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Friday, December 3, 2010

Bacteria that grow on arsenic?

Update 1/23/12:  It looks like this study has now been completely refuted.  Rosie Redfield of the University of British Columbia made the following statement:
Their most striking claim was that arsenic had been incorporated into the backbone of DNA, and what we can say is that there is no arsenic in the DNA at all.

I probably will not post another update on this issue.  




Update 12/7/11:  It's now been a year since this paper was published, and no one has been able to replicate the results.  It doesn't look good for arsenic-based life forms.

Update:   Many other groups are calling into question whether this result is accurate. You can read some of their criticisms here.  Rosie Redfield, who wrote the cited article, is in the process of testing the arsenic hypothesis.  Thus far, her results are contradicting the following data.

Scientists have discovered claim to have discovered a type of bacteria growing in alkaline and salty Mono Lake, California that can incorporate arsenic into their cells. That claim has been called into question, as you can see by the update at the bottom of this post. These bacteria (a strain of Halomonadaceae called GFAJ-1) can use may use arsenic instead of phosphorus in various cellular structures, a hitherto assumed impossibility.


GFAJ-1

Until now, phosphorus was thought to be essential for all living things. Not only is it a key component of RNA, DNA and lipids, but it is also critical for energy storage and transport. Although phosphorus and arsenic are extremely similar elements, arsenic cannot replace phosporus in any other organisms without deadly result.

Somehow, GFAJ-1 is able may be able to use arsenic in place of phosphorus. When Felise Wolfe-Simon of Arizona State University and her colleagues grew the bacteria in increasing concentrations of arsenic and decreasing concentrations of phosphorus, the little critters were able to thrive. Using radioactive tracing, the researchers found that the microorganisms were actually incorporating arsenic rather than phosphorus into their DNA and cell membranes!

If true, this is an astounding discovery. Unfortunately, some people found the news anticlimactic, thanks to a statement by NASA saying they would be giving a press conference to "discuss an astrobiology finding that will impact the search for evidence of extraterrestrial life." People who thought they might be hearing that life had been found on one of Saturn’s moons were understandably disappointed to hear that life had been found in Mono Lake. That said, knowing that pools of arsenic don't preclude the possibility of life certainly widens the search parameters.

You can read more details and description at Bad Astronomy and at Not Exactly Rocket Science.