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Project Progress

Research conducted during the past year on this project falls into three categories: (1) efforts to understand the energetics of terrestrial hydrothermal ecosystems, and the energetic demands of individual thermophilic and hyperthermophilic microorganisms, (2) predictions of the extent of the subsurface biosphere on the Earth, and (3) connecting the constraints on organic synthesis in hydrothermal and volcanic systems with those extracted from theoretical models of planetary evolution.

Task 1. Energetics of Hydrothermal Ecosystems (Shock). We have made progress in understanding the delicate interplay between thermodynamics and kinetics that generates disequilibrium states in geochemical systems. These disequilibrium states are sources of energy for subsurface organisms. There can be no doubt that the surface of a planet can be irrelevant in determining the potential for life. We are illuminating the connection between quantities of geochemical energy and the biomass that can be supported. In addition, new models of organic synthesis on meteorite parent bodies and icy satellites are revealing the complementary roles of volcanic, impact, and hydrothermal processes in generating and altering the abiotic organic inventory of the solar system.

Task 2. Theoretical Foundation for Organic Synthesis Experiments (Morowitz).
We have developed a search strategy to start with Beilstein on line with three and a half million compounds and look for the subset that would have been generated from aqueous CO2 and reductants in the absence of enzymes. We confine the search to compounds of between one and six carbon atoms on the assumption that we are building up from one-carbon compounds. We then confine the set to a water partition in a water-oil system. Selection is made for highly oxidized molecules starting from CO2. Selection is made for low heats of combustion to be near the starting state of carbons. We eliminate unstable peroxides and carbon triple bonds. This search yields a subset of 153 molecules which contains all 11 molecules of the reductive citric acid cycle. The mining of the Beilstein data base thus suggests the prebiotic synthesis of the reductive Krebs cycle. We are examining the network catalytic set of molecules to see what is special about the Krebs cycle. In addition we are now mining the domain of CHNO molecules to examine the expansion of primordial metabolism to compounds which also contain nitrogen. The paper dealing with CHO molecules has been accepted by PNAS and will be published soon. This material has been presented at the annual meeting of the science advisory board of the Santa Fe Institute.