If scientists can teach these bacteria to produce the carbon-silicon molecules used to make semiconductors, pesticides, and even silicone breast implants, it could make manufacturing these products easier.

The chemical factories of the future

Carbon and silicon are reluctant to stick together, so making them bond takes time. To form these bonds, scientists bathed genetically engineered bacteria in a nutrient broth that included silicon and carbon compounds. The bacteria absorbed these compounds through their outer membrane, their version of our skin. Inside the cells, a lab-designed protein pressed the molecules tightly together until the carbon and silicon atoms formed a bond, creating carbon-silicon, or organosilicon, compounds. The bacteria then sweated these compounds back out into their soupy surroundings, according to a paper recently published in the journal Science.

Right now, we don’t know if we can use the molecules that these bacteria produce. With 20 different combinations of raw materials, the bacteria produced 20 different organosilicon molecules — 19 of which had never been seen before. But the results close “a crucial gap between biological and chemical” reactions, write the authors of an outside analysis of the work also published in Science. “Beautiful work, creating new chemistry,” Nobel prize-winning chemist Roald Hoffmann told Nature.

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Creatures like algae, rice, and marine sponges incorporate silicon compounds into their bodies. But until now, as far as scientists know, no living thing has ever made molecules where silicon and carbon connect. Only chemists have done this, by adding expensive metals to the mix that can speed up the chemical reaction so the link actually takes. It’s like adding an ingredient to glue to make it dry faster when you’re trying to stick the handle back on a mug.

Frances Arnold, a molecular biologist at the California Institute of Technology, thought that with the right modifications, proteins might be even better at forcing these reluctant chemical bonds between silicon and carbon. That’s because in cells, certain proteins can hold atoms close enough to each other to make it easier for them to stick together. It’s like gluing that broken mug: the handle won’t stick to the cup if they’re too far apart. But press them together, and the glue will bond the two pieces.

“This innovation machine that’s evolution.”

“Life speeds up all these chemical reactions in the body,” Arnold told The Verge. “We want to make cells into the chemical factories of the future.”

So Arnold and her colleagues looked for a protein with some natural aptitude for sticking carbon and silicon together by screening bacteria from all over the world. They found it in the briny waters of Iceland’s hot springs. As long as there were specific human-made, silicon-containing raw materials around, a protein inside these heat and salt-loving bacteria could fit silicon and carbon together.

Those specific bacteria don’t thrive in the lab, but E. coli bacteria do. So the scientists plopped several forms of the protein inside E. coli, using genetic engineering, and then selectively ‘bred’ the E. coli that were best at producing these organosilicon molecules — just as a breeder would selectively breed dogs for certain traits. They wound up with a generation of E. coli possessing a form of the protein that’s even better at joining carbon to silicon than chemists are. “This innovation machine that’s evolution, we can use it to do all sorts of interesting things,” Arnold says.