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Arsenic biochemistry

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Arseno-DNA refers to a hypothetical DNA analog in which arsenate partially or fully replaces phosphate present in its backbone. This analog has been proposed to be sustainable in vivo in GFAJ-1 bacteria.

Discovery

Further information: GFAJ-1

A 2010 paper in Science[1] reports that GFAJ-1 is facultatively capable of incorporating arsenate into its DNA under conditions of phosphorus starvation. NASA announced at a press conference on 2 December 2010 the discovery of an organism that has been proposed to utilize arsenic in its cellular structure. The organism was dubbed GFAJ-1 by the team leader, Felisa Wolfe-Simon; GFAJ stands for "Give Felisa a Job."[2] During the press conference, the implications to astrobiology were emphasized. If this proposal is verified, it would constitute the first discovery of a life form capable of replacing one of the primary six chemical elements in its makeup, namely: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur (or "CHNOPS" for short).[3][4][5][6][7][8]

Arsenic, which is chemically similar to phosphorus, while poisonous for most life forms on Earth, is incorporated into the biochemistry of some organisms.[9] Some marine algae incorporate arsenic into complex organic molecules such as arsenosugars and arsenobetaines. Fungi and bacteria can produce volatile methylated arsenic compounds. Arsenate reduction and arsenite oxidation have been observed in microbes such as Chrysiogenes arsenatis.[10] Additionally, some prokaryotes can use arsenate as a terminal electron acceptor during anaerobic growth and some can utilize arsenite as an electron donor to generate energy. In the context of astrobiology, it has been speculated that the earliest life forms on Earth may have used arsenic in place of phosphorus in the backbone of their DNA.[11][12][13]

Criticism

At the NASA press conference (2 December 2010) announcing Wolfe-Simon's results, chemist Steven A. Benner expressed some skepticism that arsenate was substituted for phosphate in the DNA backbone of these organisms unless other new mechanisms were present in the organism to prevent hydrolysis of the arsenate ester chemical bonds.[14] If the proposal that bacterium GFAJ-1 uses arsenate in its DNA and other biomolecules is correct, then the bacterium must have a way of stabilizing arsenate esters or otherwise working around this limitation. Wolfe-Simon speculates that this stability might be accomplished in part by isolating some arsenate-containing molecules in large vacuole compartments rich in poly-β-hydroxybutyrate that GFAJ-1 develops when cultured in arsenic but not when cultured in phosphorus.[1] Others have pointed out that the method used to isolate the DNA requires that it be isolated in an aqueous environment for over an hour where no natural stabilizing mechanism would be available. Benner even went so far as to wager Wolfe-Simon $100 that she had not observed arseno-DNA.[15]

Other scientists are also skeptical with the announced results;[14] microbiologists Rosemary Redfield[16] and, separately, Athena Andreadis[17] have suggested the claims could potentially be based on errors in how the research studies were conducted. Several chemists, including Nicholas Winograd, Keith Hodgson, Gerald Joyce, Ronald S. Oremland and John D. Sutherland, have suggested that the the science was incomplete and/or flawed and that the NASA press release was premature. Other expressed dismay at how the videocast was officially pre-announced as a NASA announces breakthrough and “An astrobiological finding that will impact the search for evidence of extraterrestrial life.” Some compared the gaps in peer review and the style of the press release with the embarrassment that NASA astrobiology suffered with Allan Hills 84001 speculation about life on Mars or the "science by press release" associated with cold fusion.[18][19][20] [21][22][23][24][25][26][27][28][29]

Simon-Wolfe responded in part by posting on her website a copy of a mildly-critical article that was published in the same issue as her paper,[30] and by promising an online FAQ in the near future. She has also suggested that while she allowed herself an hour-long NASA videocast with much speculation about astrobiology and references to and near-impersonations of Carl Sagan, she will refuse to address any criticism about her work or about the subject other than that appearing in traditional peer-reviewed journals.

See also

References

  1. ^ a b Wolfe-Simon, Felisa; Blum, Jodi Switzer; Kulp, Thomas R.; Gordon, Shelley E.; Hoeft; Pett-Ridge, Jennifer; Stolz, John F.; Webb, Samuel M.; Weber, Peter K.; Davis, Paul C. W.; Anbar, Ariel D.; Oremland, Ronald S. (2 December 2010). "A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus" (PDF). Science. doi:10.1126/science.1197258. PMID 21127214. Retrieved 2010-12-09. {{cite journal}}: Missing |author12= (help)
  2. ^ Davies, Paul (4 December 2010). "The 'Give Me a Job' Microbe". Wall Street Journal. Retrieved 2010-12-09.
  3. ^ Palmer, Jason (2 December 2010). "Arsenic-loving bacteria may help in hunt for alien life". BBC News. Retrieved 2010-12-02.
  4. ^ Kottke, Jason (29 November 2010). "NASA news conference participants". Kottke.org. Retrieved 2010-12-02.
  5. ^ Katsnelson, Alla (2 December 2010). "Arsenic-eating microbe may redefine chemistry of life". Nature News. doi:10.1038/news.2010.645. Retrieved 2010-12-02.
  6. ^ NASA - Astrobiology Magazine: "Searching for Alien Life, on Earth" October 2009
  7. ^ Bortman, Henry (5 October 2009). "Searching for Alien Life, on Earth". Astrobiology Magazine (NASA). Retrieved 2010-12-02.
  8. ^ Harvey, Mike (4 March 2010). "Could the Mono Lake arsenic prove there is a shadow biosphere?". UK: The Times. Retrieved 2010-12-02.
  9. ^ "Biochemical Periodic Table - Arsenic". Umbbd.msi.umn.edu. 2007-06-08. Retrieved 2010-05-29.
  10. ^ Niggemyer, A (2001). "Isolation and characterization of a novel As(V)-reducing bacterium: implications for arsenic mobilization and the genus Desulfitobacterium". Appl Environ Microbiol. 67 (12): 5568–80. doi:10.1128/AEM.67.12.5568-5580.2001. PMC 93345. PMID 11722908. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help)
  11. ^ Reilly, Michael (26 April 2008). "Early life could have relied on 'arsenic DNA'". New Scientist. 198 (2653): 10. doi:10.1016/S0262-4079(08)61007-6.
  12. ^ "NASA-Funded Research Discovers Life Built With Toxic Chemical". NASA.gov. 2 December 2010. Retrieved 2010-12-02.
  13. ^ Dennis Overbye (December 2, 2010). "Thriving on Arsenic, a Microbe May Redefine Life". New York Times.
  14. ^ a b Bortman, Henry (2010-12-02). "Arsenic-Eating Bacteria Opens New Possibilities for Alien Life". Space.Com web site. Retrieved 2010-12-02. {{cite web}}: External link in |work= (help) Alt URL Cite error: The named reference "Bortman" was defined multiple times with different content (see the help page).
  15. ^ 'Weird life' claims spark a backlash Alan Boyle, MSNBC Cosmic Log, 2010-12-07
  16. ^ Redfield, Rosemary J. (4 December 2010). "Arsenic-associated bacteria (NASA's claims)". RR Research blog. Retrieved 2010-12-06. {{cite web}}: External link in |work= (help)
  17. ^ Andreadis, Athena (3 December 2010). "Arsenic and Odd Lace". The Huffington Post. The Huffington Post. Retrieved 2010-12-08. {{cite web}}: External link in |work= (help)
  18. ^ Arsenic Bacteria Breed Backlash: Controversy: Claim that microbe weaves arsenic into its DNA comes under fire December 8, 2010
  19. ^ "This Paper Should Not Have Been Published": Scientists see fatal flaws in the NASA study of arsenic-based life. by Carl Zimmer, Slate.com, Dec. 7, 2010
  20. ^ Scientists poke holes in NASA’s arsenic-eating microbe discovery by Brett Michael Dykes, The Outlook (a Y! news blog), Dec. 8 2010
  21. ^ But can it grow? The Triplicate, December 9, 2010
  22. ^ An arsenic bacteria postmortem: NASA responds, tries to pit blogs vs. “credible media organizations” Embargo Watch, 2010-12-07
  23. ^ Death for "Arsenic-Based Life"? : A hotly anticipated announcement last week from nasa that scientists had discovered an exotic form of life ended up revealing more about science journalism Dave Munger, 2010-12-07
  24. ^ Debate Over Discovery of Arsenic-Based Life Gets Lively by Mike Wall, 07 December 2010
  25. ^ Doubts Brew About NASA’s New Arsenic Life by Lisa Grossman, December 7, 2010
  26. ^ Microbe gets toxic response: Researchers question the science behind last week's revelation of arsenic-based life Alla Katsnelson, Nature, Nature 468, 741 (2010), 2010-12-07 doi:10.1038/468741a
  27. ^ NASA's arsenic microbe science slammed December 6, 2010
  28. ^ Hey, NASA: this is what peer review actually looks like by Chris Rowan, December 7, 2010
  29. ^ The Right Place for Scientific Debate? : Scientists snub media as controversy over arsenic-eating microbes rolls on by Curtis Brainard, The Observatory, December 7, 2010
  30. ^ What Poison? Bacterium Uses Arsenic to Build DNA and Other Molecules by Elizabeth Pennisi, Science Magazine, Vol. 330 no. 6009 p. 1302, doi:10.1126/science.330.6009.1302, 3 December 2010
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