Bing Ryan G, Ford Kathryne C, Willard Daniel J, Manesh Mohamad J H, Straub Christopher T, Laemthong Tunyaboon, Alexander Benjamin H, Tanwee Tania, O'Quinn Hailey C, Poole Farris L, Vailionis Jason, Zhang Ying, Rodionov Dmitry, Adams Michael W W, Kelly Robert M
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA.
Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA, USA.
Metab Eng. 2024 Nov;86:99-114. doi: 10.1016/j.ymben.2024.09.007. Epub 2024 Sep 19.
The anaerobic bacterium Anaerocellum (f. Caldicellulosiruptor) bescii natively ferments the carbohydrate content of plant biomass (including microcrystalline cellulose) into predominantly acetate, H, and CO, and smaller amounts of lactate, alanine and valine. While this extreme thermophile (growth T 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.
厌氧细菌厌氧纤维素菌（隶属于嗜热纤维梭菌属）天然地将植物生物质（包括微晶纤维素）中的碳水化合物发酵，主要生成乙酸盐、氢气和二氧化碳，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78°C）天然不产乙醇，但此前已通过代谢工程使其具备了这种特性，不过最初乙醇产量较低（约15 mM）。在此，我们报告了在提高贝氏厌氧纤维素菌产乙醇能力方面取得的重大进展，目前乙醇产量已达到130 mM以上，同时通过尽量减少乙酸盐的形成提高了选择性。代谢工程的进展得益于改进的分子遗传工具以及对贝氏厌氧纤维素菌生长生理学的更好理解。对辅酶需求进行改造的突变嗜热醇脱氢酶（AdhE）的异源表达，以及与pH控制相关的生物反应器操作策略，是提高乙醇产量和发酵产物特异性的关键。从贝氏厌氧纤维素菌的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。
