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

拟议工作的首要研究目标是使用受控实验室实验来调查模拟Hadean条件下碱性热液喷口（AHV）的可居住性，假设这些条件在行星可居住性中发挥关键但尚未受到约束的作用。 我建议通过应用一种新的实验装置来解决这一挑战，这将使我们能够使用受控实验直接解决有关行星可居住性的问题。 我的实验室开发了一种新的实验装置，用于在厌氧室中模拟冥古宙条件下生产碱性水热烟囱结构。 深绿色烟囱结构从酸性铁“海洋”（类似于冥古宙海洋）中沉淀出来，因为热液碱性流体混合物从“海洋”模拟物的底部泵入，模拟冥古宙海底的热液烟囱。 初步数据显示，烟囱主要由铁（氧）氢氧化物和铁硫化物组成，并在24小时内产生10-400 µM H2的非生物H2气体产量，使我们能够测试围绕非生物H2作为Hadean AHV中产甲烷古菌的地质能源的假设。 我建议使用嗜中温和超嗜热H2氧化产甲烷菌作为模式生物，以测试AHV烟囱中产生的非生物H2是否可以促进这些微生物在20-80 ℃的生长。 这将建立边界条件，支持在冥古宙热液环境中产生非生物H2和可居住的行星环境中的生命。 控制实验提出，将测试是否H2限制在这些微生物可以克服通过非生物H2产生的AHV烟囱在模拟冥古宙环境。 我们将使用基因表达技术来限制模拟冥古宙烟囱环境可居住性背后的生物机制，即检查烟囱表面形成生物膜的可能性。 我们将使用薄切片和显微镜来确定被殖民化的烟囱结构的优选位置，以及这与“自由生活”和烟囱相关细胞之间的pH梯度和产甲烷代谢过程的关系。 拟议的工作旨在通过受控实验证实，AHV烟囱产生的非生物H2确实可以在模拟Hadean环境中为微生物甲烷生成提供燃料，正如许多理论所提出的那样，限制了在模拟Hadean环境中促进行星可居住性的温度和无机化学条件。

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.