High-Level Production of Sesquiterpene Patchoulol in Saccharomyces cerevisiae

Efficient Plant Triterpenoids Synthesis in Saccharomyces cerevisiae: from Mechanisms to Engineering Strategies

Triterpenoids possess a range of biological activities and are extensively utilized in the pharmaceutical, food, cosmetic, and chemical industries. Traditionally, they are acquired through chemical synthesis and plant extraction. However, these methods have drawbacks, including high energy consumption, environmental pollution, and being time-consuming. Recently, the de novo synthesis of triterpenoids in microbial cell factories has been achieved. This represents a promising and environmentally friendly alternative to traditional supply methods. Saccharomyces cerevisiae, known for its robustness, safety, and ample precursor supply, stands out as an ideal candidate for triterpenoid biosynthesis. However, challenges persist in industrial production and economic feasibility of triterpenoid biosynthesis. Consequently, metabolic engineering approaches have been applied to improve the triterpenoid yield, leading to substantial progress. This review explores triterpenoids biosynthesis mechanisms in S. cerevisiae and strategies for efficient production. Finally, the review also discusses current challenges and proposes potential solutions, offering insights for future engineering.

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.

Catalytic Mechanism and Heterologous Biosynthesis Application of Sesquiterpene Synthases

Sesquiterpenes comprise a diverse group of natural products with a wide range of applications in cosmetics, food, medicine, agriculture, and biofuels. Heterologous biosynthesis is increasingly employed for sesquiterpene production, aiming to overcome the limitations associated with chemical synthesis and natural extraction. Sesquiterpene synthases (STSs) play a crucial role in the heterologous biosynthesis of sesquiterpene. Under the catalysis of STSs, over 300 skeletons are produced through various cyclization processes (C1-C10 closure, C1-C11 closure, C1-C6 closure, and C1-C7 closure), which are responsible for the diversity of sesquiterpenes. According to the cyclization types, we gave an overview of advances in understanding the mechanism of STSs cyclization from the aspects of protein crystal structures and site-directed mutagenesis. We also summarized the applications of engineering STSs in the heterologous biosynthesis of sesquiterpene. Finally, the bottlenecks and potential research directions related to the STSs cyclization mechanism and application of modified STSs were presented.

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.

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

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

PcENO3 interacts with patchoulol synthase to positively affect the enzymatic activity and patchoulol biosynthesis in Pogostemon cablin

Patchouli alcohol, a significant bioactive component of the herbal plant Pogostemon cablin, has considerable medicinal and commercial potential. Several genes and transcription factors involved in the biosynthesis pathway of patchouli alcohol have been identified. However, so far, regulatory factors directly interacting with patchouli synthase (PTS) have not been reported. This study was conducted to analyze the interaction between PcENO3 and PcPTS to explore the molecular regulation effect of PcENO3 on patchouli alcohol biosynthesis. PcENO3, a homologous protein of Arabidopsis ENO3 belonging to the enolase family, was identified and characterized. Subcellular localization experiments in Arabidopsis protoplast cells indicated that the PcENO3 protein was localized in both the cytoplasm and nucleus. The physical interaction between PcENO3 and PcPTS was confirmed through yeast two-hybrid (Y2H), GST pull-down, and bimolecular fluorescence complementation assays. Furthermore, the Y2H assay demonstrated that PcENO3 could also interact with JAZ proteins in the JA pathway. Enzymatic assays showed that the interaction with PcENO3 increased the catalytic activity of patchoulol synthase. Additionally, suppression of PcENO3 expression with VIGS (virus-induced gene silencing) decreased patchouli alcohol content compared to the control. These findings suggest that PcENO3 interacts with patchoulol synthase and modulates patchoulol biosynthesis by enhancing the enzymatic activity of PcPTS.

Enzyme and Metabolic Engineering Strategies for Biosynthesis of α-Farnesene in Saccharomyces cerevisiae

α-Farnesene, a type of acyclic sesquiterpene, is an important raw material in agriculture, aircraft fuel, and the chemical industry. In this study, we constructed an efficient α-farnesene-producing yeast cell factory by combining enzyme and metabolic engineering strategies. First, we screened different plants for α-farnesene synthase (AFS) with the best activity and found that AFS from Camellia sinensis (CsAFS) exhibited the most efficient α-farnesene production in Saccharomyces cerevisiae 4741. Second, the metabolic flux of the mevalonate pathway was increased to improve the supply of the precursor farnesyl pyrophosphate. Third, inducing site-directed mutagenesis in CsAFS, the CsAFSW281C variant was obtained, which considerably increased α-farnesene production. Fourth, the N-terminal serine-lysine-isoleucine-lysine (SKIK) tag was introduced to construct the SKIK∼CsAFSW281C variant, which further increased α-farnesene production to 2.8 g/L in shake-flask cultures. Finally, the α-farnesene titer of 28.3 g/L in S. cerevisiae was obtained by fed-batch fermentation in a 5 L bioreactor.

Switching carbon metabolic flux for enhancing the production of sesquiterpene-based high-density biofuel precursor in Saccharomyces cerevisiae

BACKGROUND

Sesquiterpenes are designated as a large class of plant-derived natural active compounds, which have wide applications in industries of energy, food, cosmetics, medicine and agriculture. Neither plant extraction nor chemical synthesis can meet the massive market demands and sustainable development goals. Biosynthesis in microbial cell factories represents an eco-friendly and high-efficient way. Among several microorganisms, Saccharomyces cerevisiae exhibited the potential as a chassis for bioproduction of various sesquiterpenes due to its native mevalonate pathway. However, its inefficient nature limits biosynthesis of diverse sesquiterpenes at industrial grade.

RESULTS

Herein, we exploited an artificial synthetic malonic acid-acetoacetyl-CoA (MAAC) metabolic pathway to switch central carbon metabolic flux for stable and efficient biosynthesis of sesquiterpene-based high-density biofuel precursor in S. cerevisiae. Through investigations at transcription and metabolism levels, we revealed that strains with rewired central metabolism can devote more sugars to β-caryophyllene production. By optimizing the MVA pathway, the yield of β-caryophyllene from YQ-4 was 25.8 mg/L, which was 3 times higher than that of the initial strain YQ-1. Strain YQ-7 was obtained by introducing malonic acid metabolic pathway. Combing the optimized flask fermentation process, the target production boosted by about 13-fold, to 328 mg/L compared to that in the strain YQ-4 without malonic acid metabolic pathway.

CONCLUSION

This designed MAAC pathway for sesquiterpene-based high-density biofuel precursor synthesis can provide an impressive cornerstone for achieving a sustainable production of renewable fuels.

Regulation of Ethanol Assimilation for Efficient Accumulation of Squalene in Saccharomyces cerevisiae

Squalene is a triterpene that can be obtained from fish and plant oils. It is important in cosmetics and vaccines and is a precursor for many high-value terpenes and steroids. In order to increase squalene accumulation, the mevalonate pathway was systematically enhanced. Accumulation of squalene tended to increase when ethanol was added as a carbon source during fermentation, but a high concentration of ethanol affected both the strain growth and accumulation of products. By overexpressing the key trehalose synthesis gene TPS1 and the heat shock protein gene HSP104, the content of trehalose by Saccharomyces cerevisiae (S. cerevisiae) was enhanced, and stress caused by ethanol was relieved. The OD₆₀₀ value of the modified S. cerevisiae strain was increased by 80.2%, its ethanol tolerance was increased to 30 g/L, and it retained excellent activity with 50 g/L ethanol. After optimizing the fermentation conditions, the squalene titer in a 5 L bioreactor reached 27.3 g/L and the squalene content was 650 mg/g dry cell weight, the highest squalene production parameters reported to date for a microorganism.

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

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

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.

Candida glycerinogenes-Promoted α-Pinene and Squalene Co-production Strategy Based on α-Pinene Stress

α-Pinene is a naturally occurring monoterpene, which is widely used in fragrances, cosmetics, and foods. Due to the high cellular toxicity of α-pinene, this work considered the application of Candida glycerinogenes, an effective industrial strain with high resistance, in α-pinene synthesis. It was found that α-pinene-induced stress resulted in an intracellular accumulation of reactive oxygen species with an increased formation of squalene as a cytoprotective compound. As squalene is a downstream product in the mevalonate (MVA) pathway for α-pinene synthesis, a strategy based on the promotion of α-pinene and squalene co-production under α-pinene stress is proposed. By introducing the α-pinene synthesis pathway and enhancing the MVA pathway, the production of both α-pinene and squalene is increased. We have demonstrated that intracellular synthesis of α-pinene is effective in promoting squalene synthesis. The generation of intercellular reactive oxygen that accompanies α-pinene synthesis promotes squalene synthesis with a resultant cellular protection and upregulation of MVA pathway genes that facilitate α-pinene production. In addition, we have overexpressed phosphatase and introduced NPP as a substrate to synthesize α-pinene, where co-dependent fermentation yielded 208 mg/L squalene and 12.8 mg/L α-pinene. This work establishes a viable strategy to promote terpene-co-dependent fermentation based on stress.

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.

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.

Engineering Saccharomyces cerevisiae for enhanced (-)-α-bisabolol production

(-)-α-Bisabolol is naturally occurring in many plants and has great potential in health products and pharmaceuticals. However, the current extraction method from natural plants is unsustainable and cannot fulfil the increasing requirement. This study aimed to develop a sustainable strategy to enhance the biosynthesis of (-)-α-bisabolol by metabolic engineering. By introducing the heterologous gene MrBBS and weakening the competitive pathway gene ERG9, a de novo (-)-α-bisabolol biosynthesis strain was constructed that could produce 221.96 mg/L (-)-α-bisabolol. Two key genes for (-)-α-bisabolol biosynthesis, ERG20 and MrBBS, were fused by a flexible linker (GGGS)₃ under the GAL7 promoter control, and the titer was increased by 2.9-fold. Optimization of the mevalonic acid pathway and multi-copy integration further increased (-)-α-bisabolol production. To promote product efflux, overexpression of PDR15 led to an increase in extracellular production. Combined with the optimal strategy, (-)-α-bisabolol production in a 5 L bioreactor reached 7.02 g/L, which is the highest titer reported in yeast to date. This work provides a reference for the efficient production of (-)-α-bisabolol in yeast.

High-yield production of protopanaxadiol from sugarcane molasses by metabolically engineered Saccharomyces cerevisiae

Background

Ginsenosides are Panax plant-derived triterpenoid with wide applications in cardiovascular protection and immunity-boosting. However, the saponins content of Panax plants is fairly low, making it time-consuming and unsustainable by direct extraction. Protopanaxadiol (PPD) is a common precursor of dammarane-type saponins, and its sufficient supply is necessary for the efficient synthesis of ginsenoside.

Results

In this study, a combinational strategy was used for the construction of an efficient yeast cell factory for PPD production. Firstly, a PPD-producing strain was successfully constructed by modular engineering in Saccharomyces cerevisiae BY4742 at the multi-copy sites. Then, the INO2 gene, encoding a transcriptional activator of the phospholipid biosynthesis, was fine-tuned to promote the endoplasmic reticulum (ER) proliferation and improve the catalytic efficiency of ER-localized enzymes. To increase the metabolic flux of PPD, dynamic control, based on a carbon-source regulated promoter P_HXT1, was introduced to repress the competition of sterols. Furthermore, the global transcription factor UPC2-1 was introduced to sterol homeostasis and up-regulate the MVA pathway, and the resulting strain BY-V achieved a PPD production of 78.13 ± 0.38 mg/g DCW (563.60 ± 1.65 mg/L). Finally, sugarcane molasses was used as an inexpensive substrate for the first time in PPD synthesis. The PPD titers reached 1.55 ± 0.02 and 15.88 ± 0.65 g/L in shake flasks and a 5-L bioreactor, respectively. To the best of our knowledge, these results were new records on PPD production.

Conclusion

The high-level of PPD production in this study and the successful comprehensive utilization of low-cost carbon source -sugarcane molassesindicate that the constructed yeast cell factory is an excellent candidate strain for the production of high-value-added PPD and its derivativeswith great industrial potential.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01949-4.

Enhancement of linalool production in Saccharomyces cerevisiae by utilizing isopentenol utilization pathway

BACKGROUND

Linalool is a monoterpenoid, also a vital silvichemical with commercial applications in cosmetics, flavoring ingredients, and medicines. Regulation of mevalonate (MVA) pathway metabolic flux is a common strategy to engineer Saccharomyces cerevisiae for efficient linalool production. However, metabolic regulation of the MVA pathway is complex and involves competition for central carbon metabolism, resulting in limited contents of target metabolites.

RESULTS

In this study, first, a truncated linalool synthase (t26AaLS1) from Actinidia arguta was selected for the production of linalool in S. cerevisiae. To simplify the complexity of the metabolic regulation of the MVA pathway and increase the flux of isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP), we introduced the two-step isopentenyl utilization pathway (IUP) into S. cerevisiae, which could produce large amounts of IPP/DMAPP. Further, the S. cerevisiae IDI1 (ecoding isopentenyl diphosphate delta-isomerase) and ERG20^F96W-N127W (encoding farnesyl diphosphate synthase) genes were integrated into the yeast genome, combined with the strategies of copy number variation of the t26AaLS1 and ERG20^F96W-N127W genes to increase the metabolic flux of the downstream IPP, as well as optimization of isoprenol and prenol concentrations, resulting in a 4.8-fold increase in the linalool titer. Eventually, under the optimization of carbon sources and Mg²⁺ addition, a maximum linalool titer of 142.88 mg/L was obtained in the two-phase extractive shake flask fermentation.

CONCLUSIONS

The results show that the efficient synthesis of linalool in S. cerevisiae could be achieved through a two-step pathway, gene expression adjustment, and optimization of culture conditions. The study may provide a valuable reference for the other monoterpenoid production in S. cerevisiae.

Reengineering of 7-dehydrocholesterol biosynthesis in Saccharomyces cerevisiae using combined pathway and organelle strategies

7-Dehydrocholesterol (7-DHC) is a widely used sterol and a precursor of several costly steroidal drugs. In this study, 7-DHC biosynthesis pathway was constructed and modified in Saccharomyces cerevisiae. Firstly, the biosynthesis pathway was constructed by knocking out the competitive pathway genes ERG5 and ERG6 and integrating two DHCR24 copies from Gallus gallus at both sites. Then, 7-DHC titer was improved by knocking out MOT3, which encoded a transcriptional repressor for the 7-DHC biosynthesis pathway. Next, by knocking out NEM1 and PAH1, 7-DHC accumulation was improved, and genes upregulation was verified by quantitative PCR (qPCR). Additionally, tHMG1, IDI1, ERG2, ERG3, DHCR24, POS5, and CTT1 integration into multi-copy sites was used to convert precursors to 7-DHC, and increase metabolic flux. Finally, qPCR confirmed the significant up-regulation of key genes transcriptional levels. In a 96 h shaker flask fermentation, the 7-DHC titer was 649.5 mg/L by de novo synthesis. In a 5 L bioreactor, the 7-DHC titer was 2.0 g/L, which was the highest 7-DHC titer reported to date. Our study is of great significance for the industrial production of 7-DHC and steroid development for medical settings.

Glycosylation Modification Enhances (2S)-Naringenin Production in Saccharomyces cerevisiae

(2S)-Naringenin is an important flavonoid precursor, with multiple nutritional and pharmacological activities. Both (2S)-naringenin and other flavonoid production are hindered by poor water solubility and inhibited cell growth. To address this, we increased solubility and improved cell growth by partially glycosylating (2S)-naringenin to naringenin-7-O-glucoside, which facilitated increased extracellular secretion, by knocking out endogenous glycosyl hydrolase genes, EXG1 and SPR1, and expressing the glycosyltransferase gene (UGT733C6). Naringenin-7-O-glucoside synthesis was further improved by optimizing UDP-glucose and shikimate pathways. Then, hydrochloric acid was used to hydrolyze naringenin-7-O-glucoside to (2S)-naringenin outside the cell. Thus, our optimized Saccharomyces cerevisiae strain E32T19 produced 1184.1 mg/L (2S)-naringenin, a 7.9-fold increase on the starting strain. Therefore. we propose that glycosylation modification is a useful strategy for the efficient heterologous biosynthesis of (2S)-naringenin in S. cerevisiae.

De novo biosynthesis of τ-cadinol in engineered Escherichia coli

τ-Cadinol is a sesquiterpene that is widely used in perfume, fine chemicals and medicines industry. In this study, we established a biosynthetic pathway for the first time in engineered Escherichia coli for production of τ-cadinol from simple carbon sources. Subsequently, we further improved the τ-cadinol production to 35.9 ± 4.3 mg/L by optimizing biosynthetic pathway and overproduction of rate-limiting enzyme IdI. Finally, the titer was increased to 133.5 ± 11.2 mg/L with a two-phase organic overlay-culture medium system. This study shows an efficient method for the biosynthesis of τ-cadinol in E. coli with the heterologous hybrid MVA pathway.

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.

Secretory Production of Tocotrienols in Saccharomyces cerevisiae

Tocotrienols as important components of vitamin E have attracted increasing attention, with recent progress made in their heterologous biosynthesis, but all as intracellular products. Aiming to further improve the tocotrienol production capacity of engineered yeast and to advance toward industrial fermentation of tocotrienols, we first optimized the synthetic pathway to enhance the tocotrienol yield and then attempted to realize their secretory production by exploring biphasic extractive fermentation conditions and screening for endogenous transporters. Finally, a Saccharomyces cerevisiae strain with tocotrienol yield of 25.57 mg/g dry cell weight was generated, and the tocotrienol titer reached 82.68 mg/L in shake-flask cultures, with 73.66% of the product secreted into the organic phase. For the first time, we have reported that the vitamin E components could be harvested as extracellular products of microbial cell factories, which could largely simplify the downstream process and could be of significance for fermentative production of these products.

Recent advances in construction and regulation of yeast cell factories

The past decade has witnessed the rapid progress in development of synthetic biology, and advances in construction of yeast cell factories open vast opportunities for green and sustainable production of chemicals. Focusing on the progress in yeast engineering for production of plant natural products in the last 5 years, this review introduces different yeast chassis used for cell factory construction, including Saccharomyces cerevisiae, Yarrowia lipolytica and Komagataella phaffii, together with the emerging genome editing tools. The metabolic regulation strategies developed for yeast engineering are highlighted, such as subcellular pathway localization dynamic regulation, and transporter engineering. C1-based chemical bioproduction by engineered yeast is also covered. Finally, the existing challenges and future prospects in creating efficient yeast cell factories are summarized.

Systematic identification of Ocimum sanctum sesquiterpenoid synthases and (-)-eremophilene overproduction in engineered yeast

Plant-derived natural active products have attracted increasing attention for use in flavors and perfumes. These compounds also have applications in insect pest control because of their environment-friendly properties. Holy basil (Ocimum sanctum), a famous herb used in Ayurveda in India, is a natural source of medical healing agents and insecticidal repellents. Despite the available genomic sequences and genome-wide bioinformatic analysis of terpene synthase genes, the functionality of the sesquiterpene genes involved in the unique fragrance and insecticidal activities of Holy basil are largely unknown. In this study, we systematically screened the sesquiterpenoid biosynthesis genes in this plant using a precursor-providing yeast system. The enzymes that synthesize β-caryophyllene and its close isomer α-humulene were successfully identified. The enzymatic product of OsaTPS07 was characterized by in vivo mining, in vitro reaction, and NMR detection. This product was revealed as (-)-eremophilene. We created a mutant yeast strain that can achieve a high-yield titer by adjusting the gene copy number and FPP precursor enhancement. An optimized two-stage fed-batch fermentation method achieved high biosynthetic capacity, with a titer of 34.6 g/L cyclic sesquiterpene bioproduction in a 15-L bioreactor. Further insect-repelling assays demonstrated that (-)-eremophilene repelled the insect pest, fall leafworm, suggesting the potential of (-)-eremophilene as an alternative to synthetic chemicals for agricultural pest control. This study highlights the potential of our microbial platform for the bulk mining of plant-derived ingredients and provides an impressive cornerstone for their industrial utilization.

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.

Engineering Plant Sesquiterpene Synthesis into Yeasts: A Review

Sesquiterpenes are natural compounds composed of three isoprene units. They represent the largest class of terpene compounds found in plants, and many have remarkable biological activities. Furthermore, sesquiterpenes have broad applications in the flavor, pharmaceutical and biofuel industries due to their complex structures. With the development of metabolic engineering and synthetic biology, the production of different sesquiterpenes has been realized in various chassis microbes. The microbial production of sesquiterpenes provides a promising alternative to plant extraction and chemical synthesis, enabling us to meet the increasing market demand. In this review, we summarized the heterologous production of different plant sesquiterpenes using the eukaryotic yeasts Saccharomyces cerevisiae and Yarrowia lipolytica, followed by a discussion of common metabolic engineering strategies used in this field.

Enhancement of Patchoulol Production in Escherichia coli via Multiple Engineering Strategies

As a natural sesquiterpene compound with numerous biological activities, patchoulol has extensive applications in the cosmetic industry and potential usage in pharmaceuticals. Although several patchoulol-producing microbial strains have been constructed, the low productivity still hampers large-scale fermentation. Escherichia coli possesses the ease of genetic manipulation and simple nutritional requirements and does not comprise competing pathways for the farnesyl diphosphate (FPP) precursor, showing its potential for patchoulol biosynthesis. Here, combinatorial strategies were applied to produce patchoulol in E. coli. The initial strain was constructed, and it produced 14 mg/L patchoulol after fermentation optimization. Patchoulol synthase (PTS) was engineered by semirational design, resulting in improved substrate binding affinity and a patchoulol titer of 40.3 mg/L; the patchoulol titer reached 66.2 mg/L after fusing of PTS with FPP synthase. To further improve the patchoulol production, the genome of an efficient chassis strain was engineered by deleting the competitive routes for acetate, lactate, ethanol, and succinate synthesis and cumulatively enhancing the expression of efflux transporters, which improved patchoulol production to 338.6 mg/L. When tested in a bioreactor, the patchoulol titer and productivity were further improved to 970.1 mg/L and 199 mg/L/d, respectively, and were among the highest levels reported using mineral salt medium.