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).