LExEn: Experimental Studies on Hydrogen Biogeochemistry in Anoxic Environments

9713967雷堡氢在微生物新陈代谢中起核心作用，并在低浓度下保持动力学和热力学。氢分压是缺氧系统的主要控制因素，可由生物和非生物提供。氢可以非常灵敏地检测和测量，但在自然系统上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生产和消费。到目前为止，大多数关于氢的研究都涉及到共培养的使用，在这种情况下，两种生物被用来设定和控制氢分压。该项目包括开发和应用一种设备，该设备将允许设置和控制培养系统的氢分压。通过上游-下游气体测量检测到的培养容器中发生的速率测量和气体成分变化将用于研究在一系列氢分压下与甲烷生成、厌氧甲烷氧化(反甲烷生成)和同位素分馏相关的变化。该项目有三个目标：1)建立和运行一个培养系统，其中氢分压可以设置并保持在不同的水平。方法将是设置系统的氢分压，并研究微生物在一系列分压下的行为。2)利用该装置验证甲烷厌氧氧化是由低氢分压下的产甲烷菌进行反向操作的假设。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中的样本进行研究。3)测定不同生长速率和培养条件下的碳、氢稳定同位素分馏系数。分馏系数是可用的，但很难普遍适用，因为它们是在一系列条件下获得的。在这项研究中开发的装置将允许在一系列生长速度和衬底条件下进行上游-下游气相采样和同位素分馏系数的测定。除了解决导致厌氧甲烷氧化的微生物和机制这一遗留问题外，该方法还将允许在一系列条件下测定纯和混合培养物上甲烷生成和反甲烷生成的同位素(C和H)分馏系数。这项研究开发的氢浓度控制技术可能对极端缺氧环境中其他生物群的氢代谢和种间氢转移的研究有用。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.