NASA-FUNDED RESEARCH
DISCOVERS LIFE BUILT WITH TOXIC CHEMICAL
From NASA
Dec. 02, 2010
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. The microorganism substitutes
arsenic for phosphorus in its cell 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 were 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."
[Of course the idea of
alternative biochemistries means that the scope for life increases appreciably.
We no longer have to assume that for life to exist on other worlds that those
worlds must be as close as possible to our world in their basic make-up. That
being the case the possibility of life in what we would consider unsuitable or
extreme environments must increase and with it the possibility – or indeed
probability – of life being even more widespread than previously thought.]
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