Collaborative Research: Biochemical, Genetic, Metabolic and Isotopic Constraints on an Ancient Thiobiosphere

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Chemical bonds between phosphorus and oxygen are important in building DNA and RNA, and also in supplying modern cells with energy. It is not known, however, whether the first life forms had the same chemistry, and early life in particular may have run on sulfur instead of phosphorus. This project will work backwards from the traces of this sulfur-based chemistry in modern life to reconstruct the role of sulfur-oxygen bonds in early ecosystems. Predictions made from this approach will be compared to the carbon and sulfur isotope record in 2.5 billion year old rocks. We will use the astrobiology social media platform (SAGANet) for the conversations with public about this project and other studies of evolution of life on Earth. Phosphate esters, such as nucleotide triphosphates, diphosphates, and pyrophosphate, are the central component of energy metabolism in all living cells. It is not known, however, whether they were of similar paramount importance at the origin of life or in the first cells, or whether another kind of chemistry was playing the same role there. Considerations from geochemistry, molecular evolution, and systems biology imply that thioesters - high-energy bonds based on sulfur instead of phosphorus - may have supplied energy in the first metabolisms on Earth. This project will develop a broad and detailed understanding of the natural history of thioester utilization, working backwards to reconstruct ancient biochemistry from contemporary metabolism, and simultaneously examining pre-biological chemistries that can couple thioester formation and degradation. These two lines of study will allow the research team to infer the carbon and sulfur isotopic signatures of important metabolic pathways in a putative early thiobiosphere, and test whether these signatures are preserved in the 2.5 billion year old geological record. The results of this project should be of broad interest, and the project will engage with the scientific community and the public through journal publications as well as an established astrobiology social media platform (SAGANet). Select high school serving communities traditionally underrepresented in science will be reached through semester-long programs led by SAGANet graduate student mentors and facilitated by the investigators of this project.