LExEn: Experimental Studies on Hydrogen Biogeochemistry in Anoxic Environments

氢在微生物代谢中起着核心作用，并且在低浓度下保持动力学和热力学。氢气分压是对缺氧系统的一个主要控制，可以生物和非生物供应。氢可以以很高的灵敏度检测和测量，但对自然系统进行可靠的测量是困难的，因为采样对微环境的破坏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使用共培养，即使用两种生物来设置和控制氢的分压。本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。通过上下游气体测量检测到的速率测量和培养皿中发生的气体成分变化将用于研究在一定范围的氢分压下的甲烷生成、厌氧甲烷氧化（反甲烷生成）以及与两者相关的同位素分馏。本项目有三个目标：1)建立并运行一个氢气分压可设定并维持在不同水平的培养系统。该方法将设置系统的氢气分压，并研究微生物在一定分压范围内的行为。2)利用该装置验证了低氢分压下产甲烷菌反向操作厌氧甲烷氧化的假设。将进行产甲烷菌纯培养、产甲烷菌和硫酸盐还原剂混合培养以及已知发生厌氧氧化的自然环境样品的研究。3)测定不同生长速率和培养条件下碳、氢稳定同位素分馏因子。分馏因子是可用的，但由于获得分馏因子的条件范围不同，因此难以普遍应用。本研究开发的仪器将允许在一定的生长速率和底物条件下进行上下游气相采样和同位素分馏因子的测定。除了解决微生物和厌氧甲烷氧化机制的剩余问题外，该方法还将允许在一系列条件下在纯和混合培养物上测定甲烷生成和反甲烷生成的同位素（C和H）分馏因子。本研究发展的氢浓度控制技术可能对研究极端缺氧环境下其他生物群体的氢代谢和种间氢转移有帮助。资金由生物科学理事会、地球科学理事会和数学和物理科学理事会的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.