From Nature magazine

After 18 months of controversy, the official verdict is in: an arsenic-tolerant bacterium found in California’s Mono Lake cannot live without phosphorus.

In 2010, a group led by Felisa Wolfe-Simon, a microbiologist now at the Lawrence Berkeley National Laboratory in Berkeley, California, reported online in Science¹ that the Halomonadaceae bacterium GFAJ-1 could include atoms of arsenic instead of phosphorus in crucial biochemicals such as DNA.

The bacteria were discovered thriving in the arsenic-rich sediment of the shallow saline Mono Lake, famed for its appearance on a picture-postcard insert to Pink Floyd’s 1975 album Wish You Were Here.

All known forms of life depend on at least six elements: hydrogen, carbon, nitrogen, oxygen, phosphorus and sulphur. Arsenic has some chemical similarities with phosphorus, but is usually toxic to life, so the suggestion that it could sustain life triggered a storm of questions, as well as criticism about how the find was revealed at an enthusiastic NASA press conference (see ‘Microbe gets toxic response’).

As a result of the controversy, when Wolfe-Simon's paper appeared in print in Science last June, it was accompanied by eight technical comments^2–9 from scientists responding to it.

Rosie Redfield, a microbiologist at the University of British Columbia in Vancouver, Canada, set about testing the finding. Earlier this year, she said that she could not reproduce Wolfe-Simon’s results in laboratory experiments (see ‘Study challenges existence of arsenic-based life’).

Redfield is now a co-author of one of two papers that confirm that, although the bacteria can tolerate arsenic, they do depend on phosphorus. The papers were published^{10, 11} by Science on 8 July.

Toxicity tolerance
Redfield and her colleagues report¹⁰ that when GFAJ-1 bacteria were grown in a medium containing arsenic and a very small amount of phosphorus, their DNA contained no detectable arsenic compounds, such as arsenate (the arsenic analogue of phosphate). In the second paper, Julia Vorholt, a microbiologist at the Federal Institute of Technology in Zurich, Switzerland, and her colleagues report¹¹ that the bacterium cannot grow in a phosphorus-free medium in the presence of arsenate. It can, however, grow in low-phosphate conditions in the presence of arsenate. GFAJ-1 “is an arsenate-resistant, but still a phosphate-dependent bacterium”, the team writes.

3 Comments

1. 1. Zexks 02:52 PM 7/9/12

   And this is why if you want anyone to take what you're saying seriously it needs to be published in a peer reviewed journal so others can either verify or invalidate your findings. That is the beauty of science.

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2. 2. RJChurchill 11:42 AM 7/11/12

   I am somewhat surprised that the article got as far as it did. Mass spectroscopy would have been one of the most elementary tools to use in order to prove the assertion that arsenic could be a substitute for phosphorous in terrestrial life in this particular case.

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3. 3. Carlyle in reply to Zexks 09:19 AM 7/14/12

   Yes. Genuine peer review, not all members of the same sewing circle.

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