[meteorite-list] Did Human DNA Hitch a Ride to Mars?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 17 Feb 2010 16:27:30 -0800 (PST)
Message-ID: <201002180027.o1I0RVbD008523_at_zagami.jpl.nasa.gov>

http://www.msnbc.msn.com/id/35428496/ns/technology_and_science-space

Did human DNA hitch a ride to Mars?

Scientists creating instrument that could search soil, ice samples
from Mars

By Michael Schirber
space.com
February 16, 2010

The iguanas of the Galapagos Islands have evolved many unique
characteristics due to their isolation from mainland iguanas. Because
they can't swim long distances, biologists believe that the first
Galapagos iguanas arrived on natural rafts made from vegetation.

The same thing may have happened across the ocean of space. Some
researchers speculate that life on Mars - if there is any - may be
composed of "island species" that were carried away from Earth on
interplanetary meteorites.

Or perhaps both planets were seeded by life from an even more distant
"mainland."

"Earth may not be the center of the DNA-based universe," says Gary
Ruvkun, professor of genetics at Harvard Medical School and
Massachusetts General Hospital.

The idea isn't too crazy. We already have evidence that some
biologically important molecules, such as the ingredients for amino
acids, are delivered by comets. And we know that around 3.5 billion
years ago, meteorite impacts often kicked up rocks from the Earth's
surface and launched them into space.

Microbes and/or bio-molecules may have hitched a ride on one these
cosmic "rafts."

To test this theory ??? called panspermia - Ruvkun and his
colleagues have started a project called the Search for Extraterrestrial
Genomes (SETG, as a play on SETI). They are putting together an instrument
that could go to Mars and search soil or ice samples for the presence of
DNA. If the device finds any, it could then analyze the genetic code to
see if the "Martians" are related to us.

A SETG prototype will have its first field test this year with funding
from NASA's Astrobiology Science and Technology Instrument Development
program.

DNA detection

Some argue that it is too soon to be thinking about DNA on Mars.

"If there were other signs of life, more specifically biomass, I would
applaud DNA analysis," says Norman Pace of the University of Colorado,
Boulder. "Without even trace target biomass, talking about DNA sequences
seems premature to me."

But Ruvkun argues that his team's technique can detect a single DNA
molecule in a sample, whereas other tests for biology - such as
identifying chemical constituents with mass spectrometry - are not
nearly as sensitive.

"It's very hard to detect a single molecule with chemical analysis,"
concurs Harry Noller from the University of California at Santa Cruz.
"But you can uniquely amplify DNA," so that its signal clearly stands out.

Immutable DNA

In order to amplify small traces of potential alien DNA, Ruvkun
and his collaborators have looked for a stretch of DNA that would likely
be conserved in both Martians and Earthlings.

They believe this common thread should be in the 16S ribosomal RNA gene,
which is vital to the protein-making process in cells. This gene has
regions of its sequence that have barely changed over billions of years
of evolution.

In fact, short segments in the 16S ribosomal RNA sequence are exactly
identical in more than 100,000 species that have so far had their
ribosome genes analyzed.

"There's no way to have a mutation here and live to tell about it," says
Noller, who is not part of the SETG team.

As a consequence, any Martians that share our genetic heritage will
presumably carry the 16S ribosomal RNA gene with the same conserved
pieces that all of us Earthlings have.

A primer for life

The proposed strategy is for the SETG instrument to receive a Martian
sample and add small extracts from the 16S ribosomal RNA gene as
"primers" for DNA replication. If the sample contains DNA and if some
part of that DNA's genetic code matches the primer's, then a suite of
chemical reactions will produce a million or so copies of the sample's DNA.

The amplified DNA can be detected with special markers and part of its
code can be sequenced in order to identify what sort of life-form is the
owner of this DNA.

If the sample were contaminated by Earthling DNA, then the SETG
researchers should be able to recognize signatures in the sequenced code
that will pinpoint whether the contamination comes from a human or a
bacteria or something else familiar to us.

But if nothing on Earth matches the observed sequence, Ruvkun and his
colleagues will claim to have found our long-lost Martian cousins.

Ruvkun and his colleagues have built a prototype of their DNA analyzer
and are in the midst of calibrating it. The team will travel to
Argentina's Copahue Volcano, which is considered to be one of the most
Mars-like environments on Earth. There, they will test whether the
prototype can sequence the DNA of some of the hearty microbes that live
in the acidic runoff from the volcano.
Received on Wed 17 Feb 2010 07:27:30 PM PST