Row over ancient bacteria

The bacteria came from salt crystals in New Mexico

By BBC News Online science editor Dr David Whitehouse

An international row is brewing over claims that a strain of bacteria was brought back to life after having remained dormant in a rock crystal for 250 million years.

A new genetic analysis of the bacteria, called strain 2-9-3, suggests that it is too similar to modern bacteria to have come from the past.

In an article in the journal Molecular Biology and Evolution, researchers from Israel say that the rock crystal was contaminated.

But the original researchers are standing their ground, saying that their critics rely on shaky arguments and dubious logic.

Suspended animation

The bacteria were found last year in salt crystals buried almost 610 metres (2,000 feet) below ground in a mine in south-east New Mexico, US.

Strain 2-9-3 is not a contaminant. I estimate that its chances of being a contaminant are less than one in a million

Professor Russell Vreeland
West Chester University

In an experiment that was hailed as a breakthrough, the ancient bacteria were revived after having been trapped in a state of suspended animation for 250 million years, making them the world's oldest living things.

Previously, the world's oldest living things were thought to be 25-40-million-year-old bacterial spores found in a bee preserved in amber.

But, according to the authors of the latest report, Professor Dan Graur and Dr Tal Pupko of Tel Aviv University, Israel, the claims of 250 million-year-old bacteria are false: the bacteria are modern, they say.

The scientist behind the original claim, Russell Vreeland from West Chester University, Pennsylvania, is not happy with the new publication.

"I have read it," he told BBC News Online. "They asked me to review it for publication but refused to consider any of my comments or consider printing my response alongside the article."

To reach their conclusion, Professor Graur and Dr Pupko downloaded the genetic information about strain 2-9-3, sometimes called B. permians, from the GenBank directory on the internet. They then compared 2-9-3's genes with those of modern bacteria to see how different they were.

According to the molecular clock model, the more they differed, the greater the time difference between the two strains of bacteria. That is, the longer that 2-9-3 has existed, the greater would be the number of mutations it would have accumulated when compared with a bacteria alive today.

If strain 2-9-3 was very similar to modern bacteria it could not be all that old, the Israeli scientists believed.

They found that 2-9-3 was genetically almost identical to a "modern" species of common bacteria, S. marismortui.

"The B. permian's sequence differs from that of S. marismortui by only two features," they said.

Question of belief

"Are we to believe that in 250 million years B. permians has accumulated the same amount of genetic differences that could be achieved in just 3-7 days in the laboratory?" was the question they posed for the original researchers.

What is more, the pair also took a swipe at all other claims that ancient DNA has been obtained from a dinosaur bone, a Cretaceous weevil and a Miocene Magnolia plant. They believe they are all due to contamination by modern bacteria.

Needless to say, the original researchers want their right of reply.

"I disagree with them," Professor Vreeland told BBC News Online, "I don't argue that our claims should not be analysed by others, but I say that what we did cannot be disproved in this manner because we have no idea about how fast mutations occur in living microbes."

"There is some new evidence emerging that bacteria evolve faster in the lab than they do in the wild. It suggests that in some instances bacteria in the wild take centuries to change in a way that takes only days in the lab," he explained.

'Into the wild'

Vreeland's co-worker, Dennis Powers, said that Professor Graur and Dr Pupko have missed an entire set of arguments that "may well render their molecular clock arguments about the evolution of bacteria useless".

Powers believed that the 250 million-year-old-bacteria might have already escaped "into the wild".

He points out that part of the Salado formation, where the bacterium was obtained, is being dissolved, with the resulting briny water feeding into the Pecos River, and thence into the world's oceans via the Rio Grande.

This means that strain 2-9-3 might have already escaped from its ancient tomb and already be free in the environment.

Once free it would confuse the molecular clock method of tracing bacteria evolution.

Further work on B. Permians will be published shortly and no doubt the debate will continue.

But Vreeland is adamant: "Strain 2-9-3 is not a contaminant. I estimate that its chances of being a contaminant are less than one in a million."