Improving bioconversion of eugenol to coniferyl alcohol by constitutive promoters in Escherichia coli

Simple phenylpropanoids: recent advances in biological activities, biosynthetic pathways, and microbial production

Covering: 2000 to 2023Simple phenylpropanoids are a large group of natural products with primary C6-C3 skeletons. They are not only important biomolecules for plant growth but also crucial chemicals for high-value industries, including fragrances, nutraceuticals, biomaterials, and pharmaceuticals. However, with the growing global demand for simple phenylpropanoids, direct plant extraction or chemical synthesis often struggles to meet current needs in terms of yield, titre, cost, and environmental impact. Benefiting from the rapid development of metabolic engineering and synthetic biology, microbial production of natural products from inexpensive and renewable sources provides a feasible solution for sustainable supply. This review outlines the biological activities of simple phenylpropanoids, compares their biosynthetic pathways in different species (plants, bacteria, and fungi), and summarises key research on the microbial production of simple phenylpropanoids over the last decade, with a focus on engineering strategies that seem to hold most potential for further development. Moreover, constructive solutions to the current challenges and future perspectives for industrial production of phenylpropanoids are presented.

Challenges and opportunities for engineered Escherichia coli as a pivotal chassis toward versatile tyrosine-derived chemicals production

Growing concerns over limited fossil resources and associated environmental problems are motivating the development of sustainable processes for the production of high-volume fuels and high-value-added compounds. The shikimate pathway, an imperative pathway in most microorganisms, is branched with tyrosine as the rate-limiting step precursor of valuable aromatic substances. Such occurrence suggests the shikimate pathway as a promising route in developing microbial cell factories with multiple applications in the nutraceutical, pharmaceutical, and chemical industries. Therefore, an increasing number of studies have focused on this pathway to enable the biotechnological manufacture of pivotal and versatile aromatic products. With advances in genome databases and synthetic biology tools, genetically programmed Escherichia coli strains are gaining immense interest in the sustainable synthesis of chemicals. Engineered E. coli is expected to be the next bio-successor of fossil fuels and plants in commercial aromatics synthesis. This review summarizes successful and applicable genetic and metabolic engineering strategies to generate new chassis and engineer the iterative pathway of the tyrosine route in E. coli, thus addressing the opportunities and current challenges toward the realization of sustainable tyrosine-derived aromatics.

Production of hydroxytyrosol through whole-cell bioconversion from L-DOPA using engineered Escherichia coli

Hydroxytyrosol (HT), a polyphenolic molecule of high value, is used in the nutraceutical, cosmetic, food, and livestock nutrition industries. As a natural product, HT is chemically manufactured or extracted from olives; nevertheless, the increasing demand mandates the exploration and development of alternative sources, such as heterologous production by recombinant bacteria. In order to achieve this purpose, we have molecularly modified Escherichia coli to carry two plasmids. For conversion of L-DOPA (Levodopa) into HT efficiently, it is necessary to enhance the expression of DODC (DOPA decarboxylase), ADH (alcohol dehydrogenases), MAO (Monoamine oxidase) and GDH (glucose dehydrogenases). The step that significantly affects the rate of ht biosynthesis is likely to be associated with the reaction facilitated by DODC enzymatic activity, as suggested by the result of in vitro catalytic experiment and HPLC. Then Pseudomonas putida, Sus scrofa, Homo sapiens and Levilactobacillus brevis DODC were taken into comparsion. The DODC from H. sapiens is superior to that of P. putida, S. scrofa or L. brevis for HT production. Seven promoters were introduced to increase the expression levels of catalase (CAT) to remove the byproduct H₂O₂ and optimized coexpression strains were obtained after screening. After the 10-hour operation, the optimized whole-cell biocatalyst produced HT at a maximum titer of 4.84 g/L with over 77.5% molar substrate conversion rate.

An artificial pathway for trans-4-hydroxy-L-pipecolic acid production from L-lysine in Escherichia coli

Trans-4-hydroxy-L-pipecolic acid (Trans-4-HyPip) is a hydroxylated product of L-pipecolic acid, and which is widely used in pharmaceutical and chemical industry. Here, a trans-4-HyPip biosynthesis module was designed and constructed in Escherichia coli by overexpressing lysine α-oxidase, Δ1-piperideine-2-carboxylase reductase, glucose dehydrogenase, lysine permease, catalase and L-pipecolic acid trans-4-hydroxylase for expanding the lysine catabolism pathway. 4.89 g/L of trans-4-HyPip was generated in shake flasks from 8 g/L of L-pipecolic acid. By this approach, 14.86 g/L of trans-4-HyPip was produced from lysine after 48 h in a 5-L bioreactor. As far as we know, this is the first multi-enzyme cascade catalytic system for the production of trans-4-HyPip using Escherichia coli from L-lysine. Therefore, it can be considered as a potential candidate for industrial production of trans-4-HyPip in microorganisms.

An Artificial Pathway for N-Hydroxy-Pipecolic Acid Production From L-Lysine in Escherichia coli

N-hydroxy-pipecolic acid (NHP) is a hydroxylated product of pipecolic acid and an important systemic acquired resistance signal molecule. However, the biosynthesis of NHP does not have a natural metabolic pathway in microorganisms. Here, we designed and constructed a promising artificial pathway in Escherichia coli for the first time to produce NHP from biomass-derived lysine. This biosynthesis route expands the lysine catabolism pathway and employs six enzymes to sequentially convert lysine into NHP. This artificial route involves six functional enzyme coexpression: lysine α-oxidase from Scomber japonicus (RaiP), glucose dehydrogenase from Bacillus subtilis (GDH), Δ1-piperideine-2-carboxylase reductase from Pseudomonas putida (DpkA), lysine permease from E. coli (LysP), flavin-dependent monooxygenase (FMO1), and catalase from E. coli (KatE). Moreover, different FMO1s are used to evaluate the performance of the produce NHP. A titer of 111.06 mg/L of NHP was yielded in shake flasks with minimal medium containing 4 g/L of lysine. By this approach, NHP has so far been produced at final titers reaching 326.42 mg/L by 48 h in a 5-L bioreactor. To the best of our knowledge, this is the first NHP process using E. coli and the first process to directly synthesize NHP by microorganisms. This study lays the foundation for the development and utilization of renewable resources to produce NHP in microorganisms.