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    GFAJ-1: Has This Microbe Redefined The Definition Of Life?
    By News Staff | December 2nd 2010 04:50 PM | 6 comments | Print | E-mail | Track Comments
    Astrobiology researchers say a new discovery may have expanded the definition of life.   Conducting tests in the harsh environment of Mono Lake in California, they have discovered the first known microorganism on Earth able to thrive and reproduce using the toxic chemical arsenic, substituting arsenic for phosphorus in its cell components. 

    Carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur are the six basic building blocks of all known forms of life on Earth. Phosphorus is part of the chemical backbone of DNA and RNA, the structures that carry genetic instructions for life, and is considered an essential element for all living cells.

    Phosphorus is a central component of the energy-carrying molecule in all cells (adenosine triphosphate) and also the phospholipids that form all cell membranes. Arsenic, which is chemically similar to phosphorus, is poisonous for most life on Earth. Arsenic disrupts metabolic pathways because chemically it behaves similarly to phosphate.

    This finding of an alternative biochemistry makeup could alter biology textbooks and expand the scope of the search for life beyond Earth, they write in Science Express.

    "We know that some microbes can breathe arsenic, but what we've found is a microbe doing something new -- building parts of itself out of arsenic," said Felisa Wolfe-Simon, a NASA Astrobiology Research Fellow in residence at the U.S. Geological Survey in Menlo Park, Calif., and the research team's lead scientist. "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?"

    GFAJ-1 grown on phosphorus
    Image of GFAJ-1 grown on phosphorus.

    GFAJ-1 grown on arsenic
    Image of GFAJ-1 grown on arsenic.

    The newly discovered microbe, strain GFAJ-1, is a member of a common group of bacteria, the Gammaproteobacteria. In the laboratory, the researchers successfully grew microbes from the lake on a diet that was very lean on phosphorus, but included generous helpings of arsenic. When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells.

    The key issue the researchers investigated was when the microbe was grown on arsenic did the arsenic actually became incorporated into the organisms' vital biochemical machinery, such as DNA, proteins and the cell membranes. A variety of sophisticated laboratory techniques was used to determine where the arsenic was incorporated.

    The team chose to explore Mono Lake because of its unusual chemistry, especially its high salinity, high alkalinity, and high levels of arsenic. This chemistry is in part a result of Mono Lake's isolation from its sources of fresh water for 50 years.





    The results of this study will inform ongoing research in many areas, including the study of Earth's evolution, organic chemistry, biogeochemical cycles, disease mitigation and Earth system research. These findings also will open up new frontiers in microbiology and other areas of research.

    "The idea of alternative biochemistries for life is common in science fiction," said Carl Pilcher, director of the NASA Astrobiology Institute at the agency's Ames Research Center in Moffett Field, Calif. "Until now a life form using arsenic as a building block was only theoretical, but now we know such life exists in Mono Lake."

    The research team included scientists from the U.S. Geological Survey, Arizona State University in Tempe, Ariz., Lawrence Livermore National Laboratory in Livermore, Calif., Duquesne University in Pittsburgh, Penn., and the Stanford Synchroton Radiation Lightsource in Menlo Park, Calif.

    Citation: Felisa Wolfe-Simon, Jodi Switzer Blum, Thomas R. Kulp, Gwyneth W. Gordon, Shelley E. Hoeft, Jennifer Pett-Ridge, John F. Stolz, Samuel M. Webb, Peter K. Weber, Paul C. W. Davies, Ariel D. Anbar, and Ronald S. Oremland, 'A Bacterium That Can Grow by Using Arsenic Instead of Phosphorus', Published online 2 December 2010 DOI:10.1126/science.1197258

    Comments

    Gerhard Adam
    When researchers removed the phosphorus and replaced it with arsenic the microbes continued to grow. Subsequent analyses indicated that the arsenic was being used to produce the building blocks of new GFAJ-1 cells.
    So, it would appear that this isn't a life-form that uses arsenic in its biochemistry, although it is a microorganism that CAN use arsenic in its biochemistry.  I understand that these microorganisms have been living in this environment for some period of months, so it isn't just a temporary adaptation, but I'm wondering if this is an anomaly because I don't believe arsenic is stable enough for use in DNA unless there is another binding mechanism at work.
    Mundus vult decipi
    Aitch
    Original article

    http://www.nasa.gov/topics/universe/features/astrobiology_toxic_chemical...

    Though not the only interesting life form at Mono Lake, see for example, the Alkali fly

    http://www.monolake.org/about/ecoflies

    Far more likely to have evolved due to the conditions at Mono Lake, than be an alien lifeform, though...

    http://news.yahoo.com/s/space/20101202/sc_space/arseniceatingbacteriaope...

    Unless you're short of news, and like scaring people unnecessarily...

    LA may want to look at its water use.....

    Support the restoration project: https://secure2.convio.net/mlc/site/Donation2?df_id=1520&1520.donation=f...

    Watch the film




    Aitch
    Hank
    According to a new paper published in Science, reporters are unable to thrive in an arsenic-rich environment

    As Leonid Kruglyak put it, "According to a new paper published in Science, reporters are unable to thrive in an arsenic-rich environment."  XKCD makes it funnier with stick people.
    I didn't think the definition of life included carbon based and environmental factors

    just - some form of respiration, absorption/excretion, reproduction and some amount of movement.

    I think the mimivirus was more of a game changer
    http://www.microbiologybytes.com/virology/Mimivirus.html

    I have a really hard time believing this conclusion - especially the assertion that arsenic use by this microbe is facultative (optional) rather than obligatory.
    How can a cell handle DNA that is partially made with phosphorus and partially with arsenic? In DNA replication, for example, the two strands separate and each gets a new partner. Now you have what - a phosphorus strand joined with an arsenic strand? There are so many steps where these molecules must be manipulated. The microbe would require duplicate machinery to handle both varieties side by side.
    And phosphorus appears in many places besides DNA - in RNA, for example. And in membranes - can you really build a membrane partially out of phosphorus and partially out of arsenic? The ubiquitous energy source ATP - is it replaced by adenosine triarsenate? And can the cell do its metabolizing using either?
    If the cell is in fact incorporating arsenic, it seems much more likely to me that it is doing so as a defensive measure, perhaps being sequestered in the vacuoles that they've observed. This work really needs a lot of independent confirmation.

    Steve Davis
    "If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?" There they go again! Making the issue more complex than it really is. They have no firm basis for a definition of life, but are happy to muddy the waters with speculation like that. Can I suggest that they read my article "What is Life?" where they will find a definition that fits the data.