14:55 〜 15:15
[BBG01-05] Co-evolution of life environment through Earth history: insights from theoretical modeling and genetic data analysis
★Invited Papers
キーワード：シアノバクテリア、全球凍結、大酸化イベント
Geological records suggest that atmospheric oxygen concentrations rose sharply during the Paleoproterozoic and the Neoproterozoic, respectively, and that a major glacial period called snowball Earth events, in which the entire globe was covered with ice, occurred during the same period. These changes in the surface environment must have interacted with the evolution of photosynthetic organisms. Cyanobacteria irreversibly change the composition of the Earth's atmosphere through oxygen-evolving photosynthesis, and their evolution has been directly affected by climate change. The presenter has been studying the interaction between cyanobacterial evolution and the global environment by interdisciplinary approach, combining the numerical modeling of biogeochemical cycles, molecular phylogenetic analysis, and reconstruction of ancestral proteins.
Numerical modeling studies simulating the post-glacial environment in the Paleoproterozoic revealed that a climatic jump to a super greenhouse environment occurred immediately after the snowball Earth, and nutrient fluxes to the oceans increased due to accelerated weathering of the continental crust. In the nutrient rich ocean, photosynthetic activity of cyanobacteria increased, which resulted in a shift from oxygen-poor to oxygen-rich environments. This is one example of how environments, climate and the chemical composition of the atmosphere and ocean, affected by the changes in biosphere.
On the other hand, changes in environments can also affect biosphere, which is assessed by molecular phylogenetic analysis and reconstruction of ancestral proteins. By reconstructing ancestral Nucleoside diphosphate kinase (NDK) proteins in the laboratory and measuring their thermostability, the transition of the optimal growth temperature of the ancestor organism can be estimated. The presenters' analysis of ancestral marine cyanobacteria from the Neoproterozoic to the Phanerozoic revealed that they maintained optimal growth temperatures of ~35 C, in response to long-term trends in ocean temperature. The results imply that it is important to analyze how the ancestral marine cyanobacteria acquired tolerance to extreme cold events such as snowball Earth events.
Expanding the method of ancestral protein reconstruction not only to changes in the thermal environment but also to geochemical environmental changes is expected to bring significant progress in elucidating the history of life on Earth. To clarify the evolution of organisms' adaptation to changes in atmospheric oxygen concentrations, the presenter is also attempting to reconstruct the ancestral antioxidant enzyme, superoxide dismutase (SOD). Molecular phylogenetic analysis suggests that antioxidant enzymes, which are essential for adaptation to increased oxygen concentrations in the environment, have already been acquired in the early stages of cyanobacterial evolution. The future prospects of SOD ancestral protein type reconstruction experiments will also be presented.
Numerical modeling studies simulating the post-glacial environment in the Paleoproterozoic revealed that a climatic jump to a super greenhouse environment occurred immediately after the snowball Earth, and nutrient fluxes to the oceans increased due to accelerated weathering of the continental crust. In the nutrient rich ocean, photosynthetic activity of cyanobacteria increased, which resulted in a shift from oxygen-poor to oxygen-rich environments. This is one example of how environments, climate and the chemical composition of the atmosphere and ocean, affected by the changes in biosphere.
On the other hand, changes in environments can also affect biosphere, which is assessed by molecular phylogenetic analysis and reconstruction of ancestral proteins. By reconstructing ancestral Nucleoside diphosphate kinase (NDK) proteins in the laboratory and measuring their thermostability, the transition of the optimal growth temperature of the ancestor organism can be estimated. The presenters' analysis of ancestral marine cyanobacteria from the Neoproterozoic to the Phanerozoic revealed that they maintained optimal growth temperatures of ~35 C, in response to long-term trends in ocean temperature. The results imply that it is important to analyze how the ancestral marine cyanobacteria acquired tolerance to extreme cold events such as snowball Earth events.
Expanding the method of ancestral protein reconstruction not only to changes in the thermal environment but also to geochemical environmental changes is expected to bring significant progress in elucidating the history of life on Earth. To clarify the evolution of organisms' adaptation to changes in atmospheric oxygen concentrations, the presenter is also attempting to reconstruct the ancestral antioxidant enzyme, superoxide dismutase (SOD). Molecular phylogenetic analysis suggests that antioxidant enzymes, which are essential for adaptation to increased oxygen concentrations in the environment, have already been acquired in the early stages of cyanobacterial evolution. The future prospects of SOD ancestral protein type reconstruction experiments will also be presented.