Discovery of "Arsenic-bug" Expands Definition of Life   
       
   Dec. 2, 2010:  NASA-supported researchers have discovered the first known   
   microorganism on Earth able to thrive and reproduce using the toxic chemical   
   arsenic. The microorganism, which lives in California's Mono Lake, substitutes   
   arsenic for phosphorus in the backbone of its DNA and other cellular   
   components.   
   [...]   
   A microscopic image of GFAJ-1 grown on arsenic. [larger image] "The definition   
   of life has just expanded," said Ed Weiler, NASA's associate administrator for   
   the Science Mission Directorate at the agency's Headquarters in Washington.   
   "As we pursue our efforts to seek signs of life in the solar system, we have   
   to think more broadly, more diversely and consider life as we do not know it."   
       
   This finding of an alternative biochemistry makeup will alter biology   
   textbooks and expand the scope of the search for life beyond Earth. The   
   research is published in this week's edition of Science Express.   
       
   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.   
       
   "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?"   
   [...]   
   The Mono Lake Research area in central California. [larger image]  [more]   
       
   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.   
   [...]   
   Geomicrobiologist Felisa Wolfe-Simon, collecting lake-bottom sediments in the   
   shallow waters of Mono Lake in California. Credit: c2010 Henry Bortman [more]   
       
   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.   
       
   NASA's Astrobiology Program in Washington contributed funding for the research   
   through its Exobiology and Evolutionary Biology program and the NASA   
   Astrobiology Institute. NASA's Astrobiology Program supports research into the   
   origin, evolution, distribution, and future of life on Earth.   
       
       
   Editor: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   NASA Astrobiology -- home page   
       
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