[Vision2020] NASA: Discovery of "Arsenic-bug" Expands Definition of Life

[Ted Moffett]

http://science.nasa.gov/science-news/science-at-nasa/2010/02dec_monolake/

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.

"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 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.

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 at NASA
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Vision2020 Post: Ted Moffett