Development of efficient microbial cell factory for whole-cell bioconversion of L-threonine to 2-hydroxybutyric acid

Recent advances on engineering Escherichia coli and Corynebacterium glutamicum for efficient production of L-threonine and its derivatives

L-threonine, one of the three major amino acids, plays a vital role in various industries such as food, feed, pharmaceuticals, and cosmetics. Currently, the fermentation-based production of L-threonine has evolved into an efficient, cost-effective, and environmentally friendly industrial process. Escherichia coli and Corynebacterium glutamicum, as the industrial workhorses of amino acids production, have long been widely studied due to their well-established genetic backgrounds and powerful molecular tools. This review focuses on recent advances in the microbial production of L-threonine by metabolic engineering. From three key modules, including L-threonine synthesis module, central metabolism module and global regulation module, we provide a comprehensive analysis on the entire metabolic pathway of L-threonine and the global regulation of the production process. Furthermore, we systematically summarize biotransformation methods for producing high-value derivatives of L-threonine, thereby broadening the application scope and market potential of L-threonine. Overall, this review shows many effective strategies for the biosynthesis of L-threonine, and offers guidance for the microbial production of L-aspartate family amino acids and their derivatives.

Metabolic Engineering of Escherichia coli for De Novo Production of 1,2-Butanediol

1,2-Butanediol (1,2-BDO) is an important platform chemical widely utilized in the synthesis of polyester polyols, plasticizers, cosmetics, and pharmaceuticals. However, no natural metabolic pathway for its biosynthesis has been identified, and biological production of 1,2-BDO from renewable bioresources has not been reported so far. In this study, we designed and experimentally verified a feasible non-natural synthesis pathway for the de novo production of 1,2-BDO from renewable carbohydrates for the first time. This pathway extends the l-threonine synthesis pathway by introducing two artificial metabolic modules to sequentially convert l-threonine into 2-hydroxybutyric acid and 1,2-BDO. Following key enzyme screening and enhancement of l-threonine synthesis module in the chassis microorganism, the best engineered Escherichia coli strain was able to produce 0.15 g/L 1,2-BDO using glucose as the sole carbon source. This work lays the foundation for the bioproduction of 1,2-BDO from renewable resources.

Whole-Cell Display of Phosphotransferase in Escherichia coli for High-Efficiency Extracellular ATP Production

Adenosine triphosphate (ATP), as a universal energy currency, takes a central role in many biochemical reactions with potential for the synthesis of numerous high-value products. However, the high cost of ATP limits industrial ATP-dependent enzyme-catalyzed reactions. Here, we investigated the effect of cell-surface display of phosphotransferase on ATP regeneration in recombinant Escherichia coli. By N-terminal fusion of the super-folder green fluorescent protein (sfGFP), we successfully displayed the phosphotransferase of Pseudomonas brassicacearum (PAP-Pb) on the surface of E. coli cells. The catalytic activity of sfGFP-PAP-Pb intact cells was 2.12 and 1.47 times higher than that of PAP-Pb intact cells, when the substrate was AMP and ADP, respectively. The conversion of ATP from AMP or ADP were up to 97.5% and 80.1% respectively when catalyzed by the surface-displayed enzyme at 37 °C for only 20 min. The whole-cell catalyst was very stable, and the enzyme activity of the whole cell was maintained above 40% after 40 rounds of recovery. Under this condition, 49.01 mg/mL (96.66 mM) ATP was accumulated for multi-rounds reaction. This ATP regeneration system has the characteristics of low cost, long lifetime, flexible compatibility, and great robustness.