[25]
DNA-based
life detection on Earth and Mars: polymerase chain
reaction optimization using short ribosomal primers.
N.M. Vahora1,
C.E. Carr2, M.T. Zuber2, and G. Ruvkun3,4
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1Department of Civil and
Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA
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2Department of Earth,
Atmospheric and Planetary Sciences, Massachusetts Institute of
Technology, Cambridge, MA. 3Department
of Genetics, Harvard University, Cambridge, MA.
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4Department of Molecular
Biology, Massachusetts General Hospital, Boston, MA.
A
reasonable case can be made that life (past or present) on Mars may be
ancestrally
related to life on Earth because of significant meteoritic exchange
between
Earth and Mars. On Earth, the DNA-based polymerase chain reaction (PCR)
provides a simple, standard, and powerful method to detect life. A soil
sample
from an extreme environment can be surveyed for the signature of life,
a DNA
fragment of a gene that is universal to life on Earth. Of the
approximately 500
“universal genes” carried in the DNA of every known living organism,
the 16S
small subunit ribosomal RNA gene shows some of the highest levels of
conservation at the base pair level. While some regions are conserved
across
all known life, other regions vary significantly, making 16S a good
chronometer
by which to build a tree of life and to classify organisms on the basis
of their
16S sequences. By targeting the most conserved regions of 16S we can
create
“universal primers” able to amplify DNA from any known living organism;
however, these primers must be short enough to achieve universal
sensitivity
but long enough to primarily target 16S. Using primers identified from
analysis
of base pair conservation, we are validating candidate primers against
metagenomic libraries to identify primers with the highest signal to
noise
ratio. This optimization may result in a protocol able to detect and
classify
new and interesting organisms, whether on Earth or Mars.
(Supported by NASA
grant NNG05GK27G.)
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