by Dwayne Brown (NASA Headquarters)
and Cathy Weselby (NASA Ames Research Center)
December 02, 2010
Image of Mono Lake Research area Image of Mono Lake Research area
Felisa Wolfe-Simon processing mud from Mono Lake to inoculate media
to grow microbes on arsenic Felisa Wolfe-Simon processing mud from
Mono Lake to inoculate media to grow microbes on arsenic.
Image Credit: Henry Bortman
GFAJ-1 grown on arsenic Image of GFAJ-1 grown on arsenic.
Image Credit: Jodi Switzer Blum
GFAJ-1 grown on phosphorus Image of GFAJ-1 grown on phosphorus.
Image Credit: Jodi Switzer Blum
NASA-funded astrobiology research has changed the fundamental
knowledge about what comprises all known life on Earth.
Researchers conducting tests in the harsh environment of Mono Lake
in California have discovered the first known microorganism on Earth
able to thrive and reproduce using the toxic chemical arsenic.
microorganism substitutes arsenic for phosphorus in its cell
"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
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.
metabolic pathways because chemically it behaves similarly to
"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.
here on Earth can do something so unexpected, what else can life do
that we haven't seen yet?"
The newly discovered microbe,
strain GFAJ-1, is a member of a common
group of bacteria, the
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
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
Arizona State University in Tempe, Ariz.
National Laboratory in Livermore, Calif.
Duquesne University in
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.