Ethylene glycol is a promising substrate for bioprocesses which can be derived from widely abundant CO2 or plastic waste. In this work, we describe the construction of an eight-step synthetic metabolic pathway enabling carbon-conserving biosynthesis of threonine from ethylene glycol. This route extends the previously disclosed synthetic threose-dependent glycolaldehyde assimilation (STEGA) pathway for the synthesis of 2-oxo-4-hydroxybutyrate with three additional reaction steps catalyzed by homoserine transaminase, homoserine kinase, and threonine synthase. We first validated the functionality of the new pathway in an Escherichia coli strain auxotrophic for threonine, which was also employed for discovering a better-performing D-threose dehydrogenase enzyme activity. Subsequently, we transferred the pathway to producer strains and used 13C-tracer experiments to improve threonine biosynthesis starting from glycolaldehyde. Finally, extending the pathway for ethylene glycol assimilation resulted in the production of up to 6.5 mM (or 0.8 g L−1) threonine by optimized E. coli strains at a yield of 0.10 mol mol−1 (corresponding to 20 % of the theoretical yield).

中文翻译：

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构建乙二醇生物合成苏氨酸的合成代谢途径


乙二醇是一种很有前途的生物工艺底物，可以从广泛丰富的 CO2 或塑料废物中获得。在这项工作中，我们描述了八步合成代谢途径的构建，能够从乙二醇中保碳生物合成苏氨酸。该路线扩展了先前报道的合成苏糖依赖性乙醛同化 （STEGA） 途径，用于合成 2-氧代-4-羟基丁酸酯，具有由高丝氨酸转氨酶、高丝氨酸激酶和苏氨酸合酶催化的三个额外反应步骤。我们首先在苏氨酸营养缺陷型大肠杆菌菌株中验证了新途径的功能，该菌株也用于发现性能更好的 D-苏糖脱氢酶活性。随后，我们将途径转移到生产菌株，并使用 13 C 示踪剂实验来改善从乙醛开始的苏氨酸生物合成。最后，扩展乙二醇同化途径导致优化的大肠杆菌菌株以 0.10 mol mol-1 的产量（相当于理论产量的 20%）产生高达 6.5 mM（或 0.8 g L-1）的苏氨酸。