Gürol Süel points to an oval image on a large screen. It’s a video of a spore that periodically changes color.
“It’s counting every time it encounters food. It’s summing those signals and it gets brighter and brighter, and that means it’s getting closer to waking up,” said Süel, a professor of molecular biology at UC San Diego.
The spore is what’s become of a bacterial cell that has encountered harsh conditions. It’s not exactly dead, but Suel said it is in a state of dormancy where the common needs and functions of a living organism are not to be seen.
“The spore appears to be dead,” Süel said. “There’s no metabolism, which is how food gets converted to chemical energy by the cell. There’s no gene expression. The spore isn’t growing. It isn’t replicating or making more of itself.”
Yet, the spore survives.
A paper co-written by Süel and published in the journal Science shows this “undead” organism is able to monitor and respond to the presence of food, to determine when it’s time to rejoin the ranks of the living.
The notion of rising from the dead may still belong to the world of horror flicks and science fiction. But the spore’s resilient state of dormancy is so similar to being dead that it shows that life can be, at least, put on pause until environmental conditions improve and nutrients are available.
Another microscopic video shows spores “waking up” after repeated signals that food is present. Süel said the spore is a bit like a child, born from a bacterial cell that becomes a bacterium once again when conditions are right.
“So they take up water, and they start to do all the normal biological processes that we could expect, like metabolism starts, gene expression starts. And they become a fully living, regular bacterial cell,” he said.
Spores can survive for millions of years. This was shown by the discovery and revival of spores that once lived in the guts of an ancient honeybee and were preserved in amber. In fact, Süel said spores have been taken to the International Space Station, where they provided proof they can survive in outer space.
Surviving spores may be the best way to explain how extraterrestrial life could come to Earth.
“One of the ideas of how life emerged on our planet is that maybe it hitchhiked on an asteroid and crash-landed on our planet,” Süel said. “But to do that, you would have to have some kind of living material that survived that journey.”
It might have been a spore. Süel said that our search for life on other planets may lead us to discover spores, maybe on Mars, that aren’t actually dead. They are just waiting to be served dinner.
