Is silicon-based life possible?
For the first time, researchers have succeeded in enhancing and programming an enzyme to make silicon-carbon bonds – something that usually does not happen in nature and which up to know only chemists could do in the lab.
The study, conducted at the California Institute of Technology (Caltech, US), was published last week in the journal Science. To achieve the remarkable feat, the team of researchers used a technique called Directed Evolution which was pioneered by the senior author of the paper – Frances H. Arnold – in the early 1990s. In the direct evolution process, the DNA coding of the enzyme that scientists want to enhance is mutated over and over. The resulting enzymes are then tested for the desired trait, isolated and mutated again and again until the ‘best performing’ enzyme for the selected trait is created.
Specifically, the researchers at Caltech isolated and ‘bred’ the enzyme cytochrome c from the bacterium Rhodothermus marinus, which is found in hot springs in Iceland. They mutated the DNA coding and only after three rounds of mutation they were able to create a version of the enzyme which could selectively make silicon-carbon bonds fifteen times more efficiently than any other catalyst invented by chemists.
This result is remarkable. Carbon and silicon are chemically very similar; they sit on top of one another in the IV group of the periodic table of elements, which means they have the same number of valence electrons and hence very similar chemical/reaction properties. For this reason, scientists have long speculated whether silicon-based – rather than carbon-based – life could have evolved on Earth, especially since silicon is the second most abundant element (27%) in the Earth’s crust after oxygen (46%), while carbon is relatively quite rare (0.18%). This study proves that living bacteria can indeed create silicon-carbon bonds.
Does this mean that life could evolve using silicon bonds as building blocks? Arnold says that is up to nature. “This study shows how quickly nature can adapt to new challenges,” she said. “The DNA-encoded catalytic machinery of the cell can rapidly learn to promote new chemical reactions when we provide new reagents and the appropriate incentive in the form of artificial selection. Nature could have done this herself if she cared to.”
If anything, the study shows how resilient life is, and how flexible nature can be to exploit any resource available in the environment. It also gives us awareness about how potentially diverse biochemistry could be in other worlds were life could have evolved differently than on Earth. Moreover, the research has immediate practical applications: the modified enzyme is a more efficient alternative to current expensive and toxic catalysis techniques for the production of organosilicon compounds. These are molecules with silicon-carbon bonds which are widely used in pharmaceuticals as well as in agricultural chemicals, paints, semiconductors, and computer and TV screens.
Here is a link to the video explaining the research findings.
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