Institute of Environment and Resources, Bygningstorvet, Bilding 115, Technical University of Denmark, DK-2800 Lyngby, Denmark.
Environ Sci Technol. 2010 Jan 1;44(1):24-33. doi: 10.1021/es9018207.
Microbially mediated terminal electron accepting processes (TEAPs) to a large extent control the fate of redox reactive elements and associated reactions in anoxic soils, sediments, and aquifers. This review focuses on thermodynamic controls and regulation of H2-dependent TEAPs, case studies illustrating this concept, and the quantitative description of thermodynamic controls in modeling. Other electron transfer processes are considered where appropriate. The work reviewed shows that thermodynamics and microbial kinetics are connected near thermodynamic equilibrium. Free energy thresholds for terminal respiration are physiologically based and often near -20 kJ mol(-1), depending on the mechanism of ATP generation; more positive free energy values have been reported under "starvation conditions" for methanogenesis and lower values for TEAPs that provide more energy. H2-dependent methanogenesis and sulfate reduction are under direct thermodynamic control in soils and sediments and generally approach theoretical minimum energy thresholds. If H2 concentrations are lowered by thermodynamically more potent TEAPs, these processes are inhibited. This principle is also valid for TEAPS providing more free energy, such as denitrification and arsenate reduction, but electron donor concentration cannot be lowered so that the processes reach theoretical energy thresholds. Thermodynamics and kinetics have been integrated by combining traditional descriptions of microbial kinetics with the equilibrium constant K and reaction quotient Q of a process, taking into account process-specific threshold energies. This approach is dynamically evolving toward a general concept of microbially driven electron transfer in anoxic environments and has been used successfully in applications ranging from bioreactor regulation to groundwater and sediment biogeochemistry.
微生物介导的末端电子接受过程（TEAPs）在很大程度上控制了还原态活性元素在缺氧土壤、沉积物和含水层中的命运和相关反应。本综述重点介绍了 H2 依赖性 TEAP 的热力学控制和调节，说明了这一概念的案例研究，以及在模型中定量描述热力学控制的方法。在适当的情况下，还考虑了其他电子转移过程。回顾的工作表明，热力学和微生物动力学在热力学平衡附近是相互关联的。末端呼吸的自由能阈值是基于生理学的，通常接近-20 kJ mol(-1)，这取决于 ATP 生成的机制；在产甲烷和 TEAP 的“饥饿条件”下，已经报道了更积极的自由能值，这些 TEAP 提供了更多的能量。在土壤和沉积物中，H2 依赖性的产甲烷作用和硫酸盐还原作用受直接热力学控制，通常接近理论最小能量阈值。如果 H2 浓度被热力学上更有力的 TEAP 降低，这些过程就会受到抑制。这一原理对于提供更多自由能的 TEAPs（如反硝化和砷酸盐还原）也是有效的，但不能降低电子供体浓度，以使这些过程达到理论能量阈值。通过将微生物动力学的传统描述与过程的平衡常数 K 和反应商 Q 相结合，并考虑到特定过程的阈值能量，将热力学和动力学结合起来。这种方法正在朝着缺氧环境中微生物驱动的电子转移的一般概念发展，并已成功应用于从生物反应器调节到地下水和沉积物生物地球化学的各种应用中。
