Open Questions on the Origin of Life at Anoxic GeothermalFields

摘要

We have recently reconstructed the ‘hatcheries’ of the first cells by combining geochemical analysis with phylogenomic scrutiny of the inorganic ion requirements of universal components of modern cells (Mulkidjanian et al.: Origin of first cells at terrestrial, anoxic geothermal fields. Proc Natl Acad Sci USA 2012, 109:E821–830). These ubiquitous, and by inference primordial, proteins and functional systems show affinity to and functional requirement for K⁺, Zn²⁺, Mn²⁺, and phosphate. Thus, protocells must have evolved in habitats with a high K⁺/Na⁺ ratio and relatively high concentrations of Zn, Mn and phosphorous compounds. Geochemical reconstruction shows that the ionic composition conducive to the origin of cells could not have existed in marine settings but is compatible with emissions of vapor-dominated zones of inland geothermal systems. Under anoxic, CO2-dominated atmosphere, the ionic composition of pools of cool, condensed vapor at anoxic geothermal fields would resemble the internal milieu of modern cells. Such pools would be lined with porous silicate minerals mixed with metal sulfides and enriched in K⁺ions and phosphorous compounds.Here we address some questions that have appeared in print after thepublication of our anoxic geothermal field scenario. We argue that anoxicgeothermal fields, which were identified as likely cradles of life by using atop-down approach and phylogenomics analysis as a tool, could providegeochemical conditions similar to those which were suggested as most conducivefor the emergence of life by the chemists who pursuit the complementarybottom-up strategy.