Life Under Infrared Skies

I know that interstellar colonization is probably a very long way down
the road, but anyway the discovery of clorophyl "tuned" to infrarred
has obvious implications in astrobiology considerations for red dwarfs,
as well as (thinking as a space colonist :) agriculture in habitats and
planets around them.

Sent to you by Lucio via Google Reader: Life Under Infrared Skies via
Centauri Dreams by Administrator on 2/13/08
So far we know of only one place in the cosmos that has life, our own
Earth. That makes the study of interesting organisms, and in particular
the so-called 'extremophiles' that stretch our understanding of livable
habitats, a key part of astrobiology. Finding an organism living around
a deep-water vent on the ocean floor doesn't prove life exists in such
environments on other worlds, but by understanding the limits of the
possible, we're learning more about where and how to look.

And sometimes we find unusual life forms in seemingly benign places
like Australia's Great Barrier Reef, which brings us to Acaryochloris
marina. That tongue twister identifies a bacterium that is unusual
because it uses a rare type of chlorophyll -- chlorophyll d -- to take
advantage of near infrared long wavelength light. Acaryochloris marina
is actually a cyanobacterium, meaning a bacterium that use
photosynthesis to derive its energy. Its huge genome (8.3 million base
pairs) has now been sequenced for the first time, with interesting
implications for plant research and, conceivably, astrobiology. Thanks
to Vincenzo Liguori for sending a link to Astrobiology Magazine's
coverage of this work.

Jeffrey Touchman (Arizona State), lead author of the paper in question,
sees applications in various forms of plant research:

"Chlorophyll d harvests light from a spectrum of light that few other
organisms can, and that enables this organism to carve out its own
special niche in the environment to pick up far-red light. The
agricultural implications could be significant. One could imagine the
transfer of this biochemical mechanism to other plants where they could
then use a wider range of the light spectrum and become sort of 'plant
powerhouses,' deriving increased energy by employing this new
photosynthetic pigment."

Space applications? Productive crops for space stations are one
possibility. But looking outward, the gaze is inevitably drawn to the
75 to 80 percent of stars in the Milky Way that are M-dwarfs.
Speculation about habitable planets around these stars heated up with
the controversy over Gliese 581's planets, but the broader issue
addressed by finds like this is that Earth life adapted to the near
infrared may be showing us the directions life could take in other
exotic environments. After all, most of the radiation an M-dwarf emits
is in the infrared.

Just how chlorophyll d is formed depends upon an enzyme that causes the
needed chemical changes to distinguish it from the more common
chlorophyll a and b, among other types of chlorophyll. The research
team, working at Arizona State and Washington University (St. Louis)
will test to see if organisms can be induced to produce chlorophyll d
with candidate genes inserted. If so, genetically altered plants could
result that take advantage of a wider range of available light. In the
meanwhile, our ideas about habitable zones get another nudge.

It would be tricky to come up with a form of life, even on a planet
circling a red dwarf, more unusual than Acaryochloris marina. The
cyanobacterium lives in symbiosis with the sea squirt, a marine animal
something like a sponge that attaches itself to rocks below the water's
surface. Our cyanobacterium lives beneath the sea squirt, absorbing its
needed infrared through.the creature's tissues. Now that's exotic!

The paper is Touchman et al., "Niche adaptation and genome expansion in
the chlorophyll d-producing cyanobacterium Acaryochloris marina,"
Proceedings of the National Academy of Sciences Vol. 105, No. 6 (12
February, 2008), 2005-2010 (abstract).

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