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Recently, the research group led by Prof. Zhao Guang from the State Key Laboratory of Microbial Technology has made important progress on the construction of Escherichia coli cell factory with improved carbon atomic economy. The related work titled “Using a synthetic machinery to improve carbon yield with acetylphosphate as the core” was published in the journal Nature Communications.
Bioproduction of desired chemicals and materials is gaining momentum due to their environmentally friendliness and practical feasibility. In microorganisms, acetyl coenzyme A (acetyl-CoA) is not only a fundamental metabolite in central metabolic pathways, but also a precursor for numerous industrially relevant products. However, natural microorganisms, including E. coli and yeast widely used in bioproduction, usually convert glucose into acetyl-CoA through the glycolysis pathway together with pyruvate decarboxylation, in which 2 mol of CO2 are generated from each mol of glucose. This release of CO2 causes a significant decrease in the atomic economy of the targeted chemical biosynthetic pathway, representing the major carbon loss of microbial carbon metabolism and biorefining. To resolve this problem, this work developed E. coli cell factory with improved carbon atomic economy and sufficient supply of acetyl-CoA.
Figure. Development and application of E. coli cell factory with high carbon atomic economy
Acetylphosphate can be converted into acetyl-CoA under catalysis of transacetylase. This study focused on reprogramming of the central metabolism network of E. coli with acetylphosphate as the core, through the design of a static pathway reconstruction module and a dynamic metabolic flux allocation module. The static pathway reconstruction includes the design and optimization of the shortest artificial carbon conserving pathway in E. coli, the Sedeheptulose-1,7-bisphosphate Cycle with Trifunctional PhosphoKetolase (SCTPK). This cycle bypasses the carbon release in the pyruvate decarboxylation reaction, and converts glucose into the stoichiometric amounts of acetylphosphate. Moreover, this pathway only requires two heterogenous enzymes, lowering the protein expression burden and representing both carbon atomic economy and protein economy. To achieve the dynamic and rational allocation of metabolic flux, we developed a series of genetic circuits activated or repressed by acetylphosphate with various thresholds and dynamic ranges. Then, we integrated the SCTPK and genetic circuits to construct gene-metabolic oscillation systems with acetylphosphate as the core, enabling the maintenance of intracellular acetylphosphate homeostasis, avoiding the excessive acetylation of proteins caused by the accumulation of acetylphosphate, and promoting the dynamic and rational allocation of cellular resources between cell growth and bioproduction of the target chemical. Finally, this synthetic machinery was applied to the synthesis of several industrially relevant products. For example, mevalonate was produced with a yield of 0.61 g/g glucose, exceeding its native theoretical yield, and 73.42 g/L 3-hydroxypropionate was accumulated in fed-batch fermentation, representing the highest 3-hydroxypropionate production via malonyl-CoA pathway. This study provides a promising strategy for improving the carbon yield of microbial cell factories.
Prof. Zhao Guang is the corresponding author of the paper, and PhD student Guo Likun and Research Associate Professor Liu Min were co-first authors. Prof. Qi Qingsheng from Shandong University and Prof. Xian Mo from Qingdao Institute of Bioenergy and Bioprocess Technology also participated in this work. This work was financially supported by the National Key R&D Program, NSFC, and Foundation for Innovative Research Groups of State Key Laboratory of Microbial Technology.