LExEn: Experimental Studies on Hydrogen Biogeochemistry in Anoxic Environments

小行星9713967 氢在微生物代谢中起着核心作用，并且在动力学和动力学上维持在低浓度。氢气分压是缺氧系统的主要控制因素，可以通过生物和非生物方式供应。氢可以以很高的灵敏度被检测和测量，但是在自然系统上进行可靠的测量是困难的，因为通过采样破坏微环境可能导致氢的产生和消耗。迄今为止，大多数关于氢的研究都涉及共培养的使用，其中使用两种生物体来设定和控制氢分压。该项目包括一种装置的开发和应用，该装置将允许设置和控制培养系统的氢分压。速率测量和气体成分的变化发生在培养容器中检测的上游-下游气体测量将被用来研究甲烷生成，厌氧甲烷氧化（反向甲烷生成）和同位素分馏下的氢分压的范围内与两者相关。 该项目有三个目标：1）建立和操作培养系统，其中氢分压可以设定并维持在不同的水平。该方法将设定系统的氢分压，并研究在一定范围的分压下微生物的行为。 2)利用该装置来验证甲烷厌氧氧化是由甲烷菌在低氢分压下反向操作进行的假设。将对产甲烷菌的纯培养物、产甲烷菌和硫酸盐还原菌的混合培养物以及已知发生厌氧氧化的自然环境样品进行研究。 3)在一定的生长速率和培养条件下测定碳和氢稳定同位素分馏因子。分馏因子是可用的，但由于获得它们的条件范围而难以普遍应用。在这项研究中开发的设备将允许上游下游气相采样和同位素分馏因子的测定范围内的生长速率和基板条件。 除了解决负责厌氧甲烷氧化的生物体和机制的剩余问题之外，这种方法将允许在一系列条件下在纯培养物和混合培养物上测定甲烷生成和反向甲烷生成的同位素（C和H）分馏因子。在这项研究中开发的控制氢浓度的技术可能是有用的在极端缺氧环境中的氢代谢和物种间的氢转移的其他群体的生物体的研究。 资金由生物科学局、地球科学局和数学和物理科学局多学科活动办公室提供。

9713967 Reeburgh Hydrogen plays a central role in microbial metabolism and is kinetically and thermodynamically maintained at low concentrations. Hydrogen partial pressure is a major control on anoxic systems, and can be supplied biologically and abiologically. Hydrogen can be detected and measured with great sensitivity, but reliable measurements on natural systems are difficult, as disruption of microenvironments by sampling may lead to production and consumption hydrogen. Most studies on hydrogen to date have involved the use of co-cultures, where two organisms are used to set and control the hydrogen partial pressure. This project includes the development and application of an apparatus that will permit setting and controlling the hydrogen partial pressure of a culture system. Rate measurements and gas composition changes occurring in the culture vessel detected by upstream-downstream gas measurements will be used to study methanogenesis, anaerobic methane oxidation (reverse methanogenesis) and isotope fractionation associated with both under a range of hydrogen partial pressures. This project has three goals: 1) To build and operate a culture system in which the hydrogen partial pressure can be set and maintained at varying levels. The approach will be to set the system's hydrogen partial pressure and study microbial behavior under a range of partial pressures. 2) To use this apparatus to test the hypothesis that anaerobic methane oxidation is conducted by methanogens operating in reverse at low hydrogen partial pressures. Studies on pure cultures of methanogens, mixed cultures of methanogens and sulfate reducers, and samples from natural environments where anaerobic oxidation is known to occur will be carried out. 3) To determine C and H stable isotope fractionation factors under a range of growth rate and culture conditions. Fractionation factors are available, but are difficult to apply generally because of the range of conditions under which they were obtained. The apparatus developed in this study will permit upstream-downstream gas phase sampling and determination of isotope fractionation factors under a range of growth rate and substrate conditions. In addition to settling the remaining question of the organisms and mechanisms responsible for anaerobic methane oxidation, this approach will permit determination of isotope (C and H) fractionation factors for both methanogenesis and reverse methanogenesis on pure and mixed cultures under a range of conditions. The techniques for controlling hydrogen concentration developed in this study may be useful in studies of hydrogen metabolism and interspecies hydrogen transfer by other groups of organisms in extreme anoxic environments. Funding is being provided by the Directorate for Biological Sciences, the Directorate for Geosciences and the Office of Multidisciplinary Activities of the Directorate for Mathematical and Physical Sciences.