In a recent blog post, microbiologist Rosie Redfield is scathing concerning Felisa Wolfe-Simon’s recent claim, made in a scientific paper (Wolfe-Simon et al. 2010, A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus) that arsenic based life may have been discovered in Mono Lake in California:
NASA’s shameful analysis of the alleged bacteria in the Mars meteorite made me very suspicious of their microbiology, an attitude that’s only strengthened by my reading of this paper. Basically, it doesn’t present ANY convincing evidence that arsenic has been incorporated into DNA (or any other biological molecule). . . . If this data was presented by a PhD student at their committee meeting, I’d send them back to the bench to do more cleanup and controls.
Her blog post on this is long and full of data analysis such as the following:
The authors argue that the arsenate-grown cells don’t contain enough phosphorus to support life. They say that typical heterotrophic bacteria require 1-3% P to support life, but this isn’t true. These numbers are just the amounts found in E. coli cells grown in medium with abundant phosphate. They are very unlikely to apply to bacteria growing very slowly under phosphate limitation, and aren’t even true of their own phosphate-grown bacteria (0.5% P).
And her conclusion about the whole matter, as it now stands, is an affirmation of what it means to be a critical thinker and arrive at an issue with the determination to be objective, thorough, and skeptical:
There’s a difference between controls done to genuinely test your hypothesis and those done when you just want to show that your hypothesis is true. The authors have done some of the latter, but not the former. They should have mixed pregrown E. coli or other cells with the arsenate supplemented medium and then done the same purifications. They should have thoroughly washed their DNA preps (a column cleanup is ridiculously easy), and maybe incubated it with phosphate buffer to displace any associated arsenate before doing the elemental analysis. They should have mixed E. coli DNA with arsenate and then gel-purified it. They should have tested whether their arsenic-containing DNA could be used as a template by normal DNA polymerases. They should have noticed all the discrepancies in their data and done experiments to find the causes. I don’t know whether the authors are just bad scientists or whether they’re unscrupulously pushing NASA’s ‘There’s life in outer space!’ agenda. I hesitate to blame the reviewers, as their objections are likely to have been overruled by Science’s editors in their eagerness to score such a high-impact publication.
When you really want to know the truth about such a matter, Rosie Redfield spells out clearly what one ought to do. And these are great general rules of thumb as well, aren’t they?:
- Be objective.
- Be thorough.
- Be skeptical.
Would that the Ten Commandments had started this way. Rosie Redfield certainly deserves the high honor of being a member in good standing of the doubting community. I wonder if she’s also a skeptic of religious claims. Don’t you bet that she is?
It will be interesting to discover what Felisa Wolfe-Simon says to Rosie Redfield in response (if anything). This is getting interesting.