Modular Engineering of Tyrosol Production in Escherichia coli

Metabolic engineering of Escherichia coli for 4-nitrophenylalanine production via the 4-aminophenylalanine synthetic pathway

The non-natural amino acid 4-nitrophenylalanine is a crucial pharmaceutical ingredient and has extensive utility in protein engineering. Here, we demonstrated the production of 4-nitrophenylalanine by Escherichia coli with AurF, 4-aminobenzoate N-oxygenase from Streptomyces thioluteus. Firstly, eight distinct gene combinations, encompassing four variants of papA and two of papBC, were evaluated to optimize the production of 4-aminophenylalanine, a precursor of 4-nitrophenylalanine. The strain co-expressing both pabAB from E. coli and papBC from Streptomyces venezuelae attained the highest 4-aminophenylalanine production. In a fed-batch fermenter cultivation, 4-aminophenylalanine production of 22.5 g/L was achieved. To produce 4-nitrophenylalanine from glucose, we constructed strains co-expressing AurF alongside the genes responsible for 4-aminophenylalanine synthesis. The subsequent optimization of the plasmid copy numbers carrying each gene set resulted in an increase in the 4-nitrophenylalanine production titer. Transcription analysis revealed that the expression level of the 4-aminophenylalanine biosynthetic genes markedly contributed to 4-nitrophenylalanine production. After optimizing batch fermentation conditions, the titer of 4-nitrophenylalanine increased to 2.22 g/L. Overall, these results provide the basis for industrial microbial production of 4-nitrophenylalanine, contributing to the advancement of biotechnological methodologies for generating non-natural amino acids with specific functionalities.

Two routes for tyrosol production by metabolic engineering of Corynebacterium glutamicum

BACKGROUND

The phenolic compound tyrosol is widely used in the pharmaceutical industry, owing to its beneficial effects on human health and its use as a precursor for key pharmaceuticals, including β1-receptor blockers. Tyrosol can be found in olive oil, but despite its natural biosynthesis in plants, low extraction efficiencies render microbial production a more viable alternative.

RESULTS

Here, we engineered the L-tyrosine overproducing Corynebacterium glutamicum strain AROM3 for the de novo production of tyrosol. Two routes were established and compared: one via 4-OH-phenylpyruvate as intermediate and the other via tyramine. We initially expected the first route to require heterologous expression of a prephenate dehydrogenase gene, given that C. glutamicum lacks this enzymatic function. However, heterologous expression of ARO10 from Saccharomyces cerevisiae (ARO10Sc), which encodes a phenylpyruvate decarboxylase, was sufficient to establish tyrosol production in strain AROM3. We identified that 4-OH-phenylpyruvate is synthesized from L-tyrosine by native aminotransferases, which is subsequently decarboxylated by Aro10Sc, and reduced to tyrosol by native alcohol dehydrogenases, leading to a titer of 9.4 ± 1.1 mM (1.30 ± 0.15 g/L). We identified the furfural dehydrogenase FudC as major enzyme involved in this pathway, as its gene deletion reduced tyrosol production by 75%. Given the instability of 4-OH-phenylpyruvate, the synthesis of tyrosol via the stable intermediate tyramine was pursued via the second route. Decarboxylation of L-tyrosine followed by oxidative deamination was accomplished by overexpression of the L-tyrosine decarboxylase gene tdc from Levilactobacillus brevis (tdcLb) and the tyramine oxidase gene tyo from Kocuria rhizophila (tyoKr). Using this route, tyrosol production was increased by 44% compared to the route via 4-OH-phenylpyruvate. With a division of labor approach by co-cultivating L-tyrosine producing strains that either express tdcLb or tyoKr, the highest titer of 14.1 ± 0.3 mM (1.95 ± 0.04 g/L) was achieved.

CONCLUSIONS

This study demonstrates the potential of endotoxin-free C. glutamicum as production host for the L-tyrosine-derived product tyrosol. Due to its L-arogenate pathway for L-tyrosine synthesis, the unstable 4-OH-phenylpyruvate could be excluded as intermediate in the Tdc-Tyo pathway, outcompeting the most often utilized production route via phenylpyruvate decarboxylases.

Real-time imaging of bacterial colony growth dynamics for cells with Type IV-A1 CRISPR-Cas activity

The Type IV-A1 CRISPR-Cas system of Pseudomonas oleovorans provides defense against mobile genetic elements in the absence of target DNA degradation. In recent studies, Escherichia coli BL21-AI cells with Type IV-A1 CRISPR-Cas activity displayed a heterogeneous colony growth phenotype. Here, we developed a convenient smartphone-mediated automatic remote-controlled time-lapse imaging system (SMARTIS), that enables monitoring of growing bacteria over time. The system's design includes a custom-built imaging box equipped with LED lights, an adjustable heating system and a smartphone that can be remotely controlled using freely available, user-friendly applications. SMARTIS allowed long-term observation of growing colonies and was utilized to analyze different growth behaviors of E. coli cells expressing Type IV-A1 CRISPR ribonucleoproteins. Our findings reveal that heterogeneity in colonies can emerge within hours of initial growth. We further examined the influence of different expression systems on bacterial growth and CRISPR interference activity and demonstrated that the observed heterogeneity of colony-forming units is strongly influenced by plasmid design and backbone identity. This study highlights the importance of careful assessment of heterogenous colony growth dynamics and describes a real-time imaging system with wide applications beyond the study of CRISPR-Cas activity in bacterial hosts.

Transcriptome analysis and reverse engineering verification of SNZ3Val125Ile and Pho3Asn134Asp revealed the mechanism of adaptive laboratory evolution to increase the yield of tyrosol in Saccharomyces cerevisiae strain S26-AE2

BACKGROUND

Tyrosol is an important drug precursor, and Saccharomyces cerevisiae is one of the main microorganisms that produces tyrosol. Although excessive metabolic modification increases the production of tyrosol, it also causes a decrease in the growth rate of yeast. Therefore, this study attempted to restore the growth of S. cerevisiae through adaptive evolution and further improve tyrosol production.

RESULTS

After the adaptive laboratory evolution of S. cerevisiae S26, three evolutionary strains were obtained. The biomass of strain S26-AE2 reached 17.82 g DCW/L in the presence of 100 g/L glucose, which was 15.33% higher than that of S26, and its tyrosol production reached 817.83 mg/L. The transcriptome analysis revealed that, upon exposure to 100 g/L glucose, the S26-AE2 strain may reduce the transcriptional regulation of glucose repression through decreased HXK2 expression. The expression of genes related to pyruvate synthesis was increased in strain S26-AE2. Meanwhile, the expression levels of most tricarboxylic acid cycle-related genes in S26-AE2 were increased when cultured with 20 g/L glucose. Furthermore, the amount of tyrosol produced by strain S26 with the SNZ3Val125Ile mutation increased by 17.01% compared with that of the control strain S26 following exposure to 100 g/L glucose.

CONCLUSIONS

In this study, a strain, S26-AE2, with good growth and tyrosol production performance was obtained by adaptive evolution. The transcriptome analysis revealed that the differences in the expression of genes involved in metabolic pathways in adaptive evolutionary strains may be related to yeast growth and tyrosol production. Further reverse engineering verified that the mutation of SNZ3 promoted tyrosol synthesis in S. cerevisiae in glucose-rich medium. This study provides a theoretical basis for the metabolic engineering of S. cerevisiae to synthesise tyrosol and its derivatives.

Production of aromatic amino acids and their derivatives by Escherichia coli and Corynebacterium glutamicum

Demand for aromatic amino acids (AAAs), such as L-phenylalanine, L-tyrosine, and L-tryptophan, has been increasing as they are used in animal feed and as precursors in the synthesis of industrial and pharmaceutical compounds. These AAAs are biosynthesized through the shikimate pathway in microorganisms and plants, and the reactions in the AAA biosynthesis pathways are strictly regulated at the levels of both gene expression and enzyme activity. Various attempts have been made to produce AAAs and their derivatives using microbial cells and to optimize production. In this review, we summarize the metabolic pathways involved in the biosynthesis of AAAs and their regulation and review recent research on AAA production using industrial bacteria, such as Escherichia coli and Corynebacterium glutamicum. Studies on fermentative production of AAA derivatives, including L-3,4-dihydroxyphenylalanine, tyrosol, and 3-hydroxytyrosol, are also discussed.

Engineering Escherichia coli for Efficient De Novo Synthesis of Salidroside

Salidroside is a high-value plant-derived glycoside with diverse biological activities, but the main industrial salidroside production method, extraction from Rhodiola plants, is insufficient to meet the growing market demand. The biosynthetic route via microbial fermentation is a sustainable and eco-friendly alternative method. De novo synthesis of the precursor tyrosol was established by introducing the ARO10 and ADH6 genes. Systematic metabolic engineering resulted in 3.0 g/L tyrosol, but accumulated tyrosol inhibited cell growth. Adaptive evolution produced an evolved strain with a 10.0% higher OD600 and a 3.3 g/L tyrosol titer. Introducing glucosyltransferase AtUGT85A1, and overexpressing phosphoglucose mutase pgm and UDP-glucose pyrophosphorylase galU, achieved de novo synthesis of salidroside. Furthermore, AtUGT85A1 was semirationally engineered, resulting in the A21G mutation, which enhanced salidroside production by 31.2%. The optimally engineered strain produced 16.8 g/L salidroside with 0.4 g/(L h) productivity in a 5 L bioreactor. This study laid a foundation for future industrial production of salidroside and provided important guidance for efficient biosynthesis of other tyrosol derivatives.

Semi-rational design and modification of phosphoketolase to improve the yield of tyrosol in Saccharomyces cerevisiae

Tyrosol is an important component of pharmaceuticals, nutraceuticals, and cosmetics, and their biosynthetic pathways are currently a hot research topic. d-Erythrose 4-phosphate is a key precursor for the biosynthesis of tyrosol in Saccharomyces cerevisiae. Hence, the flux of d-Erythrose 4-phosphate determined the yield of tyrosol synthesis. In this study, we first obtained an S. cerevisiae strain S19 with a tyrosol yield of 247.66 mg/L by metabolic engineering strategy. To increase the production of d-Erythrose 4-phosphate, highly active phosphoketolase BA-C was obtained by bioinformatics combined with tyrosol yield assay. The key residue sites 183, 217, and 320 were obtained by molecular docking, kinetic simulation, and tyrosol yield verification. After mutation, the highly efficient phosphoketolase BA-CHis320Met was obtained, with a 37.32 % increase in enzyme activity. The tyrosol production of strain S26 with BA-CHis320Arg increased by 43.05 % than strain S25 with BA-C and increased by 151.19 % compared with the strain S19 without phosphoketolase in a 20 L fermenter. The mining and modification of phosphoketolase will provide strong support for the de novo synthesis of aromatic compounds.

Efficient Biosynthesis of Salidroside via Artificial in Vivo enhanced UDP-Glucose System Using Cheap Sucrose as Substrate

Salidroside, a valuable phenylethanoid glycoside, is obtained from plants belonging to the Rhodiola genus, known for its diverse biological properties. At present, salidroside is still far from large-scale industrial production due to its lower titer and higher process cost. In this study, we have for the first time increased salidroside production by enhancing UDP-glucose supply in situ. We constructed an in vivo UDP-glucose regeneration system that works in conjunction with UDP-glucose transferase from Rhodiola innovatively to improve UDP-glucose availability. And a coculture was formed in order to enable de novo salidroside synthesis. Confronted with the influence of tyrosol on strain growth, an adaptive laboratory evolution strategy was implemented to enhance the strain's tolerance. Similarly, salidroside production was optimized through refinement of the fermentation medium, the inoculation ratio of the two microbes, and the inoculation size. The final salidroside titer reached 3.8 g/L. This was the highest titer achieved at the shake flask level in the existing reports. And this marked the first successful synthesis of salidroside in an in situ enhanced UDP-glucose system using sucrose. The cost was reduced by 93% due to the use of inexpensive substrates. This accomplishment laid a robust foundation for further investigations into the synthesis of other notable glycosides and natural compounds.

Optimization of tyrosol-producing pathway with tyrosine decarboxylase and tyramine oxidase in high-tyrosine-producing Escherichia coli

Tyrosol (4-hydroxyphenylethanol) is a phenolic compound used in the pharmaceutical and chemical industries. However, current supply methods, such as extraction from natural resources and chemical synthesis, have disadvantages from the viewpoint of cost and environmental protection. Here, we developed a tyrosol-producing Escherichia coli cell factory from a high-tyrosine-producing strain by expressing selected tyrosine decarboxylase-, tyramine oxidase (TYO)-, and medium-chain dehydrogenase/reductase (YahK)-encoding genes. The genes were controlled by the strong T7 promoter and integrated into the chromosome because of the advantages over plasmid-based systems. The strain produced a melanin-like pigment as a by-product, which is suggested to be formed from 4-hydroxyphenylacetaldehyde (a TYO product/YahK substrate). By using a culture medium containing a high concentration of glycerol, which was reported to enhance NADH supply required for YahK activity, the final titer of tyrosol reached 2.42 g/L in test tube-scale cultivation with a concomitant decrease in the amount of pigment. These results indicate that chromosomally integrated and T7 promoter-controlled gene expression system in E. coli is useful for high production of heterologous enzymes and might be applied for industrial production of useful compounds including tyrosine and tyrosol.

Promoting FADH2 Regeneration of Hydroxylation for High-Level Production of Hydroxytyrosol from Glycerol in Escherichia coli

Hydroxytyrosol is a natural polyphenolic compound widely used in the food and drug industries. The current commercial production of hydroxytyrosol relies mainly on plant extracts, which involve long extraction cycles and various raw materials. Microbial fermentation has potential value as an environmentally friendly and low-cost method. Here, a de novo biosynthetic pathway of hydroxytyrosol has been designed and constructed in an Escherichia coli strain with released tyrosine feedback inhibition. By introduction of hpaBC from E. coli and ARO10 and ADH6 from Saccharomyces cerevisiae, the de novo biosynthesis of hydroxytyrosol was achieved. An important finding in cofactor engineering is that the introduction of L-amino acid deaminase (LAAD) promotes not only cofactor regeneration but also metabolic flow redistribution. To further enhance the hydroxylation process, different 4-hydroxyphenylacetate 3-monooxygenase (hpaB) mutants and HpaBC proteins from different sources were screened. Finally, after optimization of the carbon source, pH, and seed medium, the optimum engineered strain produced 9.87 g/L hydroxytyrosol in a 5 L bioreactor. This represents the highest titer reported to date for de novo biosynthesis of hydroxytyrosol in microorganisms.

Efficient production of cembratriene-ol in Escherichia coli via systematic optimization

BACKGROUND

The tobacco leaf-derived cembratriene-ol exhibits anti-insect effects, but its content in plants is scarce. Cembratriene-ol is difficult and inefficiently chemically synthesised due to its complex structure. Moreover, the titer of reported recombinant hosts producing cembratriene-ol was low and cannot be applied to industrial production.

RESULTS

In this study, Pantoea ananatis geranylgeranyl diphosphate synthase (CrtE) and Nicotiana tabacum cembratriene-ol synthase (CBTS) were heterologously expressed to synthsize the cembratriene-ol in Escherichia coli. Overexpression of cbts*, the 1-deoxy-D-xylulose 5-phosphate synthase gene dxs, and isopentenyl diphosphate isomerase gene idi promoted the production of cembratriene-ol. The cembratriene-ol titer was 1.53-folds higher than that of E. coli Z17 due to the systematic regulation of ggpps, cbts*, dxs, and idi expression. The production of cembratriene-ol was boosted via the overexpression of genes ispA, ispD, and ispF. The production level of cembratriene-ol in the optimal medium at 72 h was 8.55-folds higher than that before fermentation optimisation. The cembratriene-ol titer in the 15-L fermenter reached 371.2 mg L^- 1, which was the highest titer reported.

CONCLUSION

In this study, the production of cembratriene-ol in E. coli was significantly enhanced via systematic optimization. It was suggested that the recombinant E. coli producing cembratriene-ol constructed in this study has potential for industrial production and applications.

Efficient whole cell biotransformation of tyrosol from L-tyrosine by engineered Escherichia coli

An engineered Escherichia coli was constructed by co-expressing L-amino acid deaminase, α-keto acid decarboxylase, alcohol dehydrogenase, and glucose dehydrogenase through two plasmids for tyrosol production. The activity of the rate-limiting enzyme L-amino acid deaminase from Cosenzaea myxofaciens (CmAAD) toward tyrosine was improved by structure-guided modification. The enzyme activity of triple mutant CmAAD V438G/K147V/R151E toward tyrosine was ~5.12-fold higher than that of the wild-type CmAAD. Secondly, the plasmid copy numbers and the gene orders were optimized to improve the titer of tyrosol. Finally, the recombinant strain CS-6 transformed 10 mM tyrosine into 9.56 ± 0.64 mM tyrosol at 45 ℃, and the space-time yield reached 0.478 mM·L^-1·h^-1. This study proposes a novel idea for the efficient and natural production of tyrosol, which has great potential for industrial application.

Engineering a Synthetic Pathway for Tyrosol Synthesis in Escherichia coli

Tyrosol is an aromatic compound with great value that is widely used in the food and pharmaceutical industry. In this study, we reported a synthetic pathway for converting p-coumaric acid (p-CA) into tyrosol in Escherichia coli. We found that the enzyme cascade comprising ferulic acid decarboxylase (FDC1) from Saccharomyces cerevisiae, styrene monooxygenase (SMO), styrene oxide isomerase (SOI) from Pseudomonas putida, and phenylacetaldehyde reductase (PAR) from Solanum lycopersicum could efficiently synthesize tyrosol from p-CA with a conversion rate over 90%. To further expand the range of substrates, we also introduced tyrosine ammonia-lyase (TAL) from Flavobacterium johnsoniae to connect the synthetic pathway with the endogenous l-tyrosine metabolism. We found that tyrosol could be efficiently produced from glycerol, reaching 545.51 mg/L tyrosol in a tyrosine-overproducing strain under shake flasks. In summary, we have established alternative routes for tyrosol synthesis from p-CA (a potential lignin-derived biomass), glucose, and glycerol.

Multi-modular engineering of Saccharomyces cerevisiae for high-titre production of tyrosol and salidroside

Tyrosol and its glycosylated product salidroside are important ingredients in pharmaceuticals, nutraceuticals and cosmetics. Despite the ability of Saccharomyces cerevisiae to naturally synthesize tyrosol, high yield from de novo synthesis remains a challenge. Here, we used metabolic engineering strategies to construct S. cerevisiae strains for high-level production of tyrosol and salidroside from glucose. First, tyrosol production was unlocked from feedback inhibition. Then, transketolase and ribose-5-phosphate ketol-isomerase were overexpressed to balance the supply of precursors. Next, chorismate synthase and chorismate mutase were overexpressed to maximize the aromatic amino acid flux towards tyrosol synthesis. Finally, the competing pathway was knocked out to further direct the carbon flux into tyrosol synthesis. Through a combination of these interventions, tyrosol titres reached 702.30 ± 0.41 mg l-1 in shake flasks, which were approximately 26-fold greater than that of the WT strain. RrU8GT33 from Rhodiola rosea was also applied to cells and maximized salidroside production from tyrosol in S. cerevisiae. Salidroside titres of 1575.45 ± 19.35 mg l-1 were accomplished in shake flasks. Furthermore, titres of 9.90 ± 0.06 g l-1 of tyrosol and 26.55 ± 0.43 g l-1 of salidroside were achieved in 5 l bioreactors, both are the highest titres reported to date. The synergistic engineering strategies presented in this study could be further applied to increase the production of high value-added aromatic compounds derived from the aromatic amino acid biosynthesis pathway in S. cerevisiae.

De novo biosynthesis of tyrosol acetate and hydroxytyrosol acetate from glucose in engineered Escherichia coli

Tyrosol and hydroxytyrosol derived from virgin olive oil and olives extract, have wide applications both as functional food components and as nutraceuticals. However, they have low bioavailability due to their low absorption and high metabolism in human liver and small intestine. Acetylation of tyrosol and hydroxytyrosol can effectively improve their bioavailability and thus increase their potential use in the food and cosmeceutical industries. There is no report on the bioproductin of tyrosol acetate and hydroxytyrosol acetate so far. Thus, it is of great significance to develop microbial cell factories for achieving tyrosol acetate or hydroxytyrosol acetate biosynthesis. In this study, a de novo biosynthetic pathway for the production of tyrosol acetate and hydroxytyrosol acetate was constructed in Escherichia coli. First, an engineered E. coli that allows production of tyrosol from simple carbon sources was established. Four aldehyde reductases were compared, and it was found that yeaE is the best aldehyde reductase for tyrosol accumulation. Subsequently, the pathway was extended for tyrosol acetate production by further overexpression of alcohol acetyltransferase ATF1 for the conversion of tyrosol to tyrosol acetate. Finally, the pathway was further extended for hydroxytyrosol acetate production by overexpression of 4-hydroxyphenylacetate 3-hydroxylase HpaBC.

Chromosome Engineering To Generate Plasmid-Free Phenylalanine- and Tyrosine-Overproducing Escherichia coli Strains That Can Be Applied in the Generation of Aromatic-Compound-Producing Bacteria

Many phenylalanine- and tyrosine-producing strains have used plasmid-based overexpression of pathway genes. The resulting strains achieved high titers and yields of phenylalanine and tyrosine. Chromosomally engineered, plasmid-free producers have shown lower titers and yields than plasmid-based strains, but the former are advantageous in terms of cultivation cost and public health/environmental risk. Therefore, we engineered here the Escherichia coli chromosome to create superior phenylalanine- and tyrosine-overproducing strains that did not depend on plasmid-based expression. Integration into the E. coli chromosome of two central metabolic pathway genes (ppsA and tktA) and eight shikimate pathway genes (aroA, aroB, aroC, aroD, aroE, aroG^fbr , aroL, and pheA^fbr ), controlled by the T7lac promoter, resulted in excellent titers and yields of phenylalanine; the superscript "fbr" indicates that the enzyme encoded by the gene was feedback resistant. The generated strain could be changed to be a superior tyrosine-producing strain by replacing pheA^fbr with tyrA^fbr A rational approach revealed that integration of seven genes (ppsA, tktA, aroA, aroB, aroC, aroG^fbr , and pheA^fbr ) was necessary as the minimum gene set for high-yield phenylalanine production in E. coli MG1655 (tyrR, adhE, ldhA, pykF, pflDC, and ascF deletant). The phenylalanine- and tyrosine-producing strains were further applied to generate phenyllactic acid-, 4-hydroxyphenyllactic acid-, tyramine-, and tyrosol-producing strains; yield of these aromatic compounds increased proportionally to the increase in phenylalanine and tyrosine yields.IMPORTANCE Plasmid-free strains for aromatic compound production are desired in the aspect of industrial application. However, the yields of phenylalanine and tyrosine have been considerably lower in plasmid-free strains than in plasmid-based strains. The significance of this research is that we succeeded in generating superior plasmid-free phenylalanine- and tyrosine-producing strains by engineering the E. coli chromosome, which was comparable to that in plasmid-based strains. The generated strains have a potential to generate superior strains for the production of aromatic compounds. Actually, we demonstrated that four kinds of aromatic compounds could be produced from glucose with high yields (e.g., 0.28 g tyrosol/g glucose).