Cyanide—Poison or Bringer of Life?

Terrestrial biology may have gotten a boost from an unlikely source.

We're taught to fear cyanide, but context is everything.

Cyanide is hardly known for its life-friendly attributes—in fact, it’s most often associated with death by poisoning. But a new study by Karen Smith from Boise State University and colleagues suggests that it may also have played a major role in the origin of life on Earth. Not only did the researchers find cyanide in carbonaceous chondrites—meteorites thought to have originated in the early Solar System—but the particular compounds of cyanide they found are similar to the earliest enzymes used by bacteria and single-celled organisms known as archaea.

Called hydrogenases, these particular types of enzyme are critical for microbes to catalyze molecular hydrogen. Most scientists believe that the oxidation of hydrogen was the first metabolism of life on Earth. But it could not have happened without the presence of compounds that activated the chemical reactions.

The scenario goes as follows: Carbonaceous chondrites would have fallen on the early Earth in shallow ponds, streams, and puddles. In those settings, water would have leached out of the cyanide, which would in turn have undergone several reactions to form a number of biologically important compounds, eventually turning into enzymes critical for hydrogen metabolism.

Maybe it shouldn’t surprise us that a poison could be useful to life. Cyanide’s very toxicity shows that it plays a role in many biological reactions. And it serves as yet another reminder that we may need to get over our preconceptions about which environments might be beneficial to life on other worlds, and which might be harmful.