[Image above] Credit: caltech; YouTube
Here on earth, carbon is abundant. Silicon is abundant.
Yet carbon–silicon bonds are surprisingly absent in nature on our planet.
But that doesn’t mean that those bonds are absent from our everyday lives. Organosilicon compounds are everywhere around us—pharmaceuticals, agricultural chemicals, paints, semiconductors, and computer and TV screens, for just a few examples—but nearly all of those instances are formed synthetically.
And like many industrial techniques, synthetically forming carbon–silicon bonds is an expensive process that also yields harmful waste byproducts. Wouldn’t be so much easier if nature just formed those bonds for us?
With a little coaxing, it seems that nature can.
Researchers at California Institute of Technology (Pasadena, Calif.) are the first to report that, using directed evolution, they have convinced bacteria to biologically produce carbon–silicon bonds much more efficiently than synthetically catalyzed chemical reactions.
“No living organism is known to put silicon–carbon bonds together, even though silicon is so abundant, all around us, in rocks and all over the beach,” Jennifer Kan, postdoctoral researcher and lead author of a new study published in Science, says in a CalTech news release.
Similar to artificial selection, the process of directed evolution uses random mutations to create and select for traits of interest. In this case, the CalTech researchers mutated a particular enzyme of interest to have the ability to form silicon–carbon bonds.
“It’s like breeding a racehorse,” Frances Arnold—Caltech’s Dick and Barbara Dickinson Professor of Chemical Engineering, Bioengineering and Biochemistry; director of the Donna and Benjamin M. Rosen Bioengineering Center at Caltech; and principal investigator of the new research—says in the release. “A good breeder recognizes the inherent ability of a horse to become a racer and has to bring that out in successive generations. We just do it with proteins.”
The scientists started with a promising enzyme from Icelandic hot spring bacteria Rhodothermus marinus called cytochrome c.
Cytochrome c “normally shuttles electrons to other proteins, but the researchers found that it also happens to act like an enzyme to create silicon-carbon bonds at low levels,” according to the press release.
Serially mutating, screening, and selecting for bacteria with successively enhanced carbon–silicon bonding ability eventually provided the scientists with bacteria that could form silicon–carbon bonds 15 times more effectively than synthetic catalysts.
But the implications stretch beyond industrial synthesis, too—scientists have previously speculated that silicon could be alternative basis for life due its molecular similarity to carbon.
Watch this short CalTech video to hear more from the scientists themselves.
[Image above] Credit: caltech; YouTube
The paper, published in Science, is “Directed evolution of cytochrome c for carbon–silicon bond formation: Bringing silicon to life” (DOI: 10.1126/science.aah6219).