α-Santalene belongs to a class of natural compounds with many physiological functions and medical applications. Advances in metabolic engineering enable non-native hosts (e.g., Escherichia coli) to produce α-santalene, the precursor of sandalwood oil. However, imbalances in enzymatic activity often result in a metabolic burden on hosts and repress the synthetic capacity of the desired product. In this work, we manipulated ribosome binding sites (RBSs) to optimize an α-santalene synthetic operon in E. coli, and the best engineered E. coli NA-IS 3D strain could produce α-santalene at a titer of 412 mg•L −1 . Concerning the observation of the inverse correlation between indole synthesis and α-santalene production, this study speculated that indoleassociated amino acid metabolism would be competitive to the synthesis of α-santalene rather than indole toxicity itself. The deletion of tnaA could lead to a 1.5-fold increase in α-santalene production to a titer of 599 mg•L −1 in E. coli tnaA − NA-IS 3D . Our results suggested that the optimization of RBS sets of the synthetic module and attenuation of the competitive pathway are promising approaches for improving the production of terpenoids including α-santalene.
Mevalonate is an important platform compound for the biosynthesis of isoprenoids.It can be synthesized from acetyl-CoA in the presence of nicotinamide adenine dinucleotide phosphate (NADPH) by the introduced mvaES operon in Escherichia coli.The influences of E. coli hosts, acetyl-CoA supply, and NADPH availability were assessed and engineered to improve the production titer and yield of mevalonate from glycerol. As a result, E. coli DH5α was found to be the best host with high specific capability and titer of mevalonate from glycerol. Through the engineering of phosphoketolase-phosphotransacetylase (xPK-PTA) bypass and NADPH availability, a final titer of 7.21 g/L with a specific capability of 1.36 g/g dry cell weight was gained in flask culture. Our work could offer new information to metabolically engineer the mevalonate pathway for the efficient production of isoprenoids.
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