The anaerobic bacterium Anaerocellum (f. Caldicellulosiruptor) bescii natively ferments the carbohydrate content of plant biomass (including microcrystalline cellulose) into predominantly acetate, H2, and CO2, and smaller amounts of lactate, alanine and valine. While this extreme thermophile (growth Topt 78 °C) is not natively ethanologenic, it has been previously metabolically engineered with this property, albeit initially yielding low solvent titers (∼15 mM). Herein we report significant progress on improving ethanologenicity in A. bescii, such that titers above 130 mM have now been achieved, while concomitantly improving selectivity by minimizing acetate formation. Metabolic engineering progress has benefited from improved molecular genetic tools and better understanding of A. bescii growth physiology. Heterologous expression of a mutated thermophilic alcohol dehydrogenase (AdhE) modified for co-factor requirement, coupled with bioreactor operation strategies related to pH control, have been key to enhanced ethanol generation and fermentation product specificity. Insights gained from metabolic modeling of A. bescii set the stage for its further improvement as a metabolic engineering platform.

中文翻译：

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将乙醇产入极端嗜热细菌 Anaerocellum (f. Caldicellulosiriuptor) bescii


厌氧细菌 Anaerocellum (f. Caldicellulosiruptor) bescii 将植物生物质（包括微晶纤维素）中的碳水化合物天然发酵成主要是乙酸盐、H2 和 CO2，以及少量的乳酸、丙氨酸和缬氨酸。虽然这种极端嗜热菌（生长温度为 Topt 78 °C）本身不产乙醇，但之前已对其进行了具有此特性的代谢改造，尽管最初产生了低溶剂滴度（∼15 mM）。在此，我们报告了在改善 A. bescii 的乙醇产率方面取得的重大进展，目前滴度已达到 130 mM 以上，同时通过最大限度地减少乙酸盐的形成来提高选择性。代谢工程的进步得益于分子遗传工具的改进和对 A. bescii 生长生理学的更好理解。针对辅因子需求进行修饰的突变嗜热乙醇脱氢酶 (AdhE) 的异源表达，加上与 pH 控制相关的生物反应器操作策略，是增强乙醇生成和发酵产物特异性的关键。从 A. bescii 代谢模型中获得的见解为其作为代谢工程平台的进一步改进奠定了基础。