Was an ancient bacteria awakened by an industrial accident?

The bacteria in question lives at the bottom of Lake Peigneur in southern Louisiana. The land beneath the lake is rich in natural resources. In 1980 it contained a mine producing rock salt, while a drilling rig operated by Texaco roamed the surface in search of oil. But on November 20, the two operations coincided, coincidentally and brilliantly. The oil rig’s drill penetrated the third level of the salt mine, creating a drain in the lake bed.

Over the next few days the man-made sinkhole swallowed an oil rig, 11 barges, a tugboat, 35 hectares of land and part of a house. A canal that drained the lake into the Gulf of Mexico began backing up as the water level dropped, creating the highest waterfall in Louisiana for a time, while dirty geysers began to erupt from the mines. Somehow all the 50 people working in the mine managed to get out from the rising flood waters.

An official report could not determine whether the oil rig was drilling in the wrong place, or whether the mine maps were incorrect. Either way, the disaster created an entirely new environment. The water flowing into the mine contained less than 2% salt. But rock salt dissolves easily in water. When Dr. Vreeland at the University of New Orleans was allowed access to a section of the flooded mine in 1987, he found that the water contained 32% salt, about nine times more than seawater.

That much salt would be lethal for most creatures. But Dr. Vreeland found one species of bacteria in his samples, one of a salt-loving group called Halobacteria. This worm grew best in water containing 18% salt – and died when the concentration dropped below 10%. Since the bacteria could not survive in the lake, how did it get into the mine water?

With only access to a small laboratory and comparatively few resources, Dr. Vreeland decided to put an end to the mystery and move on to other projects. However, during a trip to China in 2016, he met Dr. Chui, another expert on salt-loving microbes, and decided to return to his cold case.

In the intervening years, scientists have discovered that some bacteria have extraordinary powers of self-preservation. When times are tough they may enter a type of stasis, whereby all biological activity ceases until conditions improve. The salt beneath Peganur Lake was formed by the evaporation of previous reserves of salty water. Some of the salt is 125 million years old, meaning it was laid down during the heyday of the dinosaurs. The researchers suggest that the new species is antediluvian both literally and metaphorically. It was there before the mine flooded, trapped in pockets of water within salt crystals – and it may have been there for millions of years.

It is difficult to test how long bacteria can live in suspended animation, as experiments cannot last more than a few decades. But Dr. Vreeland claimed in Nature in 2000 that he and his colleagues had succeeded in reviving another salt-loving bacterium dating back 250 million years. A study published last year argued that, under certain circumstances, a particularly resilient species called Deinococcus radiodurans might be able to manage stagnation for up to 300 million years.

And Dr. Vreeland explains that the conditions of the salt mine may have helped this latest species live out the ages in relative safety. One problem that hibernating organisms face is the gradual accumulation of damage in their DNA. Oxygen is a source of such damage. But this element is not present inside rock-salt crystals, and is only very slightly soluble in salt water. Ultraviolet light is another hazard, but none penetrates underground.

Background radiation can also damage the genome. But the only radioactive atom found in salt water is potassium-40. With a half-life of over a billion years, it is only mildly radioactive. And bacteria that live in harsh environments, including Halobacteria, have abundant DNA-protecting proteins to prevent damage. Now, due to a human mistake, Dr. Vreeland’s bacteria has been given an entire mine to live in, where it can finally reap the rewards of its amazing patience.

© 2023, The Economist Newspaper Limited. All rights reserved.

From The Economist, published under license. Original content can be found at www.economist.com

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Published: Jan 16, 2024, 06:02 PM IST