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Project Progress

Photoacoustic measurements of thermodynamic efficiency of photon energy use in Acaryochloris marina (Kiang, Blankenship, Mielke, collaborators at Rockefeller University, City College of New York).
Under funding from the NAI Director’s Discretionary Fund (DDF) 2008, we have been conducting measurements the efficiency of photon energy storage by wavelength in Photosystem I in whole intact cells of the cyanobacterium Acaryochloris marina. A. marina is the only known organism to have chlorophyll d (Chl d) to use photons in the far-red (713-715 nm) and near-infrared (740 m), whereas all other oxygenic photosynthetic organisms use chlorophyll a (Chl a) to absorb at 680 nm and 700 nm. We have obtained preliminary measurements indicating that A. marina may be exhibiting lower efficiencies hence lower quantum yields compared to Chl a-utilizing organisms, i.e. the red wavelengths could be at a fundamental limit for oxygenic photosynthesis and thus constrain what is plausible on extrasolar planets. Confirmation with further measurements continues, after a laser failure in January 2009.

Complementing these lab studies, NAI postdoctoral fellow Steven Mielke is now also using the Multi-Conformer Continuum Electrostatics (MCCE) computer program of a new collaborator, Dr. Marilyn Gunner, at City College of New York to model redox potentials along the electron transfer pathway in Photosystem II with Chl a versus Chl d. This theoretical work will predict, confirm, and/or explain results of the photoacoustic measurements. In October 2009, the project was awarded additional NAI DDF funds to enhance the lab studies with measurements on purified complexes of Photosystems I and II.

Conferences:
Kiang, N.Y., S.P. Mielke, D. Mauzerall, R.E. Blankenship. “Limits of photosynthesis:
non-Earthlike target biosignatures, “Pathways Toward Habitable Planets, Barcelona, Spain, 14-18 September 2009,” oral presentation.
Kiang, N.Y. “Earth remote sensing for the search for life elsewhere in the universe: discerning spectral signatures of photosynthesis on extrasolar planets,” 2nd HyspIRI Science Workshop, Sheraton Hotel, Pasadena, August 11-13, 2009, poster.
Kiang, N.Y. “Astrobiology of Photosynthesis: Color Limits for Life Adapted to Other Stars and Atmospheres,” Kavli Symposium, Beckman Center, University of California, Irvine, November 6-8, 2008, Invited talk.
Mielke, SP, NY Kiang, RE Blankenship, D Mauzerall. “Energy storage of oxygenic photosynthesis in the cyanobacterium, Acaryochloris marina, investigated by photoacoustics,” Eastern Regional Photosynthesis Conference (ERPC), Marine Biological Laboratory, Woods Hole, MA, April 17 – 19, 2009, poster.
Mielke, SP , NY Kiang, RE Blankenship, D Mauzerall. “Energy storage of oxygenic photosynthesis in the cyanobacterium, Acaryochloris marina, investigated by photoacoustics,” Gordon Research Conference – Photosynthesis, Bryant University, Smithfield, RI, June 28 – July 3, 2009, poster.
Mielke, SP , NY Kiang, RE Blankenship, D Mauzerall. “Energy storage of oxygenic photosynthesis in the cyanobacterium, Acaryochloris marina, investigated by photoacoustics,” Weizmann UK Symposium – Light Energy for a Brighter Future, Imperial College and Royal Geographical Society, London, UK, July 6 – 7, 2009, poster.
Mielke. SP. “Photosynthetic Electron Transfer in the Cyanobacterium, Acaryochloris marina,” NAI Executive Council Meeting, Yellowstone National Park, Wyoming, September 10 – 11, 2009, talk.