Metabolic engineering of microorganisms for the synthesis of plant natural products

Microbial synthesis of anthocyanins and pyranoanthocyanins: current bottlenecks and potential solutions

Anthocyanins (ACNs) are secondary metabolites found in plants. Due to their impressive biological activities, ACNs have gained significant popularity and extensive application within the food, pharmaceutical, and nutraceutical industries. A derivative of ACNs: pyranoanthocyanins (PACNs) possesses more stable properties and interesting biological activities. However, conventional methods for the production of ACNs, including chemical synthesis and plant extraction, involve organic solvents. Microbial synthesis of ACNs from renewable biomass, such as amino acids or flavonoids, is considered a sustainable and environmentally friendly method for large-scale production of ACNs. Recently, the construction of microbial cell factories (MCFs) for the efficient biosynthesis of ACNs and PACNs has attracted much attention. In this review, we summarize the cases of microbial synthesis of ACNs, and analyze the bottlenecks in reconstructing the metabolic pathways for synthesizing PACNs in microorganisms. Consequently, there is an urgent need to investigate the mechanisms behind the development of MCFs for PACNs synthesis. Such research also holds significant promise for advancing the production of food pigments. Meanwhile, we propose potential solutions to the bottleneck problem based on metabolic engineering and enzyme engineering. Finally, the development prospects of natural food and biotechnology are discussed.

Improving the substrate binding of acetyl-CoA carboxylase (AccB) from Streptomyces antibioticus through computational enzyme engineering

Malonyl-CoA serves as the main building block for the biosynthesis of many important polyketides, as well as fatty acid-derived compounds, such as biofuel. Escherichia coli, Corynebacterium gultamicum, and Saccharomyces cerevisiae have recently been engineered for the biosynthesis of such compounds. However, the developed processes and strains often have insufficient productivity. In the current study, we used enzyme-engineering approach to improve the binding of acetyl-CoA with ACC. We generated different mutations, and the impact was calculated, which reported that three mutations, that is, S343A, T347W, and S350W, significantly improve the substrate binding. Molecular docking investigation revealed an altered binding network compared to the wild type. In mutants, additional interactions stabilize the binding of the inner tail of acetyl-CoA. Using molecular simulation, the stability, compactness, hydrogen bonding, and protein motions were estimated, revealing different dynamic properties owned by the mutants only but not by the wild type. The findings were further validated by using the binding-free energy (BFE) method, which revealed these mutations as favorable substitutions. The total BFE was reported to be -52.66 ± 0.11 kcal/mol for the wild type, -55.87 ± 0.16 kcal/mol for the S343A mutant, -60.52 ± 0.25 kcal/mol for T347W mutant, and -59.64 ± 0.25 kcal/mol for the S350W mutant. This shows that the binding of the substrate is increased due to the induced mutations and strongly corroborates with the docking results. In sum, this study provides information regarding the essential hotspot residues for the substrate binding and can be used for application in industrial processes.

Two-Phase Fermentation Systems for Microbial Production of Plant-Derived Terpenes

Microbial cell factories, renowned for their economic and environmental benefits, have emerged as a key trend in academic and industrial areas, particularly in the fermentation of natural compounds. Among these, plant-derived terpenes stand out as a significant class of bioactive natural products. The large-scale production of such terpenes, exemplified by artemisinic acid-a crucial precursor to artemisinin-is now feasible through microbial cell factories. In the fermentation of terpenes, two-phase fermentation technology has been widely applied due to its unique advantages. It facilitates in situ product extraction or adsorption, effectively mitigating the detrimental impact of product accumulation on microbial cells, thereby significantly bolstering the efficiency of microbial production of plant-derived terpenes. This paper reviews the latest developments in two-phase fermentation system applications, focusing on microbial fermentation of plant-derived terpenes. It also discusses the mechanisms influencing microbial biosynthesis of terpenes. Moreover, we introduce some new two-phase fermentation techniques, currently unexplored in terpene fermentation, with the aim of providing more thoughts and explorations on the future applications of two-phase fermentation technology. Lastly, we discuss several challenges in the industrial application of two-phase fermentation systems, especially in downstream processing.

Recent Developments and Applications of Biocatalytic and Chemoenzymatic Synthesis for the Generation of Diverse Classes of Drugs

Biocatalytic and chemoenzymatic biosynthesis are powerful methods of organic chemistry that use enzymes to execute selective reactions and allow the efficient production of organic compounds. The advantages of these approaches include high selectivity, mild reaction conditions, and the ability to work with complex substrates. The utilization of chemoenzymatic techniques for the synthesis of complicated compounds has lately increased dramatically in the area of organic chemistry. Biocatalytic technologies and modern synthetic methods are utilized synergistically in a multi-step approach to a target molecule under this paradigm. Chemoenzymatic techniques are promising for simplifying access to essential bioactive compounds because of the remarkable regio- and stereoselectivity of enzymatic transformations and the reaction diversity of modern organic chemistry. Enzyme kits may include ready-to-use, reproducible biocatalysts. Its use opens up new avenues for the synthesis of active therapeutic compounds and aids in drug development by synthesizing active components to construct scaffolds in a targeted and preparative manner. This study summarizes current breakthroughs as well as notable instances of biocatalytic and chemoenzymatic synthesis. To assist organic chemists in the use of enzymes for synthetic applications, it also provides some basic guidelines for selecting the most appropriate enzyme for a targeted reaction while keeping aspects like cofactor requirement, solvent tolerance, use of whole cell or isolated enzymes, and commercial availability in mind.

Microbial synthesis of the plant natural product precursor p-coumaric acid with Corynebacterium glutamicum

BACKGROUND

Phenylpropanoids such as p-coumaric acid represent important precursors for the synthesis of a broad range of plant secondary metabolites including stilbenoids, flavonoids, and lignans, which are of pharmacological interest due to their health-promoting properties. Although extraction from plant material or chemical synthesis is possible, microbial synthesis of p-coumaric acid from glucose has the advantage of being less expensive and more resource efficient. In this study, Corynebacterium glutamicum was engineered for the production of the plant polyphenol precursor p-coumaric acid from glucose.

RESULTS

Heterologous expression of the tyrosine ammonia-lyase encoding gene from Flavobacterium johnsoniae enabled the conversion of endogenously provided tyrosine to p-coumaric acid. Product consumption was avoided by abolishing essential reactions of the phenylpropanoid degradation pathway. Accumulation of anthranilate as a major byproduct was eliminated by reducing the activity of anthranilate synthase through targeted mutagenesis to avoid tryptophan auxotrophy. Subsequently, the carbon flux into the shikimate pathway was increased, phenylalanine biosynthesis was reduced, and phosphoenolpyruvate availability was improved to boost p-coumaric acid accumulation. A maximum titer of 661 mg/L p-coumaric acid (4 mM) in defined mineral medium was reached. Finally, the production strain was utilized in co-cultivations with a C. glutamicum strain previously engineered for the conversion of p-coumaric acid into the polyphenol resveratrol. These co-cultivations enabled the synthesis of 31.2 mg/L (0.14 mM) resveratrol from glucose without any p-coumaric acid supplementation.

CONCLUSIONS

The utilization of a heterologous tyrosine ammonia-lyase in combination with optimization of the shikimate pathway enabled the efficient production of p-coumaric acid with C. glutamicum. Reducing the carbon flux into the phenylalanine and tryptophan branches was the key to success along with the introduction of feedback-resistant enzyme variants.

Membrane manipulation by free fatty acids improves microbial plant polyphenol synthesis

Microbial synthesis of nutraceutically and pharmaceutically interesting plant polyphenols represents a more environmentally friendly alternative to chemical synthesis or plant extraction. However, most polyphenols are cytotoxic for microorganisms as they are believed to negatively affect cell integrity and transport processes. To increase the production performance of engineered cell factories, strategies have to be developed to mitigate these detrimental effects. Here, we examine the accumulation of the stilbenoid resveratrol in the cell membrane and cell wall during its production using Corynebacterium glutamicum and uncover the membrane rigidifying effect of this stilbenoid experimentally and with molecular dynamics simulations. A screen of free fatty acid supplements identifies palmitelaidic acid and linoleic acid as suitable additives to attenuate resveratrol's cytotoxic effects resulting in a three-fold higher product titer. This cost-effective approach to counteract membrane-damaging effects of product accumulation is transferable to the microbial production of other polyphenols and may represent an engineering target for other membrane-active bioproducts.

Aromatic natural products synthesis from aromatic lignin monomers using Acinetobacter baylyi ADP1

Achieving sustainable chemical synthesis and a circular economy will require process innovation to minimize or recover existing waste streams. Valorization of lignin biomass has the ability to advance this goal. While lignin has proved a recalcitrant feedstock for upgrading, biological approaches can leverage native microbial metabolism to simplify complex and heterogeneous feedstocks to tractable starting points for biochemical upgrading. Recently, we demonstrated that one microbe with lignin relevant metabolism, Acinetobacter baylyi ADP1, is both highly engineerable and capable of undergoing rapid design-build-test-learn cycles, making it an ideal candidate for these applications. Here, we utilize these genetic traits and ADP1's native β-ketoadipate metabolism to convert mock alkali pretreated liquor lignin (APL) to two valuable natural products, vanillin-glucoside and resveratrol. En route, we create strains with up to 22 genetic modifications, including up to 8 heterologously expressed enzymes. Our approach takes advantage of preexisting aromatic species in APL (vanillate, ferulate, and p-coumarate) to create shortened biochemical routes to end products. Together, this work demonstrates ADP1's potential as a platform for upgrading lignin waste streams and highlights the potential for biosynthetic methods to maximize the existing chemical potential of lignin aromatic monomers.

Application of Adaptive Laboratory Evolution in Lipid and Terpenoid Production in Yeast and Microalgae

Due to the complexity of metabolic and regulatory networks in microorganisms, it is difficult to obtain robust phenotypes through artificial rational design and genetic perturbation. Adaptive laboratory evolution (ALE) engineering plays an important role in the construction of stable microbial cell factories by simulating the natural evolution process and rapidly obtaining strains with stable traits through screening. This review summarizes the application of ALE technology in microbial breeding, describes the commonly used methods for ALE, and highlights the important applications of ALE technology in the production of lipids and terpenoids in yeast and microalgae. Overall, ALE technology provides a powerful tool for the construction of microbial cell factories, and it has been widely used in improving the level of target product synthesis, expanding the range of substrate utilization, and enhancing the tolerance of chassis cells. In addition, in order to improve the production of target compounds, ALE also employs environmental or nutritional stress strategies corresponding to the characteristics of different terpenoids, lipids, and strains.

A new sesquiterpene synthase catalyzing the formation of (R)-β-bisabolene from medicinal plant Colquhounia coccinea var. mollis and its anti-adipogenic and antibacterial activities

The sesquiterpene β-bisabolene possessing R and S configurations is commonly found in plant essential oils with antimicrobial and antioxidant activities. Here, we report the cloning and functional characterization of a (R)-β-bisabolene synthase gene (CcTPS2) from a Lamiaceae medicinal plant Colquhounia coccinea var. mollis. The biochemical function of CcTPS2 catalyzing the cyclization of farnesyl diphosphate to form a single product (R)-β-bisabolene was characterized through an engineered Escherichia coli producing diverse polyprenyl diphosphate precursors and in vitro enzyme assay, indicating that CcTPS2 was a high-fidelity (R)-β-bisabolene synthase. The production of (R)-β-bisabolene in an engineered E. coli strain harboring the exogenous mevalonate pathway, farnesyl diphosphate synthase and CcTPS1 genes was 17 mg/L under shaking flask conditions. Ultimately, 120 mg of purified (R)-β-bisabolene was obtained from the engineered E. coli, and its structure was elucidated by detailed spectroscopic analyses (including 1D and 2D NMR, and specific rotation). Four chimeric enzymes were constructed through domain swapping, which altered the product outcome, indicating the region important for substrate and product specificity. In addition, (R)-β-bisabolene exhibited anti-adipogenic activity in the model organism Caenorhabditis elegans and antibacterial activity selectively against Gram-positive bacteria.

The Laccase of Myrothecium roridum VKM F-3565: A New Look at Fungal Laccase Tolerance to Neutral and Alkaline Conditions

Most of the currently known fungal laccases show their maximum activity under acidic environmental conditions. It is known that a decrease in the activity of a typical laccase at neutral or alkaline pH values is the result of an increase in the binding of the hydroxide anion to the T2/T3 copper center, which prevents the transfer of an electron from the T1 Cu to the trinuclear copper center. However, evolutionary pressure has resolved the existing limitations in the catalytic mechanism of laccase, allowing such enzymes to be functionally active under neutral/alkaline pH conditions, thereby giving fungi an advantage for their survival. Combined molecular and biochemical studies, homological modeling, calculation of the electrostatic potential on the Connolly surface at pH 5.0 and 7.0, and structural analysis of the novel alkaliphilic laccase of Myrothecium roridum VKM F-3565 and alkaliphilic and acidophilic fungal laccases with a known structure allowed a new intramolecular channel near the one of the catalytic aspartate residues at T2-copper atom to be found. The amino acid residues of alkaliphilic laccases forming this channel can presumably serve as proton donors for catalytic aspartates under neutral conditions, thus ensuring proper functioning. For the first time for ascomycetous laccases, the production of new trimeric products of phenylpropanoid condensation under neutral conditions has been shown, which could have a potential for use in pharmacology.

Trichoderma species from plant and soil: An excellent resource for biosynthesis of terpenoids with versatile bioactivities

BACKGROUND

Trichoderma species are rich source of bioactive secondary metabolites. In the past decades, a series of secondary metabolites were reported from different Trichoderma fungi, among which terpenoids possessing versatile structural diversities and extensive pharmacological activities are one of the particularly important categories.

AIM OF REVIEW

The review aims to summarize the terpenoids isolated from Trichoderma species regarding their structural diversities, biological activities, and promising biosynthetic potentials.

KEY SCIENTIFIC CONCEPTS OF REVIEW

So far, a total of 253 terpenoids, including 202 sesquiterpenes, 48 diterpenes, 2 monoterpenes and 1 meroterpenoid, were isolated and identified from Trichoderma species between 1948 and 2022. Pharmacological investigations of Trichoderma terpenoids mainly focused on their antibacterial activities, antifungal activities, inhibitory activities on marine plankton species and cytotoxic activities, indicating that Trichoderma species are important microbial agents for drug discovery and environmentally friendly agrochemicals development. Intriguing chemistry and enzymology involved in the biosynthesis of Trichoderma terpenoids were also presented to facilitate further precise genome mining-guided novel structure discovery. Taken together, the abundance of novel skeletons, bioactivities and biosynthetic potentials presents new opportunities for drug and agrochemicals discovery, genome mining and enzymology exploration from Trichoderma species. The work will provide references for the profound study of terpenoids derived from Trichoderma, and facilitate further studies on Trichoderma species in the areas of chemistry, medicine, agriculture and microbiology.

Engineering phototrophic bacteria for the production of terpenoids

With more than 80 000 compounds, terpenoids represent one of the largest classes of secondary metabolites naturally produced by various plants and other organisms. Owing to the tremendous structural diversity, they offer a wide range of properties relevant for biotechnological and pharmaceutical applications. In this context, heterologous terpenoid production in engineered microbial hosts represents an often cost-effective and eco-friendly way to make these valuable compounds industrially available. This review provides an overview of current strategies to employ and engineer oxygenic and anoxygenic phototrophic bacteria as alternative cell factories for sustainable terpenoid production. Besides terpenoid pathway engineering, the effects of different illumination strategies on terpenoid photoproduction are key elements in the latest studies.

Recent Advances in Biocatalysis for Drug Synthesis

Biocatalysis is constantly providing novel options for the synthesis of active pharmaceutical ingredients (APIs). In addition to drug development and manufacturing, biocatalysis also plays a role in drug discovery and can support many active ingredient syntheses at an early stage to build up entire scaffolds in a targeted and preparative manner. Recent progress in recruiting new enzymes by genome mining and screening or adapting their substrate, as well as product scope, by protein engineering has made biocatalysts a competitive tool applied in academic and industrial spheres. This is especially true for the advances in the field of nonribosomal peptide synthesis and enzyme cascades that are expanding the capabilities for the discovery and synthesis of new bioactive compounds via biotransformation. Here we highlight some of the most recent developments to add to the portfolio of biocatalysis with special relevance for the synthesis and late-stage functionalization of APIs, in order to bypass pure chemical processes.

Biosynthesis and regulation of anthocyanin pathway genes

Anthocyanins are the phenolic compounds responsible for coloring pigments in fruits and vegetables. Anthocyanins offer a wide range of health benefits to human health. Their scope has expanded dramatically in the past decade, making anthocyanin control, influx, and outflow regulation fascinating for many researchers. The main culprit is anthocyanin stability and concentration form, which demands novel ways because these are critical in the food industry. This review aims to examine anthocyanin synthesis via triggering transcription genes that code for anthocyanin-producing enzymes. The balance between production and breakdown determines anthocyanin accumulation. Thus, increasing the anthocyanin content in food requires the stability of molecules in the vacuolar lumen, the pigment fading process, and a better understanding of the mechanism. The promising option is biosynthesis by metabolically engineered microorganisms with a lot of success. This study aims to look into and evaluate the existing literature on anthocyanin production, namely the biosynthesis of anthocyanin pathway genes, production by microbial cell factories, and the regulatory factors that can modulate the production of anthocyanins. Understanding these mechanisms will provide new biotechnological approaches.Key points• Factors affecting the regulation of anthocyanins• Focus on degradation, biosynthesis pathway genes, and alternative systems for the production of anthocyanins• Microbial cell factories can be used to produce large amounts of anthocyanins.

Expression of phenylalanine ammonia lyases in Synechocystis sp. PCC 6803 and subsequent improvements of sustainable production of phenylpropanoids

Background

Phenylpropanoids represent a diverse class of industrially important secondary metabolites, synthesized in plants from phenylalanine and tyrosine. Cyanobacteria have a great potential for sustainable production of phenylpropanoids directly from CO₂, due to their photosynthetic lifestyle with a fast growth compared to plants and the ease of generating genetically engineered strains. This study focuses on photosynthetic production of the starting compounds of the phenylpropanoid pathway, trans-cinnamic acid and p-coumaric acid, in the unicellular cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis).

Results

A selected set of phenylalanine ammonia lyase (PAL) enzymes from different organisms was overexpressed in Synechocystis, and the productivities of the resulting strains compared. To further improve the titer of target compounds, we evaluated the use of stronger expression cassettes for increasing PAL protein levels, as well as knock-out of the laccase gene slr1573, as this was previously reported to prevent degradation of the target compounds in the cell. Finally, to investigate the effect of growth conditions on the production of trans-cinnamic and p-coumaric acids from Synechocystis, cultivation conditions promoting rapid, high density growth were tested. Comparing the different PALs, the highest specific titer was achieved for the strain AtC, expressing PAL from Arabidopsis thaliana. A subsequent increase of protein level did not improve the productivity. Production of target compounds in strains where the slr1573 laccase had been knocked out was found to be lower compared to strains with wild type background, and the Δslr1573 strains exhibited a strong phenotype of slower growth rate and lower pigment content. Application of a high-density cultivation system for the growth of production strains allowed reaching the highest total titers of trans-cinnamic and p-coumaric acids reported so far, at around 0.8 and 0.4 g L⁻¹, respectively, after 4 days.

Conclusions

Production of trans-cinnamic acid, unlike that of p-coumaric acid, is not limited by the protein level of heterologously expressed PAL in Synechocystis. High density cultivation led to higher titres of both products, while knocking out slr1573 did not have a positive effect on production. This work contributes to capability of exploiting the primary metabolism of cyanobacteria for sustainable production of plant phenylpropanoids.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01735-8.

Direct modulation of the gut microbiota as a therapeutic approach for Alzheimer's disease

Alzheimer's disease is a neurodegenerative disease characterized by a progressive decline in memory and cognitive functions. It is a multifactorial disease involving a wide range of pathological factors that are not fully understood. As supported by a growing amount of evidence in recent years, the gut microbiota plays an important role in the pathogenesis of Alzheimer's disease through the brain-gut-microbiota axis. This suggests that direct modulation of the gut microbiota can be a potential therapeutic target for Alzheimer's disease. This review summarizes recent research findings on the modulation of the gut microbiota by probiotic therapies and faecal microbiota transplantation for controlling the pathologies of Alzheimer's disease. Current limitations and future research directions of this field are also discussed.

Production of C20, C30 and C40 terpenes in the engineered phototrophic bacterium Rhodobacter capsulatus

Terpenes constitute one of the largest groups of secondary metabolites that are used, for example, as food-additives, fragrances or pharmaceuticals. Due to the formation of an intracytoplasmic membrane system and an efficient intrinsic tetraterpene pathway, the phototrophic α-proteobacterium Rhodobacter capsulatus offers favorable properties for the production of hydrophobic terpenes. However, research efforts have largely focused on sesquiterpene production. Recently, we have developed modular tools allowing to engineer the biosynthesis of terpene precursors. These tools were now applied to boost the biosynthesis of the diterpene casbene, the triterpene squalene and the tetraterpene β-carotene in R. capsulatus SB1003. Selected enzymes of the intrinsic isoprenoid pathway and the heterologous mevalonate (MVA) pathway were co-expressed together with the respective terpene synthases in various combinations. Remarkably, co-expression of genes ispA, idi and dxs enhanced the synthesis of casbene and β-carotene. In contrast, co-expression of precursor biosynthetic genes with the squalene synthase from Arabidopsis thaliana reduced squalene titers. Therefore, we further employed four alternative pro- and eukaryotic squalene synthases. Here, the synthase from Methylococcus capsulatus enabled highest product levels of 90 mg/L squalene upon co-expression with ispA. In summary, we demonstrate the applicability of R. capsulatus for the heterologous production of diverse terpene classes and provide relevant insights for further development of such platforms.

Pinosylvin inhibits migration and invasion of nasopharyngeal carcinoma cancer cells via regulation of epithelial‑mesenchymal transition and inhibition of MMP‑2

Nasopharyngeal carcinoma (NPC) is a tumor located in the nasopharynx with highly invasive and metastatic properties. Metastasis is a primary cause of mortality in patients with NPC. The terpenoid polyphenol pinosylvin is a known functional compound of the Pinus species that exhibits anti‑inflammatory effects; however, the effect of pinosylvin on human NPC cell migration and invasion is unclear. The present study aimed to investigate the functional role of pinosylvin in NPC cells (NPC‑039, NPC‑BM and RPMI 2650). Gap closure and Transwell assay indicated that pinosylvin at increasing concentrations inhibited migration and invasion of NPC‑039 and NPC‑BM cells. In addition to inhibiting the enzyme activity of MMP‑2, pinosylvin also decreased the protein expression levels of MMP‑2 and MMP‑9. Pinosylvin decreased the expression of vimentin and N‑cadherin and significantly increased the expression of zonula occludens‑1 and E‑cadherin in NPC cells. Additionally, pinosylvin suppressed the invasion and migration ability of NPC‑039 and NPC‑BM cells by mediating the p38, ERK1/2 and JNK1/2 pathways. The present results revealed that pinosylvin inhibited migration and invasion in NPC cells.

Bioproduction process of natural products and biopharmaceuticals: Biotechnological aspects

Decades of research have been put in place for developing sustainable routes of bioproduction of high commercial value natural products (NPs) on the global market. In the last few years alone, we have witnessed significant advances in the biotechnological production of NPs. The development of new methodologies has resulted in a better understanding of the metabolic flux within the organisms, which have driven manipulations to improve production of the target product. This was further realised due to the recent advances in the omics technologies such as genomics, transcriptomics, proteomics, metabolomics and secretomics, as well as systems and synthetic biology. Additionally, the combined application of novel engineering strategies has made possible avenues for enhancing the yield of these products in an efficient and economical way. Invention of high-throughput technologies such as next generation sequencing (NGS) and toolkits for genome editing Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated 9 (CRISPR/Cas9) have been the game changers and provided unprecedented opportunities to generate rationally designed synthetic circuits which can produce complex molecules. This review covers recent advances in the engineering of various hosts for the production of bioactive NPs and biopharmaceuticals. It also highlights general approaches and strategies to improve their biosynthesis with higher yields in a perspective of plants and microbes (bacteria, yeast and filamentous fungi). Although there are numerous reviews covering this topic on a selected species at a time, our approach herein is to give a comprehensive understanding about state-of-art technologies in different platforms of organisms.

Engineering and optimization of the 2-phenylethylglucosinolate production in Nicotiana benthamiana by combining biosynthetic genes from Barbarea vulgaris and Arabidopsis thaliana

2-Phenylethylglucosinolate (2PE) derived from homophenylalanine is present in plants of the Brassicales order as a defense compound. It is associated with multiple biological properties, including deterrent effects on pests and antimicrobial and health-promoting functions, due to its hydrolysis product 2-phenylethyl isothiocyanate, which confers 2PE as a potential application in agriculture and industry. In this study, we characterized the putative key genes for 2PE biosynthesis from Barbarea vulgaris W.T. Aiton and demonstrated the feasibility of engineering 2PE production in Nicotiana benthamiana Domin. We used different combinations of genes from B. vulgaris and Arabidopsis thaliana (L.) Heynh. to demonstrate that: (i) BvBCAT4 performed more efficiently than AtBCAT4 in biosynthesis of both homophenylalanine and dihomomethionine; (ii) MAM1 enzymes were critical for the chain-elongated profile, while CYP79F enzymes accepted both chain-elongated methionine and homophenylalanine; (iii) aliphatic but not aromatic core structure pathway catalyzed the 2PE biosynthesis; (iv) a chimeric pathway containing BvBCAT4, BvMAM1, AtIPMI and AtIPMDH1 resulted in a two-fold increase in 2PE production compared with the B. vulgaris-specific chain elongation pathway; and (v) profiles of chain-elongated products and glucosinolates partially mirrored the profiles in the gene donor plant, but were wider in N. benthamiana than in the native plants. Our study provides a strategy to produce the important homophenylalanine and 2PE in a heterologous host. Furthermore, chimeric engineering of the complex 2PE biosynthetic pathway enabled detailed understanding of catalytic properties of individual enzymes - a prerequisite for understanding biochemical evolution. The new-to-nature gene combinations have the potential for application in biotechnological and plant breeding.

Advanced Strategies for the Synthesis of Terpenoids in Yarrowia lipolytica

Terpenoids are an important class of secondary metabolites that play an important role in food, agriculture, and other fields. Microorganisms are rapidly emerging as a promising source for the production of terpenoids. As an oleaginous yeast, Yarrowia lipolytica contains a high lipid content which indicates that it must produce high amounts of acetyl-CoA, a necessary precursor for the biosynthesis of terpenoids. Y. lipolytica has a complete eukaryotic mevalonic acid (MVA) pathway but it has not yet seen commercial use due to its low productivity. Several metabolic engineering strategies have been developed to improve the terpenoids production of Y. lipolytica, including developing the orthogonal pathway for terpenoid synthesis, increasing the catalytic efficiency of terpenoids synthases, enhancing the supply of acetyl-CoA and NADPH, expressing rate-limiting genes, and modifying the branched pathway. Moreover, most of the acetyl-CoA is used to produce lipid, so it is an effective strategy to strike a balance of precursor distribution by rewiring the lipid biosynthesis pathway. Lastly, the latest developed non-homologous end-joining strategy for improving terpenoid production is introduced. This review summarizes the status and metabolic engineering strategies of terpenoids biosynthesis in Y. lipolytica and proposes new insights to move the field forward.

Synthesis of cembratriene-ol and cembratriene-diol in yeast via the MVA pathway

Background

Cembranoids are one kind of diterpenoids with multiple biological activities. The tobacco cembratriene-ol (CBT-ol) and cembratriene-diol (CBT-diol) have high anti-insect and anti-fungal activities, which is attracting great attentions for their potential usage in sustainable agriculture. Cembranoids were supposed to be formed through the 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway, yet the involvement of mevalonate (MVA) pathway in their synthesis remains unclear. Exploring the roles of MVA pathway in cembranoid synthesis could contribute not only to the technical approach but also to the molecular mechanism for cembranoid biosynthesis.

Results

We constructed vectors to express cembratriene-ol synthase (CBTS1) and its fusion protein (AD-CBTS1) containing an N-terminal GAL4 AD domain as a translation leader in yeast. Eventually, the modified enzyme AD-CBTS1 was successfully expressed, which further resulted in the production of CBT-ol in the yeast strain BY-T20 with enhanced MVA pathway for geranylgeranyl diphosphate (GGPP) production but not in other yeast strains with low GGPP supply. Subsequently, CBT-diol was also synthesized by co-expression of the modified enzyme AD-CBTS1 and BD-CYP450 in the yeast strain BY-T20.

Conclusions

We demonstrated that yeast is insensitive to the tobacco anti-fungal compound CBT-ol or CBT-diol and could be applied to their biosynthesis. This study further established a feasibility for cembranoid production via the MVA pathway and provided an alternative bio-approach for cembranoid biosynthesis in microbes.

Heterologous Production of β-Caryophyllene and Evaluation of Its Activity against Plant Pathogenic Fungi

Terpenoids constitute one of the largest and most diverse groups within the class of secondary metabolites, comprising over 80,000 compounds. They not only exhibit important functions in plant physiology but also have commercial potential in the biotechnological, pharmaceutical, and agricultural sectors due to their promising properties, including various bioactivities against pathogens, inflammations, and cancer. In this work, we therefore aimed to implement the plant sesquiterpenoid pathway leading to β-caryophyllene in the heterologous host Rhodobacter capsulatus and achieved a maximum production of 139 ± 31 mg L^-1 culture. As this sesquiterpene offers various beneficial anti-phytopathogenic activities, we evaluated the bioactivity of β-caryophyllene and its oxygenated derivative β-caryophyllene oxide against different phytopathogenic fungi. Here, both compounds significantly inhibited the growth of Sclerotinia sclerotiorum and Fusarium oxysporum by up to 40%, while growth of Alternaria brassicicola was only slightly affected, and Phoma lingam and Rhizoctonia solani were unaffected. At the same time, the compounds showed a promising low inhibitory profile for a variety of plant growth-promoting bacteria at suitable compound concentrations. Our observations thus give a first indication that β-caryophyllene and β-caryophyllene oxide are promising natural agents, which might be applicable for the management of certain plant pathogenic fungi in agricultural crop production.

Phytostilbenes as agrochemicals: biosynthesis, bioactivity, metabolic engineering and biotechnology

Covering: 1976 to 2020. Although constituting a limited chemical family, phytostilbenes represent an emblematic group of molecules among natural compounds. Ever since their discovery as antifungal compounds in plants and their ascribed role in human health and disease, phytostilbenes have never ceased to arouse interest for researchers, leading to a huge development of the literature in this field. Owing to this, the number of references to this class of compounds has reached the tens of thousands. The objective of this article is thus to offer an overview of the different aspects of these compounds through a large bibliography analysis of more than 500 articles. All the aspects regarding phytostilbenes will be covered including their chemistry and biochemistry, regulation of their biosynthesis, biological activities in plants, molecular engineering of stilbene pathways in plants and microbes as well as their biotechnological production by plant cell systems.

Enzymatic Synthesis of Glycans and Glycoconjugates

Glycoconjugates have great potential to improve human health in a multitude of different ways and fields. Prominent examples are human milk oligosaccharides and glycosaminoglycans. The typical choice for the production of homogeneous glycoconjugates is enzymatic synthesis. Through the availability of expression and purification protocols, recombinant Leloir glycosyltransferases are widely applied as catalysts for the synthesis of a wide range of glycoconjugates. Extensive utilization of these enzymes also depends on the availability of activated sugars as building blocks. Multi-enzyme cascades have proven a versatile technique to synthesize and in situ regenerate nucleotide sugar.In this chapter, the functions and mechanisms of Leloir glycosyltransferases are revisited, and the advantage of prokaryotic sources and production systems is discussed. Moreover, in vivo and in vitro pathways for the synthesis of nucleotide sugar are reviewed. In the second part, recent and prominent examples of the application of Leloir glycosyltransferase are given, i.e., the synthesis of glycosaminoglycans, glycoconjugate vaccines, and human milk oligosaccharides as well as the re-glycosylation of biopharmaceuticals, and the status of automated glycan assembly is revisited.

Saccharomyces Cerevisiae-An Interesting Producer of Bioactive Plant Polyphenolic Metabolites

Secondary phenolic metabolites are defined as valuable natural products synthesized by different organisms that are not essential for growth and development. These compounds play an essential role in plant defense mechanisms and an important role in the pharmaceutical, cosmetics, food, and agricultural industries. Despite the vast chemical diversity of natural compounds, their content in plants is very low, and, as a consequence, this eliminates the possibility of the production of these interesting secondary metabolites from plants. Therefore, microorganisms are widely used as cell factories by industrial biotechnology, in the production of different non-native compounds. Among microorganisms commonly used in biotechnological applications, yeast are a prominent host for the diverse secondary metabolite biosynthetic pathways. Saccharomyces cerevisiae is often regarded as a better host organism for the heterologous production of phenolic compounds, particularly if the expression of different plant genes is necessary.

Microbial Cell Factory for Efficiently Synthesizing Plant Natural Products via Optimizing the Location and Adaptation of Pathway on Genome Scale

Plant natural products (PNPs) possess important pharmacological activities and are widely used in cosmetics, health care products, and as food additives. Currently, most PNPs are mainly extracted from cultivated plants, and the yield is limited by the long growth cycle, climate change and complex processing steps, which makes the process unsustainable. However, the complex structure of PNPs significantly reduces the efficiency of chemical synthesis. With the development of metabolic engineering and synthetic biology, heterologous biosynthesis of PNPs in microbial cell factories offers an attractive alternative. Based on the in-depth mining and analysis of genome and transcriptome data, the biosynthetic pathways of a number of natural products have been successfully elucidated, which lays the crucial foundation for heterologous production. However, there are several problems in the microbial synthesis of PNPs, including toxicity of intermediates, low enzyme activity, multiple auxotrophic dependence, and uncontrollable metabolic network. Although various metabolic engineering strategies have been developed to solve these problems, optimizing the location and adaptation of pathways on the whole-genome scale is an important strategy in microorganisms. From this perspective, this review introduces the application of CRISPR/Cas9 in editing PNPs biosynthesis pathways in model microorganisms, the influences of pathway location, and the approaches for optimizing the adaptation between metabolic pathways and chassis hosts for facilitating PNPs biosynthesis.

Anthocyanins, multi-functional natural products of industrial relevance: Recent biotechnological advances

Anthocyanins, the color compounds of plants, are known for their wide applications in food, nutraceuticals and cosmetic industry. The biosynthetic pathway of anthocyanins is well established with the identification of potential key regulatory genes, which makes it possible to modulate its production by biotechnological means. Various biotechnological systems, including use of in vitro plant cell or tissue cultures as well as microorganisms have been used for the production of anthocyanins under controlled conditions, however, a wide range of factors affects their production. In addition, metabolic engineering technologies have also used the heterologous production of anthocyanins in recombinant plants and microorganisms. However, these approaches have mostly been tested at the lab- and pilot-scales, while very few up-scaling studies have been undertaken. Various challenges and ways of investigation are proposed here to improve anthocyanin production by using the in vitro plant cell or tissue culture and metabolic engineering of plants and microbial culture systems. All these methods are capable of modulating the production of anthocyanins , which can be further utilized for pharmaceutical, cosmetics and food applications.

Broadening the scope of biocatalytic C-C bond formation

The impeccable control over chemo-, site-, and stereoselectivity possible in enzymatic reactions has led to a surge in the development of new biocatalytic methods. Despite carbon-carbon (C-C) bonds providing the central framework for organic molecules, development of biocatalytic methods for their formation has been largely confined to the use of a select few lyases over the last several decades, limiting the types of C-C bond-forming transformations possible through biocatalytic methods. This Review provides an update on the suite of enzymes available for highly selective biocatalytic C-C bond formation. Examples will be discussed in reference to the (1) native activity of enzymes, (2) alteration of activity through protein or substrate engineering for broader applicability, and (3) utility of the biocatalyst for abiotic synthesis.

Engineering intracellular malonyl-CoA availability in microbial hosts and its impact on polyketide and fatty acid synthesis

Malonyl-CoA is an important central metabolite serving as the basic building block for the microbial synthesis of many pharmaceutically interesting polyketides, but also fatty acid-derived compounds including biofuels. Especially Saccharomyces cerevisiae, Escherichia coli, and Corynebacterium glutamicum have been engineered towards microbial synthesis of such compounds in recent years. However, developed strains and processes often suffer from insufficient productivity. Usually, tightly regulated intracellular malonyl-CoA availability is regarded as the decisive bottleneck limiting overall product formation. Therefore, metabolic engineering towards improved malonyl-CoA availability is essential to design efficient microbial cell factories for the production of polyketides and fatty acid derivatives. This review article summarizes metabolic engineering strategies to improve intracellular malonyl-CoA formation in industrially relevant microorganisms and its impact on productivity and product range, with a focus on polyketides and other malonyl-CoA-dependent products.Key Points• Malonyl-CoA is the central building block of polyketide synthesis.• Increasing acetyl-CoA supply is pivotal to improve malonyl-CoA availability.• Improved acetyl-CoA carboxylase activity increases availability of malonyl-CoA.• Fatty acid synthesis as an ambivalent target to improve malonyl-CoA supply.

Sustainable production of FAEE biodiesel using the oleaginous yeast Yarrowia lipolytica

Fatty acid ethyl esters (FAEEs) are fatty acid‐derived molecules and serve as an important form of biodiesel. The oleaginous yeast Yarrowia lipolytica is considered an ideal host platform for the production of fatty acid‐derived products due to its excellent lipid accumulation capacity. In this proof‐of‐principle study, several metabolic engineering strategies were applied for the overproduction of FAEE biodiesel in Y. lipolytica. Here, chromosome‐based co‐overexpression of two heterologous genes, namely, PDC1 (encoding pyruvate decarboxylase) and ADH1 (encoding alcohol dehydrogenase) from Saccharomyces cerevisiae, and the endogenous GAPDH (encoding glyceraldehyde‐3‐phosphate dehydrogenase) gene of Y. lipolytica resulted in successful biosynthesis of ethanol at 70.8 mg/L in Y. lipolytica. The engineered Y. lipolytica strain expressing the ethanol synthetic pathway together with a heterologous wax ester synthase (MhWS) exhibited the highest FAEE titer of 360.8 mg/L, which is 3.8‐fold higher than that of the control strain when 2% exogenous ethanol was added to the culture medium of Y. lipolytica. Furthermore, a synthetic microbial consortium comprising an engineered Y. lipolytica strain that heterologously expressed MhWS and a S. cerevisiae strain that could provide ethanol as a substrate for the production of the final product in the final engineered Y. lipolytica strain was created in this study. Finally, this synthetic consortium produced FAEE biodiesel at a titer of 4.8 mg/L under the optimum coculture conditions.

Identification of two new trichome-specific promoters of Nicotiana tabacum

MAIN CONCLUSION: pRbcS-T1 and pMALD1, two new trichome-specific promoters of Nicotiana tabacum, were identified and their strength and specificity were compared to those of previously described promoters in this species. Nicotiana tabacum has emerged as a suitable host for metabolic engineering of terpenoids and derivatives in tall glandular trichomes, which actively synthesize and secrete specialized metabolites. However, implementation of an entire biosynthetic pathway in glandular trichomes requires the identification of trichome-specific promoters to appropriately drive the expression of the transgenes needed to set up the desired pathway. In this context, RT-qPCR analysis was carried out on wild-type N. tabacum plants to compare the expression pattern and gene expression level of NtRbcS-T1 and NtMALD1, two newly identified genes expressed in glandular trichomes, with those of NtCYP71D16, NtCBTS2α, NtCPS2, and NtLTP1, which were reported in the literature to be specifically expressed in glandular trichomes. We show that NtRbcS-T1 and NtMALD1 are specifically expressed in glandular trichomes like NtCYP71D16, NtCBTS2α, and NtCPS2, while NtLTP1 is also expressed in other leaf tissues as well as in the stem. Transcriptional fusions of each of the six promoters to the GUS-VENUS reporter gene were introduced in N. tabacum by Agrobacterium-mediated transformation. Almost all transgenic lines displayed GUS activity in tall glandular trichomes, indicating that the appropriate cis regulatory elements were included in the selected promoter regions. However, unlike for the other promoters, no trichome-specific line was obtained for pNtLTP1:GUS-VENUS, in agreement with the RT-qPCR data. These data thus provide two new transcription promoters that could be used in metabolic engineering of glandular trichomes.

Immediate, multiplexed and sequential genome engineering facilitated by CRISPR/Cas9 in Saccharomyces cerevisiae

A method called Cas-3P allowing for immediate, multiplexed and sequential genome engineering was developed using one plasmid expressing Cas9 and three marked plasmid backbones (P1, P2 and P3) for guide RNA (gRNA) expression. The three marked gRNA plasmid backbones were recurred in a P1-P2-P3 order for sequential gene targeting, without construction of any additional plasmid and elimination of gRNA plasmid by induction in each round. The efficiency of direct gRNA plasmid curing mediated by Cas-3P was more than 40% in sequential gene targeting. Besides, Cas-3P allowed single-, double- and triple-loci gene targeting with an efficiency of 75%, 36.8% and 8.2% within 3-4 days, respectively. Through three sequential rounds of gene targeting within 10 days, S. cerevisiae was optimized for the production of patchoulol by replacing one promoter, overexpressing three genes and disrupting four genes. The work is important for practical application in the cell factory engineering of S. cerevisiae.

Off-Colony Screening of Biosynthetic Libraries by Rapid Laser-Enabled Mass Spectrometry

By leveraging advances in DNA synthesis and molecular cloning techniques, synthetic biology increasingly makes use of large construct libraries to explore large design spaces. For biosynthetic pathway engineering, the ability to screen these libraries for a variety of metabolites of interest is essential. If the metabolite of interest or the metabolic phenotype is not easily measurable, screening soon becomes a major bottleneck involving time-consuming culturing, sample preparation, and extraction. To address this, we demonstrate the use of automated laser-assisted rapid evaporative ionization mass spectrometry (LA-REIMS)-a form of ambient laser desorption ionization mass spectrometry-to perform rapid mass spectrometry analysis direct from agar plate yeast colonies without sample preparation or extraction. We use LA-REIMS to assess production levels of violacein and betulinic acid directly from yeast colonies at a rate of 6 colonies per minute. We then demonstrate the throughput enabled by LA-REIMS by screening over 450 yeast colonies within <4 h, while simultaneously generating recoverable glycerol stocks of each colony in real time. This showcases LA-REIMS as a prescreening tool to complement downstream quantification methods such as liquid chromatography-mass spectroscopy (LCMS). By prescreening several hundred colonies with LA-REIMS, we successfully isolate and verify a strain with a 2.5-fold improvement in betulinic acid production. Finally, we show that LA-REIMS can detect 20 out of a panel of 27 diverse biological molecules, demonstrating the broad applicability of LA-REIMS to metabolite detection. The rapid and automated nature of LA-REIMS makes this a valuable new technology to complement existing screening technologies currently employed in academic and industrial workflows.

Overexpression of a Novel Cytochrome P450 Promotes Flavonoid Biosynthesis and Osmotic Stress Tolerance in Transgenic Arabidopsis

Flavonoids are mainly associated with growth, development, and responses to diverse abiotic stresses in plants. A growing amount of data have demonstrated the biosynthesis of flavonoids through multienzyme complexes of which the membrane-bounded cytochrome P450 supergene family shares a crucial part. However, the explicit regulation mechanism of Cytochrome P450s related to flavonoid biosynthesis largely remains elusive. In the present study, we reported the identification of a stress-tolerant flavonoid biosynthetic CtCYP82G24 gene from Carthamus tinctorius. The transient transformation of CtCYP82G24 determined the subcellular localization to the cytosol. Heterologously expressed CtCYP82G24 was effective to catalyze the substrate-specific conversion, promoting the de novo biosynthesis of flavonoids in vitro. Furthermore, a qRT-PCR assay and the accumulation of metabolites demonstrated that the expression of CtCYP82G24 was effectively induced by Polyethylene glycol stress in transgenic Arabidopsis. In addition, the overexpression of CtCYP82G24 could also trigger expression levels of several other flavonoid biosynthetic genes in transgenic plants. Taken together, our findings suggest that CtCYP82G24 overexpression plays a decisive regulatory role in PEG-induced osmotic stress tolerance and alleviates flavonoid accumulation in transgenic Arabidopsis.

Engineered Rhodobacter capsulatus as a Phototrophic Platform Organism for the Synthesis of Plant Sesquiterpenoids

Sesquiterpenoids are a large class of natural compounds offering manifold properties valuable for food, cosmetics, agriculture, and pharma industry. Production in microorganisms is a sustainable approach to provide sesquiterpenoids for research and industrial use independent of their natural sources. This requires the functional transfer of the respective biocatalytic pathways in an adequate host microorganism offering a sufficient supply of precursors that is ideally adjusted to the individual demand of the recombinant biosynthesis route. The phototrophic purple bacterium Rhodobacter capsulatus offers unique physiological properties that are favorable for biosynthesis of hydrophobic terpenes. Under phototrophic conditions, it develops a large intracytoplasmic membrane suitable for hosting membrane-bound enzymes and metabolites of respective biosynthetic pathways. In addition, Rhodobacter harbors an intrinsic carotenoid biosynthesis that can be engineered toward the production of foreign terpenes. Here, we evaluate R. capsulatus as host for the production of plant sesquiterpenoids under phototrophic conditions using patchoulol and valencene as a proof of concept. The heterologous expression of patchoulol synthase PcPS from Pogostemon cablin as well as the valencene synthases CsVS from Citrus sinensis and CnVS from Callitropsis nootkatensis led to the production of the respective sesquiterpenoids in R. capsulatus. To analyze, if gradually adjustable formation of the key precursor farnesylpyrophosphate (FPP) is beneficial for sesquiterpene synthesis under phototrophic conditions, the intrinsic 1-deoxy-D-xylulose 5-phosphate (DXP) pathway genes as well as the heterologous mevalonate pathway genes were modularly expressed in various combinations. To this end, different plasmids and chromosomally integrated expression tools were developed harboring the strong and tightly controlled P_nif promoter for heterologous gene expression. Notably, comparative studies identified a distinct combination of precursor biosynthetic genes as best-performing setup for each of the tested sesquiterpene synthases. In summary, we could demonstrate that R. capsulatus is a promising alternative platform organism that is suited for sustainable sesquiterpenoid formation under phototrophic cultivation conditions. A modular engineering of R. capsulatus strains via tailored co-expression of FPP biosynthetic genes further allowed adaptation of sesquiterpene precursor formation to its catalytic conversion by different plant terpene synthases.

Engineered Production of Hapalindole Alkaloids in the Cyanobacterium Synechococcus sp. UTEX 2973

Cyanobacteria produce numerous valuable bioactive secondary metabolites (natural products) including alkaloids, isoprenoids, nonribosomal peptides, and polyketides. However, the genomic organization of the biosynthetic gene clusters, complex gene expression patterns, and low compound yields synthesized by the native producers currently limits access to the vast majority of these valuable molecules for detailed studies. Molecular cloning and expression of such clusters in heterotrophic hosts is often precarious owing to genetic and biochemical incompatibilities. Production of such biomolecules in photoautotrophic hosts analogous to the native producers is an attractive alternative that has been under-explored. Here, we describe engineering of the fast-growing cyanobacterium Synechococcus elongatus UTEX 2973 to produce key compounds of the hapalindole family of indole-isonitrile alkaloids. Engineering of the 42-kbp "fam" hapalindole pathway from the cyanobacterium Fischerella ambigua UTEX 1903 into S2973 was accomplished by rationally reconstructing six to seven core biosynthetic genes into synthetic operons. The resulting Synechococcus strains afforded controllable production of indole-isonitrile biosynthetic intermediates and hapalindoles H and 12-epi-hapalindole U at a titer of 0.75-3 mg/L. Exchanging genes encoding fam cyclase enzymes in the synthetic operons was employed to control the stereochemistry of the resulting product. Establishing a robust expression system provides a facile route to scalable levels of similar natural and new forms of bioactive hapalindole derivatives and its structural relatives (e.g., fischerindoles, welwitindolinones). Moreover, this versatile expression system represents a promising tool for exploring other functional characteristics of orphan gene products that mediate the remarkable biosynthesis of this important family of natural products.

Biotechnological Advances in Resveratrol Production and its Chemical Diversity

The very well-known bioactive natural product, resveratrol (3,5,4'-trihydroxystilbene), is a highly studied secondary metabolite produced by several plants, particularly grapes, passion fruit, white tea, and berries. It is in high demand not only because of its wide range of biological activities against various kinds of cardiovascular and nerve-related diseases, but also as important ingredients in pharmaceuticals and nutritional supplements. Due to its very low content in plants, multi-step isolation and purification processes, and environmental and chemical hazards issues, resveratrol extraction from plants is difficult, time consuming, impracticable, and unsustainable. Therefore, microbial hosts, such as Escherichia coli, Saccharomyces cerevisiae, and Corynebacterium glutamicum, are commonly used as an alternative production source by improvising resveratrol biosynthetic genes in them. The biosynthesis genes are rewired applying combinatorial biosynthetic systems, including metabolic engineering and synthetic biology, while optimizing the various production processes. The native biosynthesis of resveratrol is not present in microbes, which are easy to manipulate genetically, so the use of microbial hosts is increasing these days. This review will mainly focus on the recent biotechnological advances for the production of resveratrol, including the various strategies used to produce its chemically diverse derivatives.

Elucidation of the biosynthesis pathway and heterologous construction of a sustainable route for producing umbelliferone

Background

Coumarins play roles in many biological processes. Angelica decursiva is one of the major sources of coumarins in China. Due to increasing demand for coumarins in the marketplace, traditional extraction from plants is now considered economically insufficient and unsustainable. Microbial synthesis is a promising strategy for scalable production of coumarins. However, the biosynthetic pathway of coumarin remains poorly understood, and even more, the genes associated with this process have not been characterized in A. decursiva.

Results

RNA-seq was employed to elucidate the umbelliferone biosynthetic pathway. The results indicated that three enzymes, phenylalanine ammonia-lyase (PAL), 4-Coumarate: Coenzyme A Ligase (4CL), and p-coumaroyl CoA 2'-hydroxylase (C2'H) were involved in umbelliferone biosynthesis. Using the cloned genes, we generated a synthetic biology based microbial cell factory that produces coumarins from tyrosine utilizing Rhodotorula glutinis tyrosine ammonia lyase (RgTAL) to bypass cinnamic acid 4-hydroxylase (C4H). With metabolic engineering strategies, we deleted prephenate dehydratase (pheA), anthranilate synthase (trpE) and transcriptional regulatory protein (tyrR) and overexpressed six related genes involved in tyrosine biosynthesis, to drive the carbon flux from tyrosine. To overcome the limitation of 4CL, a virtual screening and site-specific mutagenesis-based protein engineering approach was applied. In addition, induction/culture conditions and different ions were employed to further improve the yield of umbelliferone. Finally, a yield of 356.59 mg/L umbelliferone was obtained.

Conclusions

The current study elucidated the umbelliferone biosynthesis pathway in A. decursiva. The results also demonstrated the feasibility of integrating gene mining with synthetic biology techniques to produce natural compounds.

Tailoring Corynebacterium glutamicum towards increased malonyl-CoA availability for efficient synthesis of the plant pentaketide noreugenin

Background

In the last years, different biotechnologically relevant microorganisms have been engineered for the synthesis of plant polyphenols such as flavonoids and stilbenes. However, low intracellular availability of malonyl-CoA as essential precursor for most plant polyphenols of interest is regarded as the decisive bottleneck preventing high product titers.

Results

In this study, Corynebacterium glutamicum, which emerged as promising cell factory for plant polyphenol production, was tailored by rational metabolic engineering towards providing significantly more malonyl-CoA for product synthesis. This was achieved by improving carbon source uptake, transcriptional deregulation of accBC and accD1 encoding the two subunits of the acetyl-CoA carboxylase (ACC), reduced flux into the tricarboxylic acid (TCA) cycle, and elimination of anaplerotic carboxylation of pyruvate. The constructed strains were used for the synthesis of the pharmacologically interesting plant pentaketide noreugenin, which is produced by plants such as Aloe arborescens from five molecules of malonyl-CoA. In this context, accumulation of the C₁/C₆ cyclized intermediate 1-(2,4,6-trihydroxyphenyl)butane-1,3-dione (TPBD) was observed, which could be fully cyclized to the bicyclic product noreugenin by acidification.

Conclusion

The best strain C. glutamicum Nor2 C5 mufasO_BCD1 P_O6-iolT1 ∆pyc allowed for synthesis of 53.32 mg/L (0.278 mM) noreugenin in CGXII medium supplemented with casamino acids within 24 h.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1117-x) contains supplementary material, which is available to authorized users.

Engineering Lactococcus lactis for the production of unusual anthocyanins using tea as substrate

Plant material rich in anthocyanins has been historically used in traditional medicines, but only recently have the specific pharmacological properties of these compounds been the target of extensive studies. In addition to their potential to modulate the development of various diseases, coloured anthocyanins are valuable natural alternatives commonly used to replace synthetic colourants in food industry. Exploitation of microbial hosts as cell factories is an attractive alternative to extraction of anthocyanins and other flavonoids from plant sources or chemical synthesis. In this study, we present the lactic acid bacterium Lactococcus lactis as an ideal host for the production of high-value plant-derived bioactive anthocyanins using green tea as substrate. Besides the anticipated red-purple compounds cyanidin and delphinidin, orange and yellow pyranoanthocyanidins with unexpected methylation patterns were produced from green tea by engineered L. lactis strains. The pyranoanthocyanins are currently attracting significant interest as one of the most important classes of anthocyanin derivatives and are mainly formed during the aging of wine, contributing to both colour and sensory experience.