Bacteria locked inside salt crystals have just broken the world record for longevity. In the 19 October issue of Nature, researchers describe how they isolated microbes from a 250-million-year-old rock formation. The discovery suggests that some bacteria are practically immortal, says the study's lead author, microbiologist Russell Vreeland of West Chester University in Pennsylvania.
Vreeland decided to search for ancient bacteria after a student asked him how long microbes could live. But he didn't look in amber, as had a group of researchers that retrieved live 27-million-year-old bacteria in 1995; instead, he tried salt crystals, which, like amber, can create very stable and protective environments. As salt crystals form, they trap small pockets of brine in which microbes are shielded from the ravaging effects of oxygen and other gases.
Vreeland and his colleagues searched in salt rocks whose age had been well established by other researchers: the Permian Salado Formation, which has been dated both from fossils and by radiometric studies. They collected 90 kilograms of samples from as deep as 560 meters underground in a pilot nuclear waste facility outside Carlsbad, New Mexico.
To rule out contamination by modern bacteria, they first rejected all samples that appeared to be damaged in any way. After gently removing the dirt from 53 remaining samples, they took them into a medical clean room. They washed the crystal surfaces with concentrated bleach and lye. Then they bored tiny holes into the crystals with sterilized drills to reach a pocket of trapped brine.
When placed in growth media, fluid samples from two crystals yielded a total of four bacterial strains. Thus far, the researchers have characterized only one, a rod-shaped Bacillus similar to a microbe that lives in the Dead Sea. Bacillus bacteria form spores when faced with harsh conditions, and that's probably how they survived for millions of years, Vreeland says.
It can be difficult to convince skeptics about ancient bacteria, but Vreeland's group is doing that. "They make a compelling argument," says microbiologist Raul Cano of the California Polytechnic State University in San Luis Obispo. The work needs to be replicated, but the microbes "have a good chance of being that old," Cano says.
Ancient bacteria from another extreme environment: deep-sea vents