[meteorite-list] DNA Analysis May Be Done On Mars For First Time

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 9 Apr 2009 15:28:46 -0700 (PDT)
Message-ID: <200904092228.PAA28977_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/article/dn16933-first-dna-analysis-may-be-done-on-another-planet.html

DNA analysis may be done on Mars for first time
by Ewen Callaway
New Scientist
09 April 2009

In August 1996, molecular biologist Gary Ruvkun was about to reveal
one of the biggest discoveries of his scientific career. His lab at
Harvard Medical School had recently found a gene called age-1 that
determines lifespan in roundworms. Their work offered the tantalising
possibility that tinkering with molecular pathways might extend the
lifespan of other organisms - and perhaps even humans.

Harvard sent out a press release and Ruvkun prepared for an onslaught of
media attention. But it never came. Two days before his team's paper
came out, scientists analysing a meteorite from Mars called ALH84001
made headlines worldwide. Then-US president Bill Clinton even got in on the
announcement <http://researchmagazine.uga.edu/summer2001/mars.html>.

"My grad student leans in the door and says, 'They've just announced
life on Mars,'" recalls Ruvkun. "That would really f--- us," Ruvkun
replied, thinking his student was joking.

Scientists have since raised serious doubts about the
existence of the purported fossilised microbes in the meteorite (see
image
<http://www.newscientist.com/articleimages/dn16933/1-first-dna-analysis-may-be-done-on-another-planet.html>).

But now, more than a decade after his work was overshadowed by news of
possible life on Mars, Ruvkun has joined the hunt to find it. Moreover,
he and his colleagues want to sequence its DNA.

Toehold for life

Today, Mars is a frozen, barren world. Ultraviolet light and energetic
space particles stream in through its thin atmosphere, sterilising any
life - at least as we know it - on its bone-dry surface.

But recent research suggests life might find a niche just below the
surface, where liquid water could be widespread. The discovery of
plumes of methane in the planet's atmosphere also hints at subsurface
life, since some terrestrial microbes produce the gas.

Chemical signs of life can be ambiguous,
but Ruvkun and his team hope to find its unequivocal signature by
sending a DNA amplifier and sequencer to Mars in the next decade.
They're betting that any life on the Red Planet shares an evolutionary
heritage with life on Earth, and therefore contains a similar genetic
code - a requirement that other scientists say is too narrowly focused,
since Martian life may have evolved independently and therefore may have
very different chemistry.

"This is a pure jackpot scheme. You either discover the most important
thing for a long time, or you discover nothing," says Ruvkun, who in
2008 won the Lasker Award <http://www.laskerfoundation.org/>, an honour
shared by 75 scientists who later went on to nab a Nobel.

Interplanetary travel

Why would Martian life be similar to that on Earth? About 4 billion
years ago, when terrestrial life probably got its start, rocky bodies
were flying through the solar system
and slamming into the planets. These impacts threw pieces of the planets
into space, and some of these pieces landed on other planets as meteorites.

Ancient microbes might have hitched a ride to or from Mars on these
meteorites. While in space, the surfaces of these rocks would have been
sterilised by UV radiation and then singed to a crisp entering the
atmosphere. But a large enough rock could support life beneath its
surface, Ruvkun says.

And life originating or landing on Mars some 4 billion years ago may
well have found the environment there hospitable. The planet may have
boasted a thicker atmosphere and liquid water on its surface, possibly
in the form of oceans.

"Mars was probably fit for life," says Paul Davies,
a cosmologist and astrobiologist at Arizona
State University in Tempe, who is not involved in the sequencing project.

Early prototype

NASA has bought into the possibility that life may have once travelled
between the two planets and is supporting early development of the
sequencing project, called the Search for Extraterrestrial Genomes (SETG
<http://web.mit.edu/setg/>).

The agency has already provided just under $2 million in funding for the
project, says Christopher Carr, an engineer in Ruvkun's lab who is
spearheading development of the device.

The latest prototype rests on a metal breadboard at one end of Carr's
lab bench, connected to a series of hydraulic pumps, electric wires and
cables. A more svelte, compact version of the instrument may one day
travel to Mars, perhaps on a mission planned for launch in 2018.
      
DNA glow

How would such an instrument work? Carr divides the project into four
distinct stages.

The first is preparing a sample from soil or ice that a future Mars
lander gathers from burrowing into the planet's surface.

After this sample is reconstituted in liquid and mixed with a dye that
fluoresces when it binds onto DNA, the device will funnel the sample
through a glass microfluidic chip filled with hundreds of tiny channels.
If one channel glows positive for DNA, its contents will move on to the
next stage - amplification.

It's no understatement to say that polymerase chain reaction (PCR)
revolutionised the practice of biology when it was invented in the
1980s. The technology allows researchers to create billions of identical
copies of a short stretch of DNA, simply by knowing the genetic sequence
of its two ends.

It's also astonishingly sensitive and simple, requiring little more than
a single 'template' DNA molecule, a heat source and some raw chemical
materials. "PCR is done in junior high school," Ruvkun told New
Scientist. "That's the definition of what you want to send to Mars."

Sequencing technologies

To determine whether DNA on Mars shares ancestry with terrestrial life,
his team will amplify a gene called the 16S ribosomal RNA subunit. It
encodes an RNA molecule that's part of the ribosome, a cell's crucial
protein factory.

Ruvkun's team isn't yet sure how they'll decode the amplified DNA. The
same sequencing technologies that might deliver a $1000 complete human
genome sequence in the next few years could also read much shorter
stretches of DNA on Mars. But simpler and slower gene-sequencing
technologies might also do the job, Carr says.

If the experiment isolates, amplifies and sequences Martian DNA, the
next step will be to determine how the sequence relates to Earth life
and to rule out the possibility of terrestrial contamination, a major
concern with PCR.
      
Contamination test

If Earth and Mars exchanged life 3-4 billion years ago, Mars life will
stand out like an island species that has been isolated from the
mainland. Ruvkun's team will make the call by comparing any 16S
sequences they find on Mars with those known on Earth.

Because of its essential role in building cells' ribosomes, the gene has
barely mutated over the past 4 billion or so years, allowing geneticists
to gauge evolutionary relationships between distantly related organisms.

If the Martian DNA is distantly related to Earth life, its 16S sequence
should plant it near the base of Earth's tree of life. On the other
hand, a sequence that looks closely related to earthly organisms, such
as E. coli or Salmonella bacteria, for instance, would be evidence for
contamination.

Field tests

Team members are wrangling for a spot on a NASA Mars mission tentatively
scheduled for liftoff in 2018. They plan to begin field-testing their
device in Mars-like conditions on Earth, such as the Copahue Volcano
in Argentina or Antarctica's dry valleys, in the next three years.

But the researchers admit they are a long way, not to mention tens of
millions of dollars in funding, from launch. "Our goal is to make this
instrument small enough that they can't say no to put it on a lander,"
Ruvkun says.

Others are taking SETG seriously, too. NASA has renewed the project's
initial grant, and MIT planetary scientist Maria Zuber has taken a
leading role in the team. "Maria is totally in the loop at NASA, and it
lends [SETG] a level of credibility that could never come from us,"
Ruvkun says.

First things first

Norman Pace, a microbiologist at the
University of Colorado in Boulder who studies life in extreme places on
Earth, is more sceptical. He says sequencing DNA on Mars is
"technologically feasible", but he thinks DNA searches should come after
scientists discover other signatures for life on Mars.

"If you have DNA from Mars, it's worth sequencing," Pace says. "But
having DNA from Mars is about as practical at this stage of the game as
having DNA from that planet around Alpha Centauri."

Paul Davies worries that searching for DNA opens too narrow a window to
the past. "If what you're hoping to do is look for traces of past life
on Mars, then DNA isn't a very good biomarker - it's not going to
survive for very long."

Indeed, SETG could only detect existing or recently extinct life on
Mars. Carr puts the outer boundary under 1 million years, though it
could be far less.

Generalist approach

Davies argues that searches for extraterrestrial life should instead
focus on more general features of life. All amino acids that make up
biological proteins, for instance, display a left-handed orientation,
or chirality. "That, to me, is the most urgent thing," he told New
Scientist. "You look for chirality, then mess around with DNA."

An instrument to search for signs of chirality, called Urey, may
launch on Europe's ExoMars lander, which is now set to launch in 2016.
Researchers will try to use its data to determine whether any chirality
found is from life.

Would Urey be able to test, like SETG, whether any life on Mars has a
common origin with that on Earth? Possibly, says instrument team leader
Jeffrey Bada of the University of California, San Diego. "If the
structural variety of amino acids was identical to that on Earth and
they were also left-handed, we might well be related," Bada told New
Scientist.

Definitive test

However, Ruvkun and his colleagues brush aside such concerns, saying
that Martian DNA detection will go hand-in-hand with efforts to find
more generic chemical signatures of life. They also contend that their
experiment would provide a definitive test of the hypothesis that Earth
and Mars exchanged life that still lives on Mars.

And then there's the simple "wow" factor of sending a DNA sequencer to
another planet to search for life.

Michael Finney, a biotechnology entrepreneur on the team who conceived
of SETG along with Ruvkun, says one engineer he approached saw an added
bonus to joining their search for Martian genes.

"He had a reaction a lot of people had: 'I would love to work on this
project because it would give me so much credibility with my
eight-year-old,'" Finney says. "A lot of people on the whole project are
letting their inner eight-year-olds speak."
Received on Thu 09 Apr 2009 06:28:46 PM PDT