By Rachel Ehrenberg, Science News
A new kind of chlorophyll that catches sunlight from just beyond the red end of the visible light spectrum has been discovered. The new pigment extends the known range of light that is usable by most photosynthetic organisms. Harnessing this pigment’s power could lead to biofuel-generating algae that are super-efficient, using a greater spread of sunlight than thought possible.
“This is a very important new development, and is the first new type of chlorophyll discovered in an oxygenic organism in 60 years,” says biological chemist Robert Blankenship of Washington University in St. Louis.
The newfound pigment, dubbed chlorophyll f, absorbs light most efficiently at a wavelength around 706 nanometers, just beyond the red end of the visible spectrum, researchers report online August 19 in Science. This unique absorbance appears to occur thanks to a chemical decoration known as a formyl group on the chlorophyll’s carbon number two. That chemical tweak probably allows the algaelike organism that makes chlorophyll f to conduct photosynthesis while living beneath other photosynthesizers that capture all the other usable light.
“In nature this very small modification of the pigment happens, and then the organism can use this unique light,” says molecular biologist Min Chen of the University of Sydney in Australia. Chen and her colleagues identified the new pigment in extracts from ground-up stromatolites, the knobby chunks of rock and algae that can form in shallow waters. The samples were collected in the Hamelin pool in western Australia’s Shark Bay, the world’s most diverse stromatolite trove.
Previously there were four known chlorophylls made by plants and other photosynthesizing organisms that generate oxygen: a, b, c and d. Chlorophyll a, the standard green type, is found in photosynthesizers from algae to higher plants. It absorbs mostly blue light around 465 nanometers and red light around 665 nanometers (it reflects green light, hence plants look green). Chlorophylls b and c are found in fewer organisms and absorb light in a similar range as chlorophyll a does, but shifted a bit. Chlorophyll d, found in a specific group of cyanobacteria, absorbs the most light at roughly 697 nanometers, a slightly shorter wavelength than the absorption of the new chlorophyll.
While some bacteria make chlorophyll-like pigments that absorb even longer wavelengths of light, these creatures aren’t harnessing light to split water, the step in photosynthesis that generates oxygen. Scientists didn’t think that wavelengths absorbed by chlorophyll f would have enough oomph to split water either, but it turns out they do, says Chen.
“This challenges our conception of the limit of oxygenic photosynthesis,” she says.
The find may also enable scientists to engineer algae that are more efficient producers of oil for biofuels, says algae biologist Krishna Niyogi of the University of California, Berkeley. Microbes bearing the new chlorophyll could soak up rays that most microbes can’t make use of.
There is still much to be learned about the new type of chlorophyll and the organisms that make it, Niyogi says. Chlorophyll f was extracted from the ground-up stromatolites along with a lot of chlorophyll a. It isn’t clear what creature was making chlorophyll f, but evidence points to a filamentous cyanobacterium. This cyanobacterium might use both chlorophylls, or perhaps just f.
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