Testing the habitability of alkaline hydrothermal vents in a simulated Hadean ocean environment

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The overarching research aim of the proposed work is to use controlled laboratory experiments to investigate the habitability of alkaline hydrothermal vents (AHVs) in simulated Hadean conditions that are hypothesized to play a critical, but as-of-yet unconstrained, role in planetary habitability. I propose to address this challenge by applying a novel experimental setup that will enable us to directly address questions regarding planetary habitability using controlled experiments. My lab has developed a new experimental setup for producing alkaline hydrothermal chimney structures under simulated Hadean conditions in an anaerobic chamber. Dark green chimney structures precipitate out of an acidic iron “ocean” (an analog for the Hadean ocean) as hydrothermal alkaline fluids mix are pumped in from the bottom of the “ocean” analog, simulating a hydrothermal chimney at the Hadean seafloor. Preliminary data show that the chimneys consist predominantly of iron (oxy)hydroxides and iron sulfides, and produce abiotic H2 gas production ranging 10-400 µM H2 over a 24-hour period enabling us to test hypotheses surrounding abiotic H2 as a geological energy source for methanogenic archaea in Hadean AHVs. I propose to use mesophilic and hyperthermophilic H2-oxidizing methanogens as model organisms, to test whether the abiotic H2 produced in the AHV chimneys can promote growth of these microbes from 20-80 degrees C. This will establish boundary conditions supporting life in Hadean hydrothermal settings producing abiotic H2, and habitable planetary environments. Controlled experiments are proposed that will test whether H2-limitation in these microbes can be overcome via abiotic H2 produced by AHV chimneys in a simulated Hadean environment. We will use gene expression techniques to constrain the biological mechanisms behind the habitability of the simulated Hadean chimney environment, namely to examine the potential for biofilm formation on the chimney surface. We will use thin sections and microscopy to determine the preferred location of the chimney structure that is colonized and how this relates to pH gradients and methanogenic metabolic processes compared between ‘free living’ and chimney-associated cells. The proposed work seeks to confirm with controlled experimentation that the abiotic H2 produced from the AHV chimneys can indeed fuel microbial methanogenesis in a simulated Hadean environment as proposed by numerous theories, constraining the temperature and inorganic chemical conditions that promote planetary habitability in a simulated Hadean setting.