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December
2, 2010-- From toxicity
to life: arsenic proves to be a building block
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Oxygen,
carbon, hydrogen, nitrogen, sulfur and phosphorous are the
six basic building blocks of life on Earth. These elements
make up nucleic acids, proteins and lipids - the bulk of
living matter.
Arsenic
- an element that triggers death for most Earthly life forms
- is actually allowing for a bacterium to thrive and reproduce.
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In
a study that may prompt the rewriting of textbooks, a team of
astrobiologists and chemists has found the first known living
organism that can use arsenic in place of phosphorus in its major
macromolecules. The new findings, published in the Dec. 2 Science
Express, could redefine origins of life research and alter the
way we describe life as we know it.
LLNL's
Jennifer Pett-Ridge and Peter Weber were able to identify low
concentrations of arsenic found in individual cells of bacteria
and extracted DNA. NanoSIMS is a tool which allows precise, spatially
explicit, elemental and isotopic analysis down to the 50-nanomenter
scale; it also offers a range of advantages for sensitive and
high-resolution measurements.
"It
turned out the organism was able to tolerate these heavy metal
concentrations (that are found in Mono Lake)," Pett-Ridge said.
"Arsenic is right below phosphorous on the periodic table and
it may have found a way to substitute arsenic for phosphorous
in its biological makeup."
Cultures
of the Mono Lake samples produced flourishing colonies of the
bacterium cells, as expected, when fed a steady supply of phosphorus,
along with other necessities. When researchers removed the phosphorus
and replaced it with arsenic, however, the microbes continued
to grow. Subsequent analyses indicated that the arsenic was being
used to produce the building blocks of new cells.
"The
team hasn't yet established how the organism uses arsenic as a
building block when it's a poison to most other life forms," Pett-Ridge
said. "It could be an ancestral trait or a unique kind of metabolism.
Or it could be that it lives in an environment where arsenic is
very high and it found a niche to survive."
"This
organisms' metabolic lifestyle suggests that life based on non-typical
elements may be possible," Wolfe-Simon said. "This is important
to scientists looking for clues to life on other planets."
NanoSIMS
not only measures the elemental concentrations, but it also images
them. It collects a picture of the image and identifies how much
of a specific element is found in the sample. "We found that arsenic
was higher in the cells than in the environment outside the cells,"
Pett-Ridge said.
"It's
very difficult to make these measurements because the sample concentrations
of arsenic are very low," she said. "But it's clear that the cells
are incorporating arsenic into them. There are not a lot of organisms
on the planet that can do this. " The next step is to conduct
protein biochemistry to find out if there are specific enzymes
that help transport arsenic into the cells. Other collaborators
include NASA Astrobiology Institute, Arizona State University,
Duquesne University, Stanford Synchrotron Radiation Lightsource
and BEYOND: Center for Fundamental Concepts in Science at Arizona
State University.
The
next step is to conduct protein biochemistry to find out if there
are specific enzymes that help transport arsenic into the cells.
Other collaborators include NASA Astrobiology Institute, Arizona
State University, Duquesne University, Stanford Synchrotron Radiation
Lightsource and BEYOND: Center for Fundamental Concepts in Science
at Arizona State University.
Source:
DOE/Lawrence Livermore National Laboratory
Anne M Stark, LLNL, (925) 422-9799, stark8@llnl.gov
A
Bacterium That Can Grow by Using Arsenic Instead of Phosphorus
-Felisa Wolfe-Simon1,2,*, Jodi Switzer Blum2, Thomas R. Kulp2,
Gwyneth W. Gordon3, Shelley E. Hoeft2, Jennifer Pett-Ridge4, John
F. Stolz5, Samuel M. Webb6, Peter K. Weber4, Paul C. W. Davies1,7,
Ariel D. Anbar1,3,8 and Ronald S. Oremland2
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