Linking thermodynamics and kinetics to assess pathway reversibility in anaerobic bioprocesses
Linking thermodynamics and kinetics to assess pathway reversibility in anaerobic bioprocesses
复制标题
DOI：
10.1039/c3ee42754d
复制
发表时间：
2013-12-01
影响因子：
32.5
通讯作者：
Kleerebezem, Robbert
中科院分区：
文献类型：
--
作者：
Gonzalez-Cabaleiro, Rebeca;Lema, Juan M.;Kleerebezem, Robbert
正在进行的可持续燃料生产研究需要改进所涉及的微生物催化剂。特定厌氧分解代谢反应可能的可逆性为新型还原生物过程的发展开辟了一系列可能性。这些还原生物氢化途径能够生产高能量密度的化学物质作为生物燃料，例如醇和长链脂肪酸。由于缺乏氧气等强电子受体，厌氧生物过程发生在能量稀缺的条件下，并为这些能量密集（还原）化学物质提供代谢途径。代谢反应的发生非常接近热力学平衡，能量耗散最小，因此，产物和底物浓度的环境变化可以很容易地逆转所催化的化学反应的驱动力。这项工作的目的是研究感兴趣的特定厌氧途径的潜在可逆性。分析生化途径中不同步骤的热力学，并与有关动力学和生理约束的假设相结合，以评估通过施加过程条件的变化，途径是否可能可逆。结果表明，（i）在同型乙酸生成中，根据系统中的氢分压，它们可能在还原和氧化方向上进行操作，（ii）用氢将乙酸盐还原为丁酸盐是不可行的，但用乙醇或乳酸盐作为电子供体从乙酸盐生产丁酸盐中不存在明显的生化瓶颈，（iii）用乙醇作为电子供体将短链脂肪酸还原为长链脂肪酸在热力学和动力学上似乎是可行的，以及（iv）从相应的脂肪酸（例如乙醇）生产醇研究发现，在生化途径中的特定位点需要质子易位，以补偿乙酸盐磷酸化所需的 ATP 并实现能量收集。总的来说，这里提出的方法允许分析分解代谢途径的潜在可逆性，从而有助于开发用于生产生物燃料和化学品的高效可靠的厌氧生物过程。
The on-going research towards sustainable fuel production entails the improvement of the microbial catalysts involved. The possible reversibility of specific anaerobic catabolic reactions opens up a range of possibilities for the development of novel reductive bioprocesses. These reductive biohydrogenation pathways enable production of high energy density chemicals of interest as biofuels such as alcohols and long chain fatty acids. Anaerobic bioprocesses take place under energy scarcity conditions due to the absence of strong electron acceptors such as oxygen, and provide metabolic pathways towards these energy dense (reduced) chemicals. Metabolic reactions take place very close to thermodynamic equilibrium with minimum energy dissipation and consequently, environmental changes in product and substrate concentrations can easily reverse the driving force of the chemical reaction catalysed. The objective of this work is to investigate the potential reversibility of specific anaerobic pathways of interest. The thermodynamics of the different steps in biochemical pathways are analysed and combined with assumptions concerning kinetic and physiological constraints to evaluate if pathways are potentially reversible by imposing changes in process conditions. The results suggest that (i) in homoacetogenesis they may operate in both reductive and oxidative directions depending on the hydrogen partial pressure in the system, (ii) acetate reduction to butyrate with hydrogen is not feasible, but no biochemical bottlenecks are apparent in butyrate production from acetate with ethanol or lactate as electron donors, (iii) the reduction of short chain to longer chain fatty acids with ethanol as the electron donor appears thermodynamically and kinetically feasible, and (iv) alcohol production from the corresponding fatty acids (e. g. ethanol from acetate) was found to require proton translocations at specific sites in the biochemical pathways in order to compensate for the ATP required for phosphatation of acetate and to enable energy harvesting. Overall, the methodology proposed here allows for analysing the potential reversibility of catabolic pathways and therewith contributes to the development of efficient and reliable anaerobic bioprocesses for the production of biofuels and chemicals.