NASA-FUNDED RESEARCH DISCOVERS LIFE BUILT WITH TOXIC CHEMICAL
Dec. 02, 2010
fundamental knowledge about what comprises all known life on Earth. Researchers conducting tests in the harsh environment of
Lake 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. California
"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
. "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. Washington
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 , 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. Calif.
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
because of its unusual chemistry, especially its high salinity, high alkalinity,
and high levels of Mono Lake
arsenic. This chemistry is in part a result of
's isolation Mono
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
"Until now a life form using arsenic as a building block was only
theoretical, but now we know such life exists in Mono Lake." Moffett Field, Calif.
[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.]