To chemists, the discovery of a microbe that has incorporated arsenic into its DNA would be akin to finding that the formulation for water can shift from H2O -- two hydrogen atoms paired up with an oxygen -- to H3O.
Which is not to say that it couldn't happen, just that 100 years of organic chemistry says otherwise.
That doesn't really bother Felisa Wolfe-Simon, an oceanographer working under a NASA fellowships at the U.S. Geological Survey and the lead researcher of a paper to be published this week claiming evidence for just such a microorganism.
The paper's pre-publication in December led to such howls of protest that the esteemed Science magazine on Friday posted eight critical assessments of the research, along with Wolfe-Simon's response, on its website. All will be published in this week's magazine.
Wolfe-Simon's microbe, named GFAJ-1, was painstakingly weaned off its native phosphorous, one of the six building blocks of life, in favor of arsenic, which should have been fatal. The bacteria came from the salty sediments of Mono Lake in California.
If true, the finding presents the possibility that alternative life forms can exist, or once existed, on Earth. It also opens the floodgates for scientists developing techniques to find life beyond Earth and raises the prospect of alternative industrial uses of chemicals in fields ranging from manufacturing to medicine to energy.
"We were aware that what we were saying could be considered controversial," Wolfe-Simon told Discovery News. "We were very conservative in how we wrote the paper."
"For example, we never claimed that 100 percent of the phosphorous was substituted by arsenic," Wolfe-Simon said. "We're absolutely confident about the data we made and we argue in our technical response that we think the conclusions we draw are valid."
She acknowledges her critics raise valid points as well, including the possibility of contamination. The proof will come when the microbe's DNA are structurally analyzed, work that is still under way.
"That wasn't the goal of the first paper," Wolfe-Simon said. "The goal was to get this out into the community for people to think about."
In their response to critics, the researchers were not allowed to present any new evidence, but they did bulk up their arguments by citing four additional papers, one dating back to the 1960s, that buttress various branches of their findings.
Steve Benner, with the Foundation for Applied Molecular Evolution in Gainesville, Fla., generously describes the situation as a scientific culture clash.
"We're talking past each other," Benner told Discovery News.
Among Benner's problems with the research is that arsenic should fall apart in the presence of water. Wolfe-Simon's response that maybe the organism found a way to insulate its arsenic so that its chemical bonds are stronger begs the question of how that's possible, he said.
"They say, 'Well, it's conceivable ... now, back to you.' It's like watching two lawyers each trying to shift the burden of proof onto the other guy," Benner said.
The bottom line is we don't know why the cells grew when the arsenic was provided, added microbiologist Rosie Redfield, with the University of British Columbia, who also has challenged Wolfe-Simon's findings.
"I don't find their discussions about growth convincing at all in the absence of better data," she told Discovery News.
Wolfe-Simon's team is offering to send researchers cultures of the microbe for independent testing, an offer Redfield said she is considering.
As for Wolfe-Simon, she is continuing her own research on the microbes and has added four new scientists to her team to address DNA analysis and other issues.
"Everyone seems to have their own 'silver bullet' analysis," she said. "While our work isn't definitive, it does suggest that biology can be a whole lot more flexible than we normally attribute to it. If we find microbial life, here or elsewhere, doing something even a little different, that could be profound."