Spores provide intimations of immortality
Scientists revive spores dormant for million of years, bolstering notion that life could exist elsewhere.
Out of a lab in Pennsylvania comes an old salt's tale of survival.
This week, West Chester University biologist Russell Vreeland and two colleagues report reviving and growing bacteria from 250-million-year-old salt crystals. The work shatters previous records for waking bacterial Rip Van Winkles.
In the process, some researchers say, it raises deep questions about whether dormant bacteria are "essentially immortal" and bolsters notions of finding evidence for primitive life on other planets or in meteorites that land on Earth.
For decades, the quest to find and revive bacteria has been marked by frustration.
Since the 1960s, various scientists have claimed to have discovered bacteria in salt formations ranging from 195 million to 650 million years old. But many researchers dismissed the claims, arguing that the samples were really bacteria that entered the formations later and that vital molecules, such as DNA, couldn't last for millions of years.
Five years ago, however, biologist Raul Cano at the California Polytechnic Institute in San Luis Obispo offered convincing evidence that he and a colleague had revived dormant bacteria, or spores, from a bee encased in amber for some 25 million years.
Yet amber typically dates back only about 400 million years. Salt deposits hold the potential for older finds.
Dr. Vreeland's bacteria - drawn from tiny water bubbles in salt deposits in New Mexico - could shed light on a number of issues.
For one, they could theoretically let scientists track the evolution of bacteria by studying genetic material from these ancient bacteria and comparing it with modern strains. Vreeland's initial genetic studies of the bacteria he found indicate that they are relatives of a salt-loving strain found in the Dead Sea.
Yet these creatures could also influence the debate on extraterrestrial life.
For example: Mars last had liquid water about a billion years ago. Could anything survive Mars's billion-year drought?
"This organism puts us 25 percent of the way there," Vreeland says.
Closer to home, he notes that meteorites that fell in Monahans, Texas, during the summer of 1998 hold salt crystals with small pockets of trapped water. He and his team are working with the owners to search the crystals for spores.
Finding spores in a meteorite would likely revive the notion that life on Earth may have been affected by - and perhaps originated with - bacteria that arrived from space via debris that enters Earth's atmosphere.
Called "panspermia," the notion has enjoyed a "small comeback lately," says Michael Yarus, a microbiologist at the University of Colorado in Boulder.
The modest uptick in panspermia's stock came when researchers at Stanford University and NASA found what they interpreted as fossilized evidence of microbial life in a meteorite that came from Mars.
"In that context, this could be a significant result," Dr. Yarus says of Vreeland's work. After all, researchers have calculated that a chunk of rock knocked from Mars might take millions of years to reach Earth.
Perhaps the biggest puzzle the bacteria present is their sheer ability to survive. "If these results are true, it's remarkable how robust these spores are," says R. John Parks, a geomicrobiologist at Britain's Bristol University.
Part of the reason may lie in packaging. Surrounded by water, then by the salt crystal, the spores are "double-sealed for freshness," he quips.
Even so, he adds, molecules like DNA or those that make up cell walls "aren't supposed to last that long."
Researchers had thought that the molecules' natural vibrations, as well as the radioactivity naturally occurring in salt, would destroy the chains of molecules that allow the spores to regenerate.
In principle, researchers should be able to find yet older specimens - a quest on which Vreeland says his team is already embarked.
(c) Copyright 2000. The Christian Science Publishing Society