Henry Bortman / 2010
Astrobiology researcher Felisa Wolfe-Simon works with samples at California's Mono Lake.
The controversy over findings that suggest life can grow using arsenic entered a new phase today: The researchers behind the radical claim issued a statement responding to their critics — and said the comments and responses generated by their experiments would be reviewed and published in a future issue of the journal Science.
In their original study, published online by the journal Science on Dec. 2, the researchers suggested that salt-loving bacteria gathered from California's Mono Lake could be coaxed to substitute atoms of arsenic, which is toxic to life on Earth, in place of the usual phosphorus atoms in DNA and other parts of their cellular machinery.
Since that study was published, a number of microbiologists and chemists have questioned whether the experiments actually proved the researchers' point. The critics said inadequate care was taken in purifying DNA samples from the bacteria in the arsenic-rich medium, and that the arsenic found in the DNA was merely contamination. They said that the bacteria might have been using trace amounts of phosphorus left as impurities in the growth medium, and that arsenic bonds in the DNA could not have stood up to exposure to water.
For the past couple of weeks, members of the Mono Lake research team have declined to respond in detail to the criticisms, saying that they preferred to address questions through a peer-reviewed process. But today, team leaders Felisa Wolfe-Simon and Ron Oremland of the U.S. Geological Survey said they were providing additional information about the experiments "as a public service ... while more formal review of their responses to comments sent to Science continues."
In a preliminary Q&A, Wolfe-Simon and Oremland recapped the procedures they went through to purify arsenic-laden DNA and said they felt the critics' concerns about the procedures were not valid. They also said "it is conceivable" that DNA containing arsenic is more resilient to water exposure than previously thought, although they acknowledged that "more research is warranted" on this question.
They pointed out that the Mono Lake bacteria could not grow unless either arsenic or phosphorus was added to the medium. Such data "clearly demonstrate" that the trace amounts of phosphorus left in the medium were insufficient to support further growth, they said.
In their conclusion, the research team reflected on what they've gone through and what lies ahead:
"For all of us, our entire team, what this was like was unimaginable. We are a group of scientists that came together to tackle a really interesting problem. We each used our talents, from technical prowess to intellectual discussion, to objectively determine what exactly was happening in our experiments. We freely admitted in the paper and in the press that there was much, much more work to do by us and a whole host of other scientists. The press conference even included a technical expert, Dr. Steven Benner, who voiced some of the concerns we responded to above. Part of our reason for bringing this work to the community was to make the intellectual and technical connections for more collaborations to answer many of the lingering questions. We were transparent with our data and showed every datum and interesting result. Our paper’s conclusions are based on what we felt was the most parsimonious way to interpret a series of experiments where no single experiment would be able to answer the big question. 'Could a microbe use arsenic in place of phosphorus to sustain its growth?' The best science opens up new questions for us as a community and sparks the interest and imagination of the general public. As communicators and representative of science, we feel that support of new ideas with data is critical but also to generate new ideas for others to think about and bring their talents to bear on.
"We look forward to working with other scientists, either directly or by making the cells freely available and providing DNA samples to appropriate experts for their analyses, in an effort to provide more insight into this intriguing finding."
Science is making the original study as well as its news article about the research available for free online with registration. If you're interested in this issue, be sure to read today's full statement — and feel free to comment below.
Update for 11:55 p.m. ET: Rosie Redfield, a microbiologist at the University of British Columbia who was a prominent critic of the original "arsenic life" research, has posted her critique of the today's statement.