A bacterium that harvests far-red light by making a rare form of chlorophyll (chlorophyll d) has revealed its genetic secrets, according to a team of researchers who recently sequenced the bacteria's genome.
The researchers, from Arizona State University and Washington University, St. Louis, report in the current online edition (Feb. 4) of the Proceedings of the National Academy of Sciences, that they have sequenced the genome of the cyanobacterium, Acaryochloris marina, which through its production of chlorophyll d can absorb “red edge,” near infrared long wavelength light -- light that is invisible to the naked eye. Acaryochloris marina has a massive genome (8.3 million base pairs) and is among the largest of 55 cyanobacterial strains in the world. It is the first chlorophyll-d containing organism to be sequenced.
The advance has applications in plant research, said Jeffrey Touchman, an assistant professor ASU's School of Life Sciences and lead author of the paper, “Niche adaptation and genome expansion in the chlorophyll d-producing cyanobacterium Acaryochloris marina.”
“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,” Touchman explained. “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.”
There is a bioenergy link to this work, said Touchman, who is a member of ASU's Center for Bioenergy and Photosynthesis. It could be used for crops that are turned into fuels or to generate biomass.
Touchman worked with Robert Blankenship of Washington University on the sequencing project, which involved collaborators from Australia and Japan. Touchman also has an appointment with Translational Genomics Research Institute (TGen), Scottsdale, Ariz., where he operates a high-throughput DNA sequencing facility. The work is supported by the National Science Foundation.
Blankenship said with every gene of Acaryochloris marina now sequenced and annotated, the immediate goal is to find the enzyme that causes a chemical structure change in chlorophyll d, making it different from the more common chlorophyll a, and b, but also from about nine other forms of chlorophyll.
“The synthesis of chlorophyll by an organism is complex, involving 17 different steps in all,” Blankenship said. “Someplace near the end of this process, an enzyme transforms a vinyl group to a formyl group to make chlorophyll d. This transformation of chemical forms is not known in any other chlorophyll molecules.”
Touchman and Blankenship said they have some candidate genes they will test. They plan to insert these genes into an organism that only makes chlorophyll a. If the organism learns to synthesize chlorophyll d with one of the genes, the mystery of chlorophyll d synthesis will be solved, and then the excitement will begin.
The researchers said harvesting solar power through plants or other organisms that would be genetically altered with the chlorophyll d gene could make them “solar power factories” that generate and store solar energy. Consider a seven-foot tall corn plant genetically tailored with the chlorophyll d gene to be expressed at the very base of the stalk. While the rest of the plant synthesized chlorophyll a, absorbing short wave light, the base is absorbing “red edge” light in the 710 nanometer range.