-- Visions of aliens danced in a lot of heads last December, when NASA held a press conference, promising an "astrobiology finding that will impact the search for evidence of extraterrestrial life."
What scientists disclosed was the discovery of a bacteria, pulled from California's Mono Lake, that added deadly arsenic to the list of six basic elements believed needed for life — carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus. The idea that a microbe could bring poisonous arsenic into its DNA and thrive threw the conventions of biology on its head.
NASA was interested because even skeptical scientists such as Steven Benner of the Foundation for Applied Molecular Evolution, (who served as the token critic on the space agency panel presenting the results) pointed out that if life on Earth could thrive on something as nasty as arsenic, the opportunities for life on other worlds seemed much more expansive. .
"Arsenic had completely replaced phosphate in the molecules of the bacteria, right down (to) its DNA," Science magazine's news release said, touting the study reporting the bacteria. The announcement was greeted seemingly with equal amounts of media acclaim and derision from outside scientists. University of British Columbia microbiologist Rosie Redfield, for example, called it "shamefully bad science," finding the evidence for the bacteria substituting poisonous arsenic for phosphates unconvincing.
Now, as we reach the first anniversary of the "arseniclife" bacteria debate, a research team is throwing more cold water on the original finding. In results just posted to the National Center for Biotechnology Information's website, the team led by Le Phung of the University of Illinois in Chicago, has produced the genetic map, or genome, of this remarkable bacteria (also known as GFAJ-1), one that the team says doesn't look all that remarkable.
"There's no arsenic in its DNA. Its genes don't even look particularly arsenic-resistant," says genome team scientist Simon Silver, also of the University of Illinois, a pioneer in the field of arsenic-resistant microbes. The results show a saltwater bacteria with 3,409 genes. None of them look like identified arsenic resistance genes found in other bugs, he says. "It's incredibly like a typical E. coli bacteria, only with a smaller genome," Silver says.
Silver has been a leading critic of the original "arseniclife" study (which he labels "garbage"), over the last year, calling it "magic and nonsense" in a commentary published in the journal, FEMSMicrobiology Letters. Phung and colleagues plan to submit the new genome report to the Journal of Bacteriology, for review by other scientists.
"This doesn't say anything about whether we are right or wrong, it's just another step in the process of science," says "arseniclife" study senior author Ron Oremland of the U.S. Geological Survey in Menlo Park, Calif. A genome by itself doesn't mean anything, he says, unless evaluated along with reports by other scientists of the basic biology of the bug. "The genome by itself is just a tool to help other researchers. We didn't expect it to look extraordinary."
Oremland says his lab is no longer running GFAJ-1 bug experiments, only making the bacteria available to other researchers to test. "We're all pretty exhausted by this," he says. "Besides no one will believe my lab's results at this point. We need other groups to release their independent findings."
Although skeptical of the "arseniclife" paper, Benner is also cautious about the genome results. If the bugs were truly grown in an arsenic-rich environment mirroring the one in the original Science paper, he says, then the results would have more credence. And the type of genetic sequencing done may also affect the result, because modern gene-sorting machines aren't designed to handle DNA containing arsenic in the first place.
"Just because it doesn't seem to have any known arsenic (resistance) genes doesn't mean there aren't other unrecognized ones in the genome," Benner adds. Still, purely from a chemical basis, he says arsenic looks "far too unstable" to play nice with the other chemicals in DNA.
Despite the contention, Oremland and his colleagues did help Phung's genome team grow the bugs for the experiment. After all, Silver and Oremland have wagered a bottle of Scotch on the ultimate outcome of the "arseniclife" debate. "He (Silver) owes me a bottle of Scotch already, just for putting up with him," Oremland says, jokingly. "Luckily he doesn't drink that much now, so whatever way the bet goes, I'll help him polish it off."