Microbiology, Institute of Biological Sciences, University of Rostock, Albert-Einstein Str. 3, D-18059, Rostock, Germany.
Microbiology, Institute of Biological Sciences, University of Rostock, Albert-Einstein Str. 3, D-18059, Rostock, Germany.
J Biotechnol. 2019 Dec 20;306:105-117. doi: 10.1016/j.jbiotec.2019.09.005. Epub 2019 Sep 18.
The development of a bio-refinery industry based on liquid fuels is presumably key to successful replacement of fossil fuels and a reduction of carbon dioxide (CO) emissions. Ethanol and longer-chain alcohols are supposed to play a key role since they are relatively easy to produce, using microorganisms as whole-cell biocatalysts. Alcohols may be produced from lignocellulose-derived biomass or from synthesis gas (hydrogen, H; CO, carbon monoxide, CO). In anaerobes, common pathways involve the reduction of the intermediate acetyl-CoA with NAD(P)H by aldehyde (ALDH) and alcohol dehydrogenases (ADH). Alternatively, alcohols may be produced by the direct reduction of externally added or intermediately produced organic acids with reduced ferredoxin (Fd). The key enzyme catalyzing this thermodynamically difficult reaction is aldehyde:ferredoxin oxidoreductase (AOR), an oxygen sensitive protein present in some anaerobic bacteria and archaea. Here, we present increasing evidence for the importance of the AOR-ADH pathway in alcohol producing anaerobes. AOR heavily depends on compounds with a low redox potential, and reactions potentially coupled to the pathway are discussed. The putative ancient AOR-ADH pathway may be relatively widespread among anaerobes, and it may play an important role in a sustainable bioenergy concept via the reduction of organic acids to their corresponding alcohols.
基于液体燃料的生物精炼工业的发展大概是成功替代化石燃料和减少二氧化碳（CO）排放的关键。乙醇和长链醇应该发挥关键作用，因为它们相对容易生产，使用微生物作为全细胞生物催化剂。醇可以从木质纤维素衍生的生物质或合成气（氢气，H；一氧化碳，CO）中生产。在厌氧菌中，常见的途径包括用 NAD(P)H 还原中间产物乙酰辅酶 A 通过醛（ALDH）和醇脱氢酶（ADH）。或者，醇可以通过用还原型铁氧还蛋白（Fd）直接还原外加的或中间产生的有机酸来生产。催化这个热力学困难反应的关键酶是醛：铁氧还蛋白氧化还原酶（AOR），它是一些厌氧菌和古菌中存在的一种对氧气敏感的蛋白质。在这里，我们提出了越来越多的证据表明 AOR-ADH 途径在产醇厌氧菌中的重要性。AOR 严重依赖于具有低氧化还原电位的化合物，并且讨论了可能与该途径偶联的反应。假定的古老 AOR-ADH 途径可能在厌氧菌中相对普遍，并且通过将有机酸还原为相应的醇，它可能在可持续生物能源概念中发挥重要作用。
