Progress in terpene synthesis strategies through engineering of Saccharomyces cerevisiae

Biotransformation of Patchouli Alcohol by Cladosporium cladosporioides and the Anti-Influenza Virus Activities of Biotransformation Products

The biotransformation of patchouli alcohol by Cladosporium cladosporioides afforded 31 products, including 21 new ones (1-3, 5, 6, 8-14, and 17-25). Their structures were determined by extensive spectroscopic data analysis (1H and 13C NMR, HSQC, HMBC, 1H-1H COSY, ROESY, and HRESIMS), and the absolute configuration of compounds 1, 2, 8, 9, and 17 was determined by single-crystal X-ray diffraction using Cu Kα radiation. Structurally, compounds 21-24 were patchoulol-type norsesquiterpenoids without Me-12. Among them, a Δ3(4) double bond existed in compounds 21 and 22; a three-membered ring was formed between C-4, C-5, and C-6 in compound 23; an epoxy moiety appeared between C-3 and C-4 in compound 24. Furthermore, the biotransformation products 9, 10, 12, and 25 showed potent anti-influenza virus activity with EC50 values of 2.11, 7.94, 20.87, and 3.45 μM, respectively.

Biosynthesis Progress of High-Energy-Density Liquid Fuels Derived from Terpenes

High-energy-density liquid fuels (HED fuels) are essential for volume-limited aerospace vehicles and could serve as energetic additives for conventional fuels. Terpene-derived HED biofuel is an important research field for green fuel synthesis. The direct extraction of terpenes from natural plants is environmentally unfriendly and costly. Designing efficient synthetic pathways in microorganisms to achieve high yields of terpenes shows great potential for the application of terpene-derived fuels. This review provides an overview of the current research progress of terpene-derived HED fuels, surveying terpene fuel properties and the current status of biosynthesis. Additionally, we systematically summarize the engineering strategies for biosynthesizing terpenes, including mining and engineering terpene synthases, optimizing metabolic pathways and cell-level optimization, such as the subcellular localization of terpene synthesis and adaptive evolution. This article will be helpful in providing insight into better developing terpene-derived HED fuels.

Spatiotemporal Regulation and Transport Engineering for Sustainable Production of Geraniol in Candida glycerinogenes

Geraniol is an attractive natural monoterpene with significant industrial and commercial value in the fields of pharmaceuticals, condiments, cosmetics, and bioenergy. The biosynthesis of monoterpenes suffers from the availability of key intermediates and enzyme-to-substrate accessibility. Here, we addressed these challenges in Candida glycerinogenes by a plasma membrane-anchoring strategy and achieved sustainable biosynthesis of geraniol using bagasse hydrolysate as substrate. On this basis, a remarkable 2.4-fold improvement in geraniol titer was achieved by combining spatial and temporal modulation strategies. In addition, enhanced geraniol transport and modulation of membrane lipid-associated metabolism effectively promoted the exocytosis of toxic monoterpenes, significantly improved the resistance of the engineered strain to monoterpenes and improved the growth of the strains, resulting in geraniol yield up to 1207.4 mg L-1 at shake flask level. Finally, 1835.2 mg L-1 geraniol was obtained in a 5 L bioreactor using undetoxified bagasse hydrolysate. Overall, our study has provided valuable insights into the plasma membrane engineering of C. glycerinogenes for the sustainable and green production of valuable compounds.

A robust yeast chassis: comprehensive characterization of a fast-growing Saccharomyces cerevisiae

Robust chassis are critical to facilitate advances in synthetic biology. This study describes a comprehensive characterization of a new yeast isolate Saccharomyces cerevisiae XP that grows faster than commonly used research and industrial S. cerevisiae strains. The genomic, transcriptomic, and metabolomic analyses suggest that the fast growth rate is, in part, due to the efficient electron transport chain and key growth factor synthesis. A toolbox for genetic manipulation of the yeast was developed; we used it to construct l-lactic acid producers for high lactate production. The development of genetically malleable yeast strains that grow faster than currently used strains may significantly enhance the uses of S. cerevisiae in biotechnology.IMPORTANCEYeast is known as an outstanding starting strain for constructing microbial cell factories. However, its growth rate restricts its application. A yeast strain XP, which grows fast in high concentrations of sugar and acidic environments, is revealed to demonstrate the potential in industrial applications. A toolbox was also built for its genetic manipulation including gene insertion, deletion, and ploidy transformation. The knowledge of its metabolism, which could guide the designing of genetic experiments, was generated with multi-omics analyses. This novel strain along with its toolbox was then tested by constructing an l-lactic acid efficient producer, which is conducive to the development of degradable plastics. This study highlights the remarkable competence of nonconventional yeast for applications in biotechnology.

Multi-modular metabolic engineering and efflux engineering for enhanced lycopene production in recombinant Saccharomyces cerevisiae

Lycopene has been widely used in the food industry and medical field due to its antioxidant, anti-cancer, and anti-inflammatory properties. However, achieving efficient manufacture of lycopene using chassis cells on an industrial scale remains a major challenge. Herein, we attempted to integrate multiple metabolic engineering strategies to establish an efficient and balanced lycopene biosynthetic system in Saccharomyces cerevisiae. First, the lycopene synthesis pathway was modularized to sequentially enhance the metabolic flux of the mevalonate pathway, the acetyl-CoA supply module, and lycopene exogenous enzymatic module. The modular operation enabled the efficient conversion of acetyl-CoA to downstream pathway of lycopene synthesis, resulting in a 3.1-fold increase of lycopene yield. Second, we introduced acetate as an exogenous carbon source and utilized an acetate-repressible promoter to replace the natural ERG9 promoter. This approach not only enhanced the supply of acetyl-CoA but also concurrently diminished the flux toward the competitive ergosterol pathway. As a result, a further 42.3% increase in lycopene production was observed. Third, we optimized NADPH supply and mitigated cytotoxicity by overexpressing ABC transporters to promote lycopene efflux. The obtained strain YLY-PDR11 showed a 12.7-fold increase in extracellular lycopene level compared to the control strain. Finally, the total lycopene yield reached 343.7 mg/L, which was 4.3 times higher than that of the initial strain YLY-04. Our results demonstrate that combining multi-modular metabolic engineering with efflux engineering is an effective approach to improve the production of lycopene. This strategy can also be applied to the overproduction of other desirable isoprenoid compounds with similar synthesis and storage patterns in S. cerevisiae.

ONE-SENTENCE SUMMARY

In this research, lycopene production in yeast was markedly enhanced by integrating a multi-modular approach, acetate signaling-based down-regulation of competitive pathways, and an efflux optimization strategy.

Boosting production of cembratriene-ol in Saccharomyces cerevisiae via systematic optimization

Cembratriene-ol is a good biodegradable biopesticide ingredient with future potential applications in the field of sustainable agriculture. Cembratriene-ol is a monocyclic diterpenoid compound that is synthesized only in the trichome gland of Nicotiana plants. In this study, geranylgeranyl diphosphate synthase gene ggpps from Taxus canadensis and cbts*Δp were heterologously expressed in Saccharomyces cerevisiae W303-1A to successfully synthesize cembratriene-ol. The titer of cembratriene-ol was increased by 1.84-fold compared to the control by overexpressing the S. cerevisiae bifunctional (2E,6E)-farnesyl diphosphate synthase genes ERG20 and cbts*Δp under one promoter PGAP . The titer of cembratriene-ol in the engineered S. cerevisiae BY4741 was increased by 1.39-fold compared to the engineered S. cerevisiae W303-1A. The titer of cembratriene-ol in the engineered S. cerevisiae BY4741 was increased by 2.22-fold compared to the control by overexpressing ERG20 and cbts*Δp, respectively, using two promoters PGAP . Cembratriene-ol was found to be successfully synthesized via the integrated expression of cbts*Δp, ggpps and ERG20 on the genome of S. cerevisiae BY4741. The titer of cembratriene-ol in S. cerevisiae S25 was further increased by 1.80-fold compared to the control via dynamic control of the squalene synthase gene ERG9. Overexpression of the genes cbts*Δp and ggpps using pY26-GPD-TEF in S. cerevisiae S25 with their integration expression increased the titer of cembratriene-ol by 26.1-fold compared to S. cerevisiae S25. The titer of cembratriene-ol was significantly enhanced by mitochondrial compartmentalized expression of cbts*Δp and ggpps, which was 76.3-fold higher than that of the initial strain constructed. It was indicated that the systematic optimization has great potential in facilitating high-level production of cembratriene-ol production in S. cerevisiae.

Essential oils as green promising alternatives to chemical preservatives for agri-food products: New insight into molecular mechanism, toxicity assessment, and safety profile

Microbial food spoilage caused by food-borne bacteria, molds, and associated toxic chemicals significantly alters the nutritional quality of food products and makes them unpalatable to the consumer. In view of potential adverse effects (resistance development, residual toxicity, and negative effects on consumer health) of some of the currently used preservative agents and consumer preferences towards safe, minimally processed, and chemical-free products, food industries are looking for natural alternatives to the chemical preservatives. In this context, essential oils (EOs) showed broad-range antimicrobial effectiveness, low toxicity, and diverse mechanisms of action, and could be considered promising natural plant-based antimicrobials. The existing technical barriers related to the screening of plants, extraction methods, characterization, dose optimization, and unpredicted mechanism of toxicity in the food system, could be overcome using recent scientific and technological advancements, especially bioinformatics, nanotechnology, and mathematical approaches. The review focused on the potential antimicrobial efficacy of EOs against food-borne microbes and the role of recent scientific technology and social networking platform in addressing the major obstacles with EOs-based antimicrobial agents. In addition, a detailed mechanistic understanding of the antimicrobial efficacy of EOs, safety profile, and risk assessment using bioinformatics approaches are summarized to explore their potential application as food preservatives.

Engineering Saccharomyces cerevisiae for synthesis of β-myrcene and (E)-β-ocimene

Monoterpenes are among the important natural plant terpenes. Monoterpenes usually have the characteristics of volatility and strong aroma. β-Myrcene and its isomer (E)-β-ocimene are typical acyclic monoterpenes. They are high-value monoterpenes that have been widely applied in foods, cosmetics, and medicines. However, large-scale commercial production of β-myrcene and (E)-β-ocimene is restricted by their production method that mainly involves extraction from plant essential oils. Currently, an alternative synthetic route utilizing an engineered microbial platform was proposed for effective production. This study used a Saccharomyces cerevisiae strain previously constructed for squalene production as the starting strain. Farnesyl diphosphate synthase (Erg20) expression was weakened by promoter replacement and screened for optimal myrcene synthase (MS) and ocimene synthase (OS) activities. In the resulting S. cerevisiae engineered for β-myrcene and (E)-β-ocimene synthesis, titers of β-myrcene and (E)-β-ocimene were enhanced by a fusion expressing a mutant Erg20* with the obtained monoterpene synthase and optimizing the added solvent in a two-phase fermentation system. Finally, by scaling up in a 5-L fermenter, 8.12 mg/L of β-myrcene was obtained, which was first reported in yeast, and 34.56 mg/L of (E)-β-ocimene was obtained, which is the highest reported to date. This study provides a new synthesis route for β-myrcene and (E)-β-ocimene.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03818-2.

Snapshot of the Probiotic Potential of Kluveromyces marxianus DMKU-1042 Using a Comparative Probiogenomics Approach

Kluyveromyces marxianus is a rapidly growing thermotolerant yeast that secretes a variety of lytic enzymes, utilizes different sugars, and produces ethanol. The probiotic potential of this yeast has not been well explored. To evaluate its probiotic potential, the yeast strain Kluyveromyces marxianus DMKU3-1042 was analyzed using next-generation sequencing technology. Analysis of the genomes showed that the yeast isolates had a GC content of 40.10-40.59%. The isolates had many genes related to glycerol and mannose metabolism, as well as genes for acetoin and butanediol metabolism, acetolactate synthase subunits, and lactic acid fermentation. The strain isolates were also found to possess genes for the synthesis of different vitamins and Coenzyme A. Genes related to heat and hyperosmotic shock tolerance, as well as protection against reactive oxygen species were also found. Additionally, the isolates contained genes for the synthesis of lysine, threonine, methionine, and cysteine, as well as genes with anticoagulation and anti-inflammatory properties. Based on our analysis, we concluded that the strain DMKU3-1042 possesses probiotic properties that make it suitable for use in food and feed supplementation.

Characterization of an efficient CRISPR-iCas9 system in Yarrowia lipolytica for the biosynthesis of carotenoids

The application of clustered regularly interspaced short palindromic repeats-Cas (CRISPR-Cas9) technology in the genetic modification of Yarrowia lipolytica is challenged by low efficiency and low throughput. Here, a highly efficient CRISPR-iCas9 (with D147Y and P411T mutants) genetic manipulation tool was established for Y. lipolytica, which was further utilized to integrate carotene synthetic key genes and significantly improve the target product yield. First, CRISPR-iCas9 could shorten the time of genetic modification and enable the rapid knockout of nonsense suppressors. iCas9 can lead to more than 98% knockout efficiency for NHEJ-mediated repair after optimal target disruption of a single gene, 100% knockout efficiency for a single gene-guided version, and more than 80% knockout efficiency for multiple genes simultaneously in Y. lipolytica. Subsequently, this technology allowed for rapid one-step integration of large fragments (up to 9902-bp) of genes into chromosomes. Finally, YL-ABTG and YL-ABTG2Z were further constructed through CRISPR-iCas9 integration of key genes in a one-step process, resulting in a maximum β-carotene and zeaxanthin content of 3.12 mg/g and 2.33 mg/g dry cell weight, respectively. Therefore, CRISPR-iCas9 technology provides a feasible approach to genetic modification for efficient biosynthesis of biological compounds in Y. lipolytica. KEY POINTS: • iCas9 with D147Y and P411T mutants improved the CRISPR efficiency in Y. lipolytica. • CRISPR-iCas9 achieved efficient gene knockout and integration in Y. lipolytica. • CRISPR-iCas9 rapidly modified Y. lipolytica for carotenoid bioproduction.

Quantifying Isoprenoids in the Ergosterol Biosynthesis by Gas Chromatography-Mass Spectrometry

The ergosterol pathway is a promising target for the development of new antifungals since its enzymes are essential for fungal cell growth. Appropriate screening assays are therefore needed that allow the identification of potential inhibitors. We developed a whole-cell screening method, which can be used to identify compounds interacting with the enzymes of isoprenoid biosynthesis, an important part of the ergosterol biosynthesis pathway. The method was validated according to the EMEA guideline on bioanalytical method validation. Aspergillus fumigatus hyphae and Saccharomyces cerevisiae cells were lysed mechanically in an aqueous buffer optimized for the enzymatic deconjugation of isoprenoid pyrophosphates. The residual alcohols were extracted, silylated and analyzed by GC-MS. The obtained isoprenoid pattern provides an indication of the inhibited enzyme, due to the accumulation of specific substrates. By analyzing terbinafine-treated A. fumigatus and mutant strains containing tunable gene copies of erg9 or erg1, respectively, the method was verified. Downregulation of erg9 resulted in a high accumulation of intracellular farnesol as well as elevated levels of geranylgeraniol and isoprenol. The decreased expression of erg1 as well as terbinafine treatment led to an increased squalene content. Additional analysis of growth medium revealed high farnesyl pyrophosphate levels extruded during erg9 downregulation.

Enhancement of β-Caryophyllene Biosynthesis in Saccharomyces cerevisiae via Synergistic Evolution of β-Caryophyllene Synthase and Engineering the Chassis

β-Caryophyllene is a plant-derived bicyclic sesquiterpene with multiple biological functions. β-Caryophyllene production by engineered Saccharomyces cerevisiae represents a promising technological route. However, the low catalytic activity of β-caryophyllene synthase (CPS) is one of the main restrictive factors for β-caryophyllene production. Here, directed evolution of the Artemisia annua CPS was performed, and variants of CPS enhancing the β-caryophyllene biosynthesis in S. cerevisiae were obtained, in which an E353D mutant enzyme presented large improvements in Vmax and Kcat. The Kcat/Km of the E353D mutant was 35.5% higher than that of wild-type CPS. Moreover, the E353D variant exhibited higher catalytic activity in much wider pH and temperature ranges. Thus, both the higher catalytic activity and the robustness of the E353D variant contribute to the 73.3% increase in β-caryophyllene production. Furthermore, the S. cerevisiae chassis was engineered by overexpressing genes related to β-alanine metabolism and MVA pathway to enhance the synthesis of the precursor, and ATP-binding cassette transporter gene variant STE6T1025N to improve the transmembrane transport of β-caryophyllene. The combined engineering of CPS and chassis resulted in 70.45 mg/L of β-caryophyllene after 48 h of cultivation in a test tube, which was 2.93-fold of that of the original strain. Finally, a β-caryophyllene yield of 594.05 mg/L was obtained by fed-batch fermentation, indicating the potential of β-caryophyllene production by yeast.

Focus and Insights into the Synthetic Biology-Mediated Chassis of Economically Important Fungi for the Production of High-Value Metabolites

Substantial progress has been achieved and knowledge gaps addressed in synthetic biology-mediated engineering of biological organisms to produce high-value metabolites. Bio-based products from fungi are extensively explored in the present era, attributed to their emerging importance in the industrial sector, healthcare, and food applications. The edible group of fungi and multiple fungal strains defines attractive biological resources for high-value metabolites comprising food additives, pigments, dyes, industrial chemicals, and antibiotics, including other compounds. In this direction, synthetic biology-mediated genetic chassis of fungal strains to enhance/add value to novel chemical entities of biological origin is opening new avenues in fungal biotechnology. While substantial success has been achieved in the genetic manipulation of economically viable fungi (including Saccharomyces cerevisiae) in the production of metabolites of socio-economic relevance, knowledge gaps/obstacles in fungal biology and engineering need to be remedied for complete exploitation of valuable fungal strains. Herein, the thematic article discusses the novel attributes of bio-based products from fungi and the creation of high-value engineered fungal strains to promote yield, bio-functionality, and value-addition of the metabolites of socio-economic value. Efforts have been made to discuss the existing limitations in fungal chassis and how the advances in synthetic biology provide a plausible solution.

Biosynthesis of monoterpenoid and sesquiterpenoid as natural flavors and fragrances

Terpenoids are a large class of plant-derived compounds, that constitute the main components of essential oils and are widely used as natural flavors and fragrances. The biosynthesis approach presents a promising alternative route in terpenoid production compared to plant extraction or chemical synthesis. In the past decade, the production of terpenoids using biotechnology has attracted broad attention from both academia and the industry. With the growing market of flavor and fragrance, the production of terpenoids directed by synthetic biology shows great potential in promoting future market prospects. Here, we reviewed the latest advances in terpenoid biosynthesis. The engineering strategies for biosynthetic terpenoids were systematically summarized from the enzyme, metabolic, and cellular dimensions. Additionally, we analyzed the key challenges from laboratory production to scalable production, such as key enzyme improvement, terpenoid toxicity, and volatility loss. To provide comprehensive technical guidance, we collected milestone examples of biosynthetic mono- and sesquiterpenoids, compared the current application status of chemical synthesis and biosynthesis in terpenoid production, and discussed the cost drivers based on the data of techno-economic assessment. It is expected to provide critical insights into developing translational research of terpenoid biomanufacturing.

High-Level Production of Patchoulol in Yarrowia lipolytica via Systematic Engineering Strategies

Patchoulol is an important sesquiterpene alcohol with a strong and lasting odor, which has led to prominent applications in perfumes and cosmetics. In this study, systematic metabolic engineering strategies were adopted to create an efficient yeast cell factory for patchoulol overproduction. First, a baseline strain was constructed by selecting a highly active patchoulol synthase. Subsequently, the mevalonate precursor pool was expanded to boost patchoulol synthesis. Moreover, a method for downregulating squalene synthesis based on Cu²⁺-repressible promoter was optimized, which significantly improved the patchoulol titer by 100.9% to 124 mg/L. In addition, a protein fusion strategy resulted in a final titer of 235 mg/L in shake flasks. Finally, 2.864 g/L patchoulol could be produced in a 5 L bioreactor, representing a remarkable 1684-fold increase compared to the baseline strain. To our knowledge, this is the highest patchoulol titer reported so far.

Global metabolic rewiring of the nonconventional yeast Ogataea polymorpha for biosynthesis of the sesquiterpenoid β-elemene

Bioproduction of natural products via microbial cell factories is a promising alternative to traditional plant extraction. Recently, nonconventional microorganisms have emerged as attractive chassis hosts for biomanufacturing. One such microorganism, Ogataea polymorpha is an industrial yeast used for protein expression with numerous advantages, such as thermal-tolerance, a wide substrate spectrum and high-density fermentation. Here, we systematically rewired the cellular metabolism of O. polymorpha to achieve high-level production of the sesquiterpenoid β-elemene by optimizing the mevalonate pathway, enhancing the supply of NADPH and acetyl-CoA, and downregulating competitive pathways. The engineered strain produced 509 mg/L and 4.7 g/L of β-elemene under batch and fed-batch fermentation, respectively. Therefore, this study identified the potential industrial application of O. polymorpha as a good microbial platform for producing sesquiterpenoids.

Overproduction of Patchoulol in Metabolically Engineered Komagataella phaffii

Patchoulol, a plant-derived sesquiterpene compound, is widely used in perfumes, cosmetics, and pharmaceuticals. Microbial production provides a promising alternative approach for the efficient and sustainable production of patchoulol. However, there are no systematic engineering studies on Komagataella phaffii aimed at achieving high-yield patchoulol production. Herein, by fusion overexpression of FPP synthase and patchoulol synthase (ERG20LPTS), increasing the precursor supply, adjusting the copy number of ERG20LPTS and PTS, and combined with adding auxiliary carbon source and methanol concentration optimization, we constructed a high-yield patchoulol-producing strain P6H53, which produced 149.64 mg/L patchoulol in shake-flask fermentation with methanol as the substrate. In fed-batch fermentation, strain P6H53 achieved the highest production (2.47 g/L, 21.48 mg/g DCW, and 283.25 mg/L/d) to date in a 5 L fermenter. This study will lay a good foundation for the development of K. phaffii as a promising chassis microbial cell for the synthesis of patchoulol and other sesquiterpenes with methanol as the carbon source.

Engineered Saccharomyces cerevisiae for the De Novo Biosynthesis of (-)-Menthol

Menthol, a high-value commodity monoterpenoid chemical, holds an important market share commercially because of its distinct functions. The menthol on the market mainly originates from plant extraction, which is facing challenges such as the seasonal fluctuations and long growth cycle of plants. Therefore, this study attempted to realize the de novo synthesis of menthol through microbial fermentation. First, through heterologous expression and subcellular localization observation, a synthetic route from glucose to (-)-menthol was successfully designed and constructed in Saccharomyces cerevisiae. Then, the mevalonate (MVA) pathway was enhanced, and the expression of farnesyl diphosphate synthase (ERG20) was dynamically regulated to improve the synthesis of D-limonene, a key precursor of (-)-menthol. Shake flask fermentation results showed that the D-limonene titer of the recombinant strain reached 459.59 mg/L. Next, the synthesis pathway from D-limonene to (-)-menthol was strengthened, and the fermentation medium was optimized. The (-)-menthol titer of 6.28 mg/L was obtained, implying that the de novo synthesis of menthol was successfully realized for the first time. This study provides a good foundation for the synthesis of menthol through microbial fermentation.

Application of Multiple Strategies To Debottleneck the Biosynthesis of Longifolene by Engineered Saccharomyces cerevisiae

Longifolene as an important sesquiterpene had enormous biological benefits. However, the low productivity of longifolene relying on chemical catalysis and plant extraction limited its wide application. Herein, the longifolene biosynthetic pathway was introduced into Saccharomyces cerevisiae, and multiple genetic strategies were applied to debottleneck the synthesis of longifolene, including the regulation of the rate-limiting enzymes, the elimination of the competitive pathways, the screening of the molecular chaperone to improve synthase activity, and the enhancement of the precursor supply. After combinationally applying these optimum strategies, the production of longifolene reached 27.30 mg/L in shake flasks and 1249 mg/L in fed-batch fermentation, respectively, which was the highest yield of longifolene reported thus far. It was demonstrated that the strategies applied in our work were effective in promoting the biosynthesis of longifolene, which not only laid a significant foundation for its industrial production but also provided a platform for the synthesis of other terpenoids.

Dual cytoplasmic-peroxisomal engineering for high-yield production of sesquiterpene α-humulene in Yarrowia lipolytica

The sesquiterpene α-humulene is an important plant natural product, which has been used in pharmaceutical industry due to the anti-inflammatory and anticancer activities. Although phytoextraction and chemical synthesis have previously been applied into α-humulene production, the low efficiency and high costs limit the development. In this study, Y. lipolytica was engineered as the robust cell factory for sustainable α-humulene production. First, a chassis with high α-humulene output in the cytoplasm was constructed by integrating α-humulene synthases with high catalytic activity, optimizing the flux of MVA and acetyl-CoA pathways. Subsequently, the strategy of dual cytoplasmic-peroxisomal engineering was adopted in Y. lipolytica, the best strain GQ3006 generated by introducing 31 copies of 12 different genes could produce 2280.3 ± 38.2 mg/L (98.7 ± 4.2 mg/g DCW) α-humulene, a 100-fold improvement relative to the baseline strain. In order to further improve the titer, a novel strategy for downregulation of squalene biosynthesis based on Cu²⁺ -repressible promoters was firstly established, which significantly improved the α-humulene titer by 54.2 % to 3516.6 ± 34.3 mg/L. Finally, the engineered strain could produce 21.7 g/L α-humulene in 5-L bioreactor, 6.8-fold higher than the highest α-humulene titer reported prior to this study. Overall, system metabolic engineering strategies used in this study provide a valuable reference for highly sustainable production of terpenoids in Y. lipolytica. This article is protected by copyright. All rights reserved.

Metabolic Engineering of Saccharomyces cerevisiae for Heterologous Carnosic Acid Production

Carnosic acid (CA), a phenolic tricyclic diterpene, has many biological effects, including anti-inflammatory, anticancer, antiobesity, and antidiabetic activities. In this study, an efficient biosynthetic pathway was constructed to produce CA in Saccharomyces cerevisiae. First, the CA precursor miltiradiene was synthesized, after which the CA production strain was constructed by integrating the genes encoding cytochrome P450 enzymes (P450s) and cytochrome P450 reductase (CPR) SmCPR. The CA titer was further increased by the coexpression of CYP76AH1 and SmCPR ∼t28SpCytb5 fusion proteins and the overexpression of different catalases to detoxify the hydrogen peroxide (H₂O₂). Finally, engineering of the endoplasmic reticulum and cofactor supply increased the CA titer to 24.65 mg/L in shake flasks and 75.18 mg/L in 5 L fed-batch fermentation. This study demonstrates that the ability of engineered yeast cells to synthesize CA can be improved through metabolic engineering and synthetic biology strategies, providing a theoretical basis for microbial synthesis of other diterpenoids.

The Analysis of Correlations Between Terpene Transformations and Fermentation Type of Apple Musts

We measured the concentration of 13 terpenes in musts of 3 different apple cultivars fermented spontaneously, with Ethanol RED yeast (Saccharomyces cerevisiae) or Cider Yeast (Saccharomyces bayanus). Then we analysed obtained data with PCA with various packages in R to assess how different types of fermentation and apple cultivars affected terpene profile. The most informative results of PCA were obtained in ‘psych’ package and they indicated that there were groups of terpenes which concentrations increased simultaneously, while for some other groups the content of particular compounds was negatively correlated. This suggests that the first group of terpenes originated from different substrates while the latter group could be obtained from the same compound. Our findings indicated new possible pathways of terpene transformation, e.g. linalool, citral and geraniol could transform into one another. Moreover, the role of S. bayanus in those processes remains unclear and it requires further consideration.

Identification of the sesquiterpene synthase AcTPS1 and high production of (-)-germacrene D in metabolically engineered Saccharomyces cerevisiae

Background

The sesquiterpene germacrene D is a highly promising product due to its wide variety of insecticidal activities and ability to serve as a precursor for many other sesquiterpenes. Biosynthesis of high value compounds through genome mining for synthases and metabolic engineering of microbial factories, especially Saccharomyces cerevisiae, has been proven to be an effective strategy. However, there have been no studies on the de novo synthesis of germacrene D from carbon sources in microbes. Hence, the construction of the S. cerevisiae cell factory to achieve high production of germacrene D is highly desirable.

Results

We identified five putative sesquiterpene synthases (AcTPS1 to AcTPS5) from Acremonium chrysogenum and the major product of AcTPS1 characterized by in vivo, in vitro reaction and NMR detection was revealed to be (–)-germacrene D. After systematically comparing twenty-one germacrene D synthases, AcTPS1 was found to generate the highest amount of (–)-germacrene D and was integrated into the terpene precursor-enhancing yeast strain, achieving 376.2 mg/L of (–)-germacrene D. Iterative engineering was performed to improve the production of (–)-germacrene D, including increasing the copy numbers of AcTPS1, tHMG1 and ERG20, and downregulating or knocking out other inhibitory factors (such as erg9, rox1, dpp1). Finally, the optimal strain LSc81 achieved 1.94 g/L (–)-germacrene D in shake-flask fermentation and 7.9 g/L (–)-germacrene D in a 5-L bioreactor, which is the highest reported (–)-germacrene D titer achieved to date.

Conclusion

We successfully achieved high production of (–)-germacrene D in S. cerevisiae through terpene synthase mining and metabolic engineering, providing an impressive example of microbial overproduction of high-value compounds.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01814-4.

Enhancing fluxes through the mevalonate pathway in Saccharomyces cerevisiae by engineering the HMGR and β‐alanine metabolism

Mevalonate (MVA) pathway is the core for terpene and sterol biosynthesis, whose metabolic flux influences the synthesis efficiency of such compounds. Saccharomyces cerevisiae is an attractive chassis for the native active MVA pathway. Here, the truncated form of Enterococcus faecalis MvaE with only 3‐Hydroxy‐3‐methylglutaryl coenzyme A reductase (HMGR) activity was found to be the most effective enzyme for MVA pathway flux using squalene as the metabolic marker, resulting in 431‐fold and 9‐fold increases of squalene content in haploid and industrial yeast strains respectively. Furthermore, a positive correlation between MVA metabolic flux and β‐alanine metabolic activity was found based on a metabolomic analysis. An industrial strain SQ3‐4 with high MVA metabolic flux was constructed by combined engineering HMGR activity, NADPH regeneration, cytosolic acetyl‐CoA supply and β‐alanine metabolism. The strain was further evaluated as the chassis for terpenoids production. Strain SQ3‐4‐CPS generated from expressing β‐caryophyllene synthase in SQ3‐4 produced 11.86 ± 0.09 mg l⁻¹ β‐caryophyllene, while strain SQ3‐5 resulted from down‐regulation of ERG1 in SQ3‐4 produced 408.88 ± 0.09 mg l⁻¹ squalene in shake flask cultivations. Strain SQ3‐5 produced 4.94 g l⁻¹ squalene in fed‐batch fermentation in cane molasses medium, indicating the promising potential for cost‐effective production of squalene.

Recent advances in the microbial production of squalene

Squalene is a triterpene hydrocarbon, a biochemical precursor for all steroids in plants and animals. It is a principal component of human surface lipids, in particular of sebum. Squalene has several applications in the food, pharmaceutical, and medical sectors. It is essentially used as a dietary supplement, vaccine adjuvant, moisturizer, cardio-protective agent, anti-tumor agent and natural antioxidant. With the increased demand for squalene along with regulations on shark-derived squalene, there is a need to find alternatives for squalene production which are low-cost as well as sustainable. Microbial platforms are being considered as a potential option to meet such challenges. Considerable progress has been made using both wild-type and engineered microbial strains for improved productivity and yields of squalene. Native strains for squalene production are usually limited by low growth rates and lesser titers. Metabolic engineering, which is a rational strain engineering tool, has enabled the development of microbial strains such as Saccharomyces cerevisiae and Yarrowia lipolytica, to overproduce the squalene in high titers. This review focuses on key strain engineering strategies involving both in-silico and in-vitro techniques. Emphasis is made on gene manipulations for improved precursor pool, enzyme modifications, cofactor regeneration, up-regulation of limiting reactions, and downregulation of competing reactions during squalene production. Process strategies and challenges related to both upstream and downstream during mass cultivation are detailed.

In silico target-based strain engineering of Saccharomyces cerevisiae for terpene precursor improvement

Systems-based metabolic engineering enables cells to enhance product formation by predicting gene knockout and overexpression targets using modeling tools. FOCuS, a novel metaheuristic tool, was used to predict flux improvement targets in terpenoid pathway using the genome-scale model of Saccharomyces cerevisiae, iMM904. Some of the key knockout target predicted includes LYS1, GAP1, AAT1, AAT2, TH17, KGD-m, MET14, PDC1 and ACO1. It was also observed that the knockout reactions belonged either to fatty acid biosynthesis, amino acid synthesis pathways or nucleotide biosynthesis pathways. Similarly, overexpression targets such as PFK1, FBA1, ZWF1, TDH1, PYC1, ALD6, TPI1, PDX1 and ENO1 were established using three different existing gene amplification algorithms. Most of the overexpression targets belonged to glycolytic and pentose phosphate pathways. Each of these targets had plausible role for improving flux toward sterol pathway and were seemingly not artifacts. Moreover, an in vitro study as validation was carried with overexpression of ALD6 and TPI1. It was found that there was an increase in squalene synthesis by 2.23- and 4.24- folds, respectively, when compared with control. In general, the rationale for predicting these in silico targets was attributed to either increasing the acetyl-CoA precursor pool or regeneration of NADPH, which increase the sterol pathway flux.

Production of sesquiterpene patchoulol in mitochondrion-engineered Saccharomyces cerevisiae

Patchoulol is a natural sesquiterpene, which is widely used in perfumes and cosmetics. In the work, the mitochondria of S. cerevisiae were engineered for patchoulol production. The patchoulol titer of mitochondria-compartmentalized strain (1.79 mg/L) was 2.71-fold higher than that of control strain (0.66 mg/L) using genome-integrated patchoulol synthase, indicating that mitochondria compartmentation resulted in higher concentration of FPP (farnesyl pyrophosphate) precursor for patchoulol production. Moreover, when fused FPP synthase and patchoulol synthase was overexpressed in the strain with a mitochondria-localized DMAPP (dimethylallyl diphosphate) pathway, the production of patchoulol increased significantly to 19.24 mg/L, indicating more precursors were provided for patchoulol production. Nevertheless, the introduction of excess foreign proteins into mitochondria might cause a certain stress on mitochondria and showed a negative effect on the growth of yeast cells, which could hinder the expression of foreign pathways and reduce the patchoulol production. In conclusion, mitochondria-engineered yeast cells showed important potential for the enhanced biosynthesis of patchoulol, and further engineering could be considered based on the present work.

Metabolic Engineering of Saccharomyces cerevisiae for High-Level Friedelin via Genetic Manipulation

Friedelin, the most rearranged pentacyclic triterpene, also exhibits remarkable pharmacological and anti-insect activities. In particular, celastrol with friedelin as the skeleton, which is derived from the medicinal plant Tripterygium wilfordii, is a promising drug due to its anticancer and antiobesity activities. Although a previous study achieved friedelin production using engineered Saccharomyces cerevisiae, strains capable of producing high-level friedelin have not been stably engineered. In this study, a combined strategy was employed with integration of endogenous pathway genes into the genome and knockout of inhibiting genes by CRISPR/Cas9 technology, which successfully engineered multiple strains. After introducing an efficient TwOSC1^T502E, all strains with genetic integration (tHMG1, ERG1, ERG20, ERG9, POS5, or UPC2.1) showed a 3.0∼6.8-fold increase in friedelin production compared with strain BY4741. Through further double knockout of inhibiting genes, only strains GD1 and GD3 produced higher yields. Moreover, strains GQ1 and GQ3 with quadruple mutants (bts1; rox1; ypl062w; yjl064w) displayed similar increases. Finally, the dominant strain GQ1 with TwOSC1^T502E was cultured in an optimized medium in shake flasks, and the final yield of friedelin reached 63.91 ± 2.45 mg/L, which was approximately 65-fold higher than that of the wild-type strain BY4741 and 229% higher than that in ordinary SD-His-Ura medium. It was the highest titer for friedelin production to date. Our work provides a good example for triterpenoid production in microbial cell factories and lays a solid foundation for the mining, pathway analysis, and efficient production of valuable triterpenoids with friedelin as the skeleton.

Enhancing Squalene Production in Saccharomyces cerevisiae by Metabolic Engineering and Random Mutagenesis

Squalene is an important polyunsaturated triterpene with wide applications in the food, cosmetics, and pharmaceutical industries. Currently, the main method for squalene production is extraction from oil-producing plants, but the scale is limited. The microbial fermentation with Saccharomyces cerevisiae still needs improvement to be economically viable. This study aimed to improve squalene production by metabolic engineering and random mutagenesis. First, the mevalonate (MVA) pathway was enhanced, by integrating tHMG1 and IDI1 into multi-copy site Ty2. Subsequently, the ACL gene from Yarrowia lipolytica, encoding citrate lyase was introduced and the β-oxidation pathway was enhanced with multiple copies of key genes. In addition, a high throughput screening strategy based on Nile red staining was established for high squalene-producer screening. After treatment with ARTP mutagenesis, a higher-producing mutant was obtained, with squalene production enhanced by 18.4%. A two-stage fermentation of this mutant in a 5 L bioreactor produced 8.2 g/L of squalene. These findings may facilitate the development of industrial squalene production by fermentation and potentially, other terpenoids.

Saccharomyces cerevisiae as a Heterologous Host for Natural Products

Cell factories can provide a sustainable supply of natural products with applications as pharmaceuticals, food-additives or biofuels. Besides being an important model organism for eukaryotic systems, Saccharomyces cerevisiae is used as a chassis for the heterologous production of natural products. Its success as a cell factory can be attributed to the vast knowledge accumulated over decades of research, its overall ease of engineering and its robustness. Many methods and toolkits have been developed by the yeast metabolic engineering community with the aim of simplifying and accelerating the engineering process.In this chapter, a range of methodologies are highlighted, which can be used to develop novel natural product cell factories or to improve titer, rate and yields of an existing cell factory with the goal of developing an industrially relevant strain. The addressed topics are applicable for different stages of a cell factory engineering project and include the choice of a natural product platform strain, expression cassette design for heterologous or native genes, basic and advanced genetic engineering strategies, and library screening methods using biosensors. The many engineering methods available and the examples of yeast cell factories underline the importance and future potential of this host for industrial production of natural products.

Engineering Rhodosporidium toruloides for limonene production

BACKGROUND

Limonene is a widely used monoterpene in the production of food, pharmaceuticals, biofuels, etc. The objective of this work was to engineer Rhodosporidium toruloides as a cell factory for the production of limonene.

RESULTS

By overexpressing the limonene synthase (LS), neryl pyrophosphate synthase (NPPS)/geranyl pyrophosphate synthase and the native hydroxy-methyl-glutaryl-CoA reductase (HMGR), we established a baseline for limonene production based on the mevalonate route in Rhodosporidium toruloides. To further enhance the limonene titer, the acetoacetyl-CoA thiolase/HMGR (EfMvaE) and mevalonate synthase (EfMvaS) from Enterococcus faecalis, the mevalonate kinase from Methanosarcina mazei (MmMK) and the chimeric enzyme NPPS-LS were introduced in the carotenogenesis-deficient strain. The resulting strains produced a maximum limonene titer of 393.5 mg/L.

CONCLUSION

In this study, we successfully engineered the carotenogenesis yeast R. toruloides to produce limonene. This is the first report on engineering R. toruloides toward limonene production based on NPP and the fusion protein SltNPPS-CltLS. The results demonstrated that R. toruloides is viable for limonene production, which would provide insights into microbial production of valuable monoterpenes.

Functional Characterization and Structural Insights Into Stereoselectivity of Pulegone Reductase in Menthol Biosynthesis

Monoterpenoids are the main components of plant essential oils and the active components of some traditional Chinese medicinal herbs like Mentha haplocalyx Briq., Nepeta tenuifolia Briq., Perilla frutescens (L.) Britt and Pogostemin cablin (Blanco) Benth. Pulegone reductase is the key enzyme in the biosynthesis of menthol and is required for the stereoselective reduction of the Δ^2,8 double bond of pulegone to produce the major intermediate menthone, thus determining the stereochemistry of menthol. However, the structural basis and mechanism underlying the stereoselectivity of pulegone reductase remain poorly understood. In this study, we characterized a novel (-)-pulegone reductase from Nepeta tenuifolia (NtPR), which can catalyze (-)-pulegone to (+)-menthone and (-)-isomenthone through our RNA-seq, bioinformatic analysis in combination with in vitro enzyme activity assay, and determined the structure of (+)-pulegone reductase from M. piperita (MpPR) by using X-ray crystallography, molecular modeling and docking, site-directed mutagenesis, molecular dynamics simulations, and biochemical analysis. We identified and validated the critical residues in the crystal structure of MpPR involved in the binding of the substrate pulegone. We also further identified that residues Leu56, Val282, and Val284 determine the stereoselectivity of the substrate pulegone, and mainly contributes to the product stereoselectivity. This work not only provides a starting point for the understanding of stereoselectivity of pulegone reductases, but also offers a basis for the engineering of menthone/menthol biosynthetic enzymes to achieve high-titer, industrial-scale production of enantiomerically pure products.

Metabolic engineering strategies for de novo biosynthesis of sterols and steroids in yeast

Steroidal compounds are of great interest in the pharmaceutical field, with steroidal drugs as the second largest category of medicine in the world. Advances in synthetic biology and metabolic engineering have enabled de novo biosynthesis of sterols and steroids in yeast, which is a green and safe production route for these valuable steroidal compounds. In this review, we summarize the metabolic engineering strategies developed and employed for improving the de novo biosynthesis of sterols and steroids in yeast based on the regulation mechanisms, and introduce the recent progresses in de novo synthesis of some typical sterols and steroids in yeast. The remaining challenges and future perspectives are also discussed.

Advances in production and structural derivatization of the promising molecule ursolic acid

Ursolic acid (UA) is a ursane-type pentacyclic triterpenoid compound, naturally produced in plants via specialized metabolism and exhibits vast range of remarkable physiological activities and pharmacological manifestations. Owing to significant safety and efficacy in different medical conditions, UA may serve as a backbone to produce its derivatives with novel therapeutic functions. This review aims to provide ideas for exploring more diverse structures to improve UA pharmacological activity and increasing its biological yield to meet the industrial requirements by systematically reviewing the current research progress of UA. We first provides an overview of the pharmacological activities, acquisition methods and structural modifications of UA. Among them, we focused on the synthetic modifications of UA to yield valuable derivatives with enhanced therapeutic potential. Furthermore, harnessing the essential advances for green synthesis of UA and its derivatives by advent of metabolic engineering and synthetic biology are of great concern. In this regard, all pivotal advances for enhancing the production of UA have been discussed. In combination with the advantages of UA biosynthesis and transformation strategy, large-scale microbial production of UA is a promising platform for further exploration.

Engineering of cis-Element in Saccharomyces cerevisiae for Efficient Accumulation of Value-Added Compound Squalene via Downregulation of the Downstream Metabolic Flux

Transcriptional downregulation is widely used for metabolic flux control. Here, marO, a cis-element of Escherichia coli mar operator, was explored to engineer promoters of Saccharomyces cerevisiae for downregulation. First, the ADH1 promoter (P_ADH1) and its enhanced variant P_UADH1 were engineered by insertion of marO into different sites, which resulted in decrease in both gfp5 transcription and GFP fluorescence intensity to various degrees. Then, marO was applied to engineer the native ERG1 and ERG11 promoters due to their importance for accumulation of value-added intermediates squalene and lanosterol. Elevated squalene content (4.9-fold) or lanosterol content (4.8-fold) and 91 or 28% decrease in ergosterol content resulted from the marO-engineered promoter P_ERG1(M5) or P_ERG11(M3), respectively, indicating the validity of the marO-engineered promoters in metabolic flux control. Furthermore, squalene production of 3.53 g/L from cane molasses, a cheap and bulk substrate, suggested the cost-effective and promising potential for squalene production.

Advances on (+)-nootkatone microbial biosynthesis and its related enzymes

(+)-Nootkatone is an important functional sesquiterpene and is comprehensively used in pharmaceutical, cosmetic, agricultural and food flavor industries. However, (+)-nootkatone is accumulated trace amounts in plants, and the demand for industry is mainly met by chemical methods which is harmful to the environment. The oxygen-containing sesquiterpenes prepared using microbial methods can be considered as "natural." Microbial transformation has the advantages of mild reaction conditions, high efficiency, environmental protection, and strong stereoselectivity, and has become an important method for the production of natural spices. The microbial biosynthesis of (+)-nootkatone from the main precursor (+)-valencene is summarized in this paper. Whole-cell systems of fungi, bacteria, microalgae, and plant cells have been employed. It was described that the enzymes involved in the microbial biosynthesis of (+)-nootkatone, including cytochrome p450 enzymes, laccase, lipoxygenase, and so on. More recently, the related enzymes were expressed in microbial hosts to heterologous produce (+)-nootkatone, such as Escherichia coli, Pichia pastoris, Yarrowia lipolytica, and Saccharomyces cerevisiae. Finally, the development direction of research for realizing industrialization of microbial transformation was summarized and it provided many options for future improved bioprocesses.

Production of (-)-α-bisabolol in metabolically engineered Saccharomyces cerevisiae

(-)-α-Bisabolol is a natural monocyclic sesquiterpene alcohol present in German chamomile and has been used as an ingredient of functional foods, cosmetics and pharmaceuticals. In this study, metabolic engineering strategies were attempted to produce (-)-α-bisabolol in Saccharomyces cerevisiae. The codon-optimized MrBBS gene coding for (-)-α-bisabolol synthase from Matricaria recutita was expressed in S. cerevisiae for (-)-α-bisabolol production. The resulting strain (DM) produced 9.5 mg/L of (-)-α-bisabolol in 24 h of batch culture. Additionally, the mevalonate pathway was intensified by introducing a truncated HMG1 gene coding for HMG-CoA reductase and ERG10 encoding acetyl-CoA thiolase. The resulting strain (DtEM) produced a 2.9-fold increased concentration of (-)-α-bisabolol than the DM strain. To increase the acetyl-CoA pool, the ACS1 gene coding for acetyl-CoA synthetase was also overexpressed in the DtEM strain. Finally, the DtEMA strain produced 124 mg/L of (-)-α-bisabolol with 2.7 mg/L-h of productivity in a fed-batch fermentation, which were 13 and 6.8 times higher than the DM strain in batch culture, respectively. Conclusively, these metabolically-engineered approaches might pave the way for the sustainable production of other sesquiterpenes in engineered S. cerevisiae.

Genetic engineering of yeast, filamentous fungi and bacteria for terpene production and applications in food industry

Terpenes are a major class of natural aromatic compounds in grapes and wines to offer the characteristic flavor and aroma, serving as important quality traits of wine products. Saccharomyces cerevisiae represents an excellent cell factory platform for large-scale bio-based terpene production. This review describes the biosynthetic pathways of terpenes in different organisms. The metabolic engineering of S. cerevisiae for promoting terpene biosynthesis and the alternative microbial engineering platforms including filamentous fungi and Escherichia coli are also elaborated. Additionally, the potential applications of the terpene products from engineered microorganisms in food and beverage industries are also discussed. This review provides comprehensive information for an innovative supply way of terpene via microbial cell factory, which could facilitate the development and application of this technique at the industrial scale.

Fermentation Strategies for Production of Pharmaceutical Terpenoids in Engineered Yeast

Terpenoids, also known as isoprenoids, are a broad and diverse class of plant natural products with significant industrial and pharmaceutical importance. Many of these natural products have antitumor, anti-inflammatory, antibacterial, antiviral, and antimalarial effects, support transdermal absorption, prevent and treat cardiovascular diseases, and have hypoglycemic activities. Production of these compounds are generally carried out through extraction from their natural sources or chemical synthesis. However, these processes are generally unsustainable, produce low yield, and result in wasting of substantial resources, most of them limited. Microbial production of terpenoids provides a sustainable and environment-friendly alternative. In recent years, the yeast Saccharomyces cerevisiae has become a suitable cell factory for industrial terpenoid biosynthesis due to developments in omics studies (genomics, transcriptomics, metabolomics, proteomics), and mathematical modeling. Besides that, fermentation development has a significant importance on achieving high titer, yield, and productivity (TYP) of these compounds. Up to now, there have been many studies and reviews reporting metabolic strategies for terpene biosynthesis. However, fermentation strategies have not been yet comprehensively discussed in the literature. This review summarizes recent studies of recombinant production of pharmaceutically important terpenoids by engineered yeast, S. cerevisiae, with special focus on fermentation strategies to increase TYP in order to meet industrial demands to feed the pharmaceutical market. Factors affecting recombinant terpenoids production are reviewed (strain design and fermentation parameters) and types of fermentation process (batch, fed-batch, and continuous) are discussed.

Adaptive evolution of engineered yeast for squalene production improvement and its genome-wide analysis

In the present study, the adaptive evolution of a metabolically engineered Saccharomyces cerevisiae strain in the presence of an enzyme inhibitor terbinafine for enhanced squalene accumulation via serial transfer leads to the development of robust strains. After adaptation for nearly 1500 h, a strain with higher squalene production efficiency was identified at a specific growth rate of 0.28 h^-1 with a final squalene titer of 193 mg/L, which is 16.5-fold higher than the BY4741 and 3-fold higher over the metabolically engineered SK22 strain. Whole-genome sequencing comparison between the reference strain and the evolved variant SK23 has led to the identification of 462 single-nucleotide variants (SNVs) between both strains, with 102 SNVs affecting metabolism-related genes. It was also established that F420I mutation of ERG1 in S. cerevisiae improves squalene synthesis. Further, the effect of increased squalene on lipid droplet and neutral lipid pattern in the evolved mutant strains was investigated by fluorescent techniques proving that the neutral lipid content and clustering of lipid droplets increase with an increase in squalene.

Metabolic engineering of Yarrowia lipolytica for improving squalene production

The aim of this present research is to enhance the squalene production in Yarrowia lipolytica using pathway engineering and bioprocess engineering. Firstly, to improve the production of squalene, the endogenous HMG-CoA reductase (HMG1) was overexpressed in Y. lipolytica to yield 208.88 mg/L squalene. Secondly, the HMG1 and diacylglycerol acyltranferase (DGA1) were co-overexpressed, the derived recombinant Y. lipolytica SQ-1 strain produced 439.14 mg/L of squalene. Thirdly, by optimizing the fermentation medium, the improved titer of squalene with 514.34 mg/L was obtained by the engineered strain SQ-1 grown on YPD-80 medium. Finally, by optimizing the addition concentrations of acetate, citrate and terbinafine, the 731.18 mg/L squalene was produced in the engineered strain SQ-1 with the addition of 0.5 mg/L terbinafine. This work describes the highest reported squalene titer in Y. lipolytica to date. This study will provide the foundation for further engineering Y. lipolytica capable of cost-efficiently producing squalene.

Therapeutic Agents for the Treatment of Temporomandibular Joint Disorders: Progress and Perspective

Temporomandibular joint disorders (TMD) are a common health condition caused by the structural or functional disorders of masticatory muscles and the temporomandibular joint (TMJ). Abnormal mandibular movement in TMD patients may cause pain, chronic inflammation, and other discomfort, which could be relieved by a variety of drugs through various delivery systems. In this study, we summarized commonly used therapeutic agents in the management of TMD as well as novel bioactive molecules in preclinical stage and clinical trials. The emerging therapy strategies such as novel intra-TMJ delivery systems and implants based on tissue engineering are also discussed. This comprehensive review will strengthen our understanding of pharmacological approaches for TMD therapy.

Combinatorial Modulation of Linalool Synthase and Farnesyl Diphosphate Synthase for Linalool Overproduction in Saccharomyces cerevisiae

Linalool, as a fragrant monoterpene, is an important feedstock for food, pharmaceuticals, and cosmetics industries. Although our previous study had significantly increased linalool production by the directed evolution of linalool synthase and overexpression of the whole mevalonate pathway genes, the engineered yeast strain suffered from dramatically reduced biomass. Herein, a stress-free linalool-producing yeast cell factory was constructed by the combinational regulation of linalool synthase and farnesyl diphosphate synthase instead of multienzyme overexpression. First, the expression level of linalool synthase was successfully enhanced by introducing a N-terminal SKIK tag, which improved linalool production by 3.3-fold. Subsequently, the modular assembly of linalool synthase and dominant negative farnesyl diphosphate synthase via short peptide tags efficiently converted geranyl pyrophosphate to linalool. Additional downregulation of the native farnesyl diphosphate synthase led to the highest reported linalool production (80.9 mg/L) in yeast. This combinatorial modulation strategy may also be applied to the production of other high-value monoterpenes.

High-Level Production of Sesquiterpene Patchoulol in Saccharomyces cerevisiae

Patchoulol is a tricyclic sesquiterpene widely used in perfumes and cosmetics. Herein, comprehensive engineering strategies were employed to construct an efficient yeast strain for patchoulol production. First, a platform strain was constructed via pathway modification. Second, three off-pathway genes were deleted, which led to significant physiological changes in yeast. Further, strengthening of the ergosterol pathway, enhancement of the energy supply, and a decrease in intracellular reactive oxygen species were implemented to improve the physiological status of yeast, demonstrating a new promotive relationship between ergosterol biosynthesis and synthesis of patchoulol. Moreover, patchoulol synthase was improved through protein modification and Mg²⁺ addition, reaching a final titer of 141.5 mg/L in a shake flask. Finally, a two-stage fermentation with dodecane addition was employed to achieve the highest production (1632.0 mg/L, 87.0 mg/g dry cell weight, 233.1 mg/L/d) ever reported for patchoulol in a 5 L bioreactor. This work lays a foundation for green and efficient patchoulol production.

Improved production of germacrene A, a direct precursor of ß-elemene, in engineered Saccharomyces cerevisiae by expressing a cyanobacterial germacrene A synthase

Background

The sesquiterpene germacrene A is a direct precursor of ß-elemene that is a major component of the Chinese medicinal herb Curcuma wenyujin with prominent antitumor activity. The microbial platform for germacrene A production was previously established in Saccharomyces cerevisiae using the germacrene A synthase (LTC2) of Lactuca sativa.

Results

We evaluated the performance of LTC2 (LsGAS) as well as nine other identified or putative germacrene A synthases from different sources for the production of germacrene A. AvGAS, a synthase of Anabaena variabilis, was found to be the most efficient in germacrene A production in yeast. AvGAS expression alone in S. cerevisiae CEN.PK2-1D already resulted in a substantial production of germacrene A while LTC2 expression did not. Further metabolic engineering the yeast using known strategies including overexpression of tHMGR1 and repression of squalene synthesis pathway led to an 11-fold increase in germacrene A production. Site-directed mutagenesis of AvGAS revealed that while changes of several residues located within the active site cavity severely compromised germacrene A production, substitution of Phe23 located on the lateral surface with tryptophan or valine led to a 35.2% and 21.8% increase in germacrene A production, respectively. Finally, the highest production titer of germacrene A reached 309.8 mg/L in shake-flask batch culture.

Conclusions

Our study highlights the potential of applying bacterial sesquiterpene synthases with improved performance by mutagenesis engineering in producing germacrene A.

Metabolic engineering and synthetic biology for isoprenoid production in Escherichia coli and Saccharomyces cerevisiae

Isoprenoids, often called terpenoids, are the most abundant and highly diverse family of natural organic compounds. In plants, they play a distinct role in the form of photosynthetic pigments, hormones, electron carrier, structural components of membrane, and defence. Many isoprenoids have useful applications in the pharmaceutical, nutraceutical, and chemical industries. They are synthesized by various isoprenoid synthase enzymes by several consecutive steps. Recent advancement in metabolic engineering and synthetic biology has enabled the production of these isoprenoids in the heterologous host systems like Escherichia coli and Saccharomyces cerevisiae. Both heterologous systems have been engineered for large-scale production of value-added isoprenoids. This review article will provide the detailed description of various approaches used for engineering of methyl-D-erythritol-4-phosphate (MEP) and mevalonate (MVA) pathway for synthesizing isoprene units (C₅) and ultimate production of diverse isoprenoids. The review particularly highlighted the efforts taken for the production of C₅-C₂₀ isoprenoids by metabolic engineering techniques in E. coli and S. cerevisiae over a decade. The challenges and strategies are also discussed in detail for scale-up and engineering of isoprenoids in the heterologous host systems.Key points• Isoprenoids are beneficial and valuable natural products.• E. coli and S. cerevisiae are the promising host for isoprenoid biosynthesis.• Emerging techniques in synthetic biology enabled the improved production.• Need to expand the catalogue and scale-up of un-engineered isoprenoids. Metabolic engineering and synthetic biology for isoprenoid production in Escherichia coli and Saccharomyces cerevisiae.

Recent Advances on Feasible Strategies for Monoterpenoid Production in Saccharomyces cerevisiae

Terpenoids are a large diverse group of natural products which play important roles in plant metabolic activities. Monoterpenoids are the main components of plant essential oils and the active components of some traditional Chinese medicinal herbs. Some monoterpenoids are widely used in medicine, cosmetics and other industries, and they are mainly obtained by plant biomass extraction methods. These plant extraction methods have some problems, such as low efficiency, unstable quality, and high cost. Moreover, the monoterpenoid production from plant cannot satisfy the growing monoterpenoids demand. The development of metabolic engineering, protein engineering and synthetic biology provides an opportunity to produce large amounts of monoterpenoids eco-friendly using microbial cell factories. This mini-review covers current monoterpenoids production using Saccharomyces cerevisiae. The monoterpenoids biosynthetic pathways, engineering of key monoterpenoids biosynthetic enzymes, and current monoterpenoids production using S. cerevisiae were summarized. In the future, metabolically engineered S. cerevisiae may provide one possible green and sustainable strategy for monoterpenoids supply.

Synthetic biology, combinatorial biosynthesis, and chemo‑enzymatic synthesis of isoprenoids

Isoprenoids are a large class of natural products with myriad applications as bioactive and commercial compounds. Their diverse structures are derived from the biosynthetic assembly and tailoring of their scaffolds, ultimately constructed from two C5 hemiterpene building blocks. The modular logic of these platforms can be harnessed to improve titers of valuable isoprenoids in diverse hosts and to produce new-to-nature compounds. Often, this process is facilitated by the substrate or product promiscuity of the component enzymes, which can be leveraged to produce novel isoprenoids. To complement rational enhancements and even re-programming of isoprenoid biosynthesis, high-throughput approaches that rely on searching through large enzymatic libraries are being developed. This review summarizes recent advances and strategies related to isoprenoid synthetic biology, combinatorial biosynthesis, and chemo-enzymatic synthesis, focusing on the past 5 years. Emerging applications of cell-free biosynthesis and high-throughput tools are included that culminate in a discussion of the future outlook and perspective of isoprenoid biosynthetic engineering.