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Project Progress

Work on the origin and early evolution of photosynthesis is carried out by a highly interdisciplinary team of scientists from several different institutions. The overall theme is understanding the origin and early evolution of photosynthesis and its effect on the biosphere. This year four main aspects have been emphasized: (1) whole genome comparative analyses of photosynthetic organisms, (2) the search for phototrophs in non-solar environments around hydrothermal vents, (3) field and laboratory studies of photosynthetic organisms in thermophilic and iron-rich environments and (4) Biochemical analysis of primitive phototrophic organisms. Each of these projects has seen significant progress, as described below.

• Whole genome comparative analyses of photosynthetic organisms: Whole genome sequences have recently become available for representatives from all major groups of photosynthetic organisms. Analysis of these genomes using molecular evolution techniques reveals that large-scale horizontal gene transfer has taken place. The results indicate that the evolution of photosynthesis has been a complex non-linear process. Additional work has involved the development of new analytical methods for genome analysis.
• Search for phototrophs in non-solar environments around hydrothermal vents: Deep sea hydrothermal vents emit a small amount of light that arises from both thermal and nonthermal sources. In December 2001 a team of scientists made several Alvin dives to the hydrothermal vents of the Nine North vent system of the East Pacific Rise. Samples collected are in the process of being analyzed. Photosynthetic organisms cultured from samples collected near the vents are now in laboratory culture. Control experiments to determine if these organisms grew in the vent environment or are contaminants arising from surface water are currently being conducted. Additional work that involved light measurements at hydrothermal vents along the Mid-Atlantic Ridge gave results similar to those from vents in the Pacific.
• Field and laboratory studies of photosynthetic organisms in iron-rich environments: Our studies indicate that some photosynthetic organisms can utilize reduced iron as an electron donor, a finding that may have importance for understanding the origin of the banded iron formations and the rise of oxygen on Earth. Both laboratory and field studies have been carried out, and some mutants of proteins that are potential candidates for Fe-oxidizing complexes have been made and are presently being analyzed. Preliminary Fe isotope measurements have been made on organisms at Yellowstone National Park.
• Biochemical analysis of primitive phototrophic organisms: Extensive biochemical analysis of a number of proteins from the early-branching thermophilic photosynthetic organism Chloroflexus aurantiacus have been carried out. Proteins studied include superoxide dismutase, auracyanin (a copper protein thought to be involved in photosynthetic electron transfer) and several multisubunit cytochrome electron transfer complexes. These studies give insight to the metabolism and reactive oxygen protection strategies of this organism.