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

Exploration and mutagenesis of the germacrene A synthase from Solidago canadensis to enhance germacrene A production in E. coli

β-elemene is an effective anti-cancer component which has been widely used in clinic. However, it still relies on the extraction from the Chinese medicine plant Curcuma wenyujin, which seriously limits its application. Synthetic biology offers a promising approach to satisfy its supply. β-elemene is derived from germacrene A (GA), which is synthesized by germacrene A synthase (GAS), through Cope rearrangement under heat condition instead of enzymatic reaction. In this study, an effective germacrene A synthase (ScGAS) was identified from Solidago canadensis which could produce GA when expressed in E. coli. By introducing the heterogeneous MVA pathway to enrich the FPP pool, the strain yielded 147 mg/L of GA in shake flasks which represented 2.98-fold improvement over the initial one. Moreover, combining molecular docking with phylogeny analysis of ScGAS largely narrowed down the category of its key residues' mutagenesis. The Y376L mutant showed the highest yield of 487 mg/L which was almost 10-fold higher than the initial yield. These results indicate that diverting the metabolism of the host and enzyme mutagenesis based on the combination of molecular docking and phylogeny analysis are of great value to constructing terpenoids chassis.

Combinatorial metabolic engineering of Yarrowia lipolytica for high-level production of the plant-derived diterpenoid sclareol

BACKGROUND

Sclareol, a diterpene alcohol derived from Salvia sclarea, is primarily used in the synthesis of ambrox, an alternative to the expensive spice ambergris. However, commercial production of sclareol from plant extraction is costly and environmentally problematic, limiting its scalability. Recent advances in synthetic biology have enabled the construction of efficient cell factories for sclareol synthesis, offering a more sustainable solution.

RESULTS

In this study, we engineered Yarrowia lipolytica to produce sclareol by integrating genes encoding (13E)-8α-hydroxylabden-15-yl diphosphate synthase (LPPS) and sclareol synthase (SCS). Sclareol titers were further enhanced through the fusion of SsSCS and SsLPPS proteins, as well as multi-copy gene integration. To increase the precursor geranylgeranyl diphosphate (GGPP), we overexpressed various geranylgeranyl diphosphate synthases (GGS1), resulting in significant accumulation of GGPP. Additionally, optimization of the mevalonate pathway, coupled with the downregulation of lipid synthesis and upregulation of lipid degradation, directed more acetyl CoA towards sclareol production.

CONCLUSIONS

In this study, we reprogrammed the metabolism of Y. lipolytica by combinatorial metabolic engineering with a sclareol titer of 2656.20 ± 91.30 mg/L in shake flasks. Our findings provide a viable strategy for utilizing Y. lipolytica as a microbial cell factory to produce sclareol.

Synthetic Engineering of Microbes for Production of Terpenoid Food Ingredients

Terpenoids are a class of chemicals comprising many food ingredient chemicals. Synthetic biology and metabolic engineering have been performed to produce microbial cell factories for their production. For improved production of various terpenoid ingredients, heterologous synthetic pathways can be optimized at multiple dimensions. Optimizing chassis precursor supply and overcoming the host's inherent metabolic rigidity are crucial for enhancing overall efficiency of heterologous terpenoid production. Integrating synthetic regulatory circuits can facilitate the staged programming and precise optimization of heterologous and endogenous metabolism. Engineering long-term genetic and metabolic stability is essential for the successful scale-up of commercial production. Maximizing efficiency in food terpenoid production will rely on interdisciplinary synthetic and engineering biology tools to advance state-of-the-art capabilities for the streamlined design and construction of complex genotypes in microbial chassis.

Reconstructing Candida glycerinogenes Metabolism to Efficiently Synthesize (-)-α-Bisabolol

(-)-α-Bisabolol is one of the important derivatives in the mevalonate (MVA) pathway. Yeast not only possesses a complete MVA metabolic pathway but also has mature modification and optimization strategies, among which transcription factor regulation is a very effective method. In this study, by screening transcription factors associated with the MVA pathway, a new regulatory factor, ECM22, was discovered that can be used for terpenoid synthesis, and ECM22 proved to be the most effective compared to other screened transcription factors. Previous studies have indicated that ECM22 is related to sterol synthesis, as it enters the nucleus through its N-terminal domain to recognize and bind to sterol regulatory elements (SREs) on promoters, thereby activating the transcriptional activity of target genes. Based on the characteristics of this transcription factor, we achieved fine-tuning of (-)-α-bisabolol synthesis by optimizing sterol elements and varying sterol content, resulting in a 280% diversion of carbon flux toward (-)-α-bisabolol synthesis. This is the first time ECM22 has been utilized in the terpenoid synthesis process, allocating the largest metabolic flux to the synthesis pathway of terpenoids. Ultimately, we obtained 1442.22 mg/L of (-)-α-bisabolol through fed-batch fermentation in a 5 L bioreactor, advancing the precise directional regulation of terpenoid metabolic engineering.

Construction of Saccharomyces cerevisiae Platform Strain for the Biosynthesis of Carotenoids and Apocarotenoids

Carotenoids and apocarotenoids, natural compounds with vital biological functions, are now sustainably produced via microbial synthesis as an eco-friendly alternative to inefficient and polluting traditional plant-based extraction methods. In their biosynthesis, β-carotene (BC) plays a crucial role as it is the key intermediate from which different downstream derivatives are formed. Here, we engineered a high-producing Saccharomyces cerevisiae platform strain to produce BC through a combination of systematic metabolic engineering and atmospheric and room temperature plasma mutagenesis. The strain achieved a BC production of 2.09 g/L via fed-batch fermentation in a 5-L bioreactor, the highest yield reported in S. cerevisiae to date. Using this platform strain, we constructed zeaxanthin- and β-ionone-producing strains by introducing key enzyme genes. The engineered strains produced 39.09 mg/L of zeaxanthin and 31.87 mg/L of β-ionone in shake-flask cultures. The engineered BC platform established in this study provides a higher starting point for producing diverse BC derivatives.

Engineering a Yeast Cell Factory to Sustainably Biosynthesize Parthenolide

The sesquiterpene lactone parthenolide is a promising anticancer drug. Its biosynthesis via a microbial cell factory has been considered as a sustainable alternative to plant extraction. Herein, systematic metabolic engineering approaches, as well as the introduction of a novel noncanonical tricarboxylic acid (TCA) cycle, were employed to enhance the production of the key precursor germacrene A. By identifying two new dehydrogenases and controlling the expression of parthenolide synthase, we further achieved the elimination of byproducts and enhanced parthenolide production. A two-stage fermentation approach and in situ product extraction using macroreticular resin were further applied to relieve the nocuous effect of costunolide and parthenolide on the growth of yeast cell factories, ultimately achieving a titer of 549.7 mg/L for parthenolide and 972.7 mg/L for costunolide in a 10 L fermenter, which represents the highest reported titer obtained by microbial fermentation. The strategies should also contribute to the microbial cell factory-construction for other natural products exhibiting toxicity.

Bioengineered yeast for preventing age-related diseases

The aging process entails a multifaceted decline in the capacity to restore homeostasis in response to stress. A prevalent characteristic of many age-related diseases is the presence of low-grade chronic inflammation, a risk factor contributing significantly to morbidity and mortality in the elderly population. Specific lifestyle interventions, such as regular physical activity, targeted diet, and supplementation, can delay the accumulation of chronic age-associated conditions by mitigating inflammation processes. Bioengineered yeast-producing compounds with distinctive bioactivities, including anti-inflammatory properties, have the potential to provide rich dietary alternatives for the prevention of age-related diseases. This review highlights recent achievements in engineering effective yeast platforms, namely Saccharomyces cerevisiae and Yarrowia lipolytica, that hold promise in retarding the onset of aging and age-related ailments.

Enhancing Cannabichromenic Acid Biosynthesis in Saccharomyces cerevisiae

Cannabichromene (CBC), a valuable but extremely low-abundance component of cannabinoids in Cannabis sativa L., is known for its ability to promote neurogenesis. The scarcity of CBC in natural C. sativa is primarily attributed to the inefficiency of the 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol 4 phosphate (DOXP/MEP) and fatty acid metabolism pathways, along with the limited competitive advantage of cannabichromenic acid synthetase (CBCAS) compared to other cannabinoid synthases. In this study, we constructed Saccharomyces cerevisiae capable of biosynthesizing cannabichromenic acid (CBCA) from glucose and olivetolic acid. First, we enhanced the supply of the precursor isopentenyl diphosphate/dimethylallyl diphosphate by introducing a two-step isopentenol utilization pathway (IUP). Additionally, we increased the CBCA titer by co-overexpressing endoplasmic reticulum auxiliary protein genes. Moreover, we improved the selectivity and catalytic activity of CBCAS through rational design. By localizing the IUP to peroxisomes, geranylgeranyl pyrophosphate and CBCA titers were further increased by 1.6-fold and 28%, respectively. Notably, the yeast strain synthesized CBCA at a rate 25.8% higher than that of C. sativa. Our findings suggest that microbial synthesis offers a promising alternative to traditional C. sativa for sustainable CBCA production.

Biosynthesis of Edible Terpenoids: Hosts and Applications

Microbial foods include microbial biomass, naturally fermented foods, and heterologously synthesized food ingredients derived from microbial fermentation. Terpenoids, using isoprene as the basic structure, possess various skeletons and functional groups. They exhibit diverse physicochemical properties and physiological activities, such as unique flavor, anti-bacterial, anti-oxidant, anti-cancer, and hypolipemic, making them extensively used in the food industry, such as flavor, fragrance, preservatives, dietary supplements, and medicinal health food. Compared to traditional strategies like direct extraction from natural species and chemical synthesis, microbial cell factories for edible terpenoids have higher titers and yields. They can utilize low-cost raw materials and are easily scaling-up, representing a novel green and sustainable production mode. In this review, we briefly introduce the synthetic pathway of terpenoids and the applications of microbial cell factories producing edible terpenoids. Secondly, we highlight several typical and non-typical microbial chassis in edible terpenoid-producing cell factories. In addition, we reviewed the recent advances of representative terpenoid microbial cell factories with a gram-scale titer in food flavor, food preservation, nutritional enhancers, and medicinal health foods. Finally, we predict the future directions of microbial cell factories for edible terpenoids and their commercialization process.

Improved biosynthesis of tyrosol by epigenetic modification-based regulation and metabolic engineering in Saccharomyces cerevisiae

Aromatic amino acids and their derivatives are high value chemicals widely used in food, pharmaceutical and feed industries. Current preparation methods for aromatic amino acid products are fraught with limitations. In this study, the efficient biosynthesis of aromatic amino acid compound tyrosol was investigated by epigenetic modification-based regulation and optimization of the biosynthetic pathway of aromatic amino acids. The production of tyrosol was significantly improved by the overexpression of m6A modification writer Ime4 and reader Pho92, and the positive regulator Gcr2. Introduction of Bbxfpk and deletion of Gpp1 further improved tyrosol production. Then the feedback inhibition of the shikimate pathway was relieved by the mutants Aro4K229L and Aro7G141S. The final tyrosol producing engineered strain was constructed by the deletion of PHA2, replacement of the native promoter of ARO10 with the strong promoter PGK1p, and introduction of tyrosine decarboxylase PcAAS. In the background of m6A modification regulation, this strain ultimately produced 954.69 ± 43.72 mg/L of tyrosol, promoted by 61.7-fold in shake-flask fermentation.

Herbal Multiomics Provide Insights into Gene Discovery and Bioproduction of Triterpenoids by Engineered Microbes

Triterpenoids are natural products found in plants that exhibit industrial and agricultural importance. Triterpenoids are typically synthesized through two main pathways: the mevalonate (MVA) and methylerythritol 4-phosphate (MEP) pathways. They then undergo structural diversification with the help of squalene cyclases (OSCs), cytochrome P450 monooxygenases (P450s), UDP glycosyltransferases (UGTs), and acyltransferases (ATs). Advances in multiomics technologies for herbal plants have led to the identification of novel triterpenoid biosynthetic pathways. The application of various analytical techniques facilitates the qualitative and quantitative analysis of triterpenoids. Progress in synthetic biology and metabolic engineering has also facilitated the heterologous production of triterpenoids in microorganisms, such as Escherichia coli and Saccharomyces cerevisiae. This review summarizes recent advances in biotechnological approaches aimed at elucidating the complex pathway of triterpenoid biosynthesis. It also discusses the metabolic engineering strategies employed to increase the level of triterpenoid production in chassis cells.

Yeast metabolism adaptation for efficient terpenoids synthesis via isopentenol utilization

Microbial biosynthesis has become the leading commercial approach for large-scale production of terpenoids, a valuable class of natural products. Enhancing terpenoid production, however, requires complex modifications on the host organism. Recently, a two-step isopentenol utilization (IU) pathway relying solely on ATP as the cofactor has been proposed as an alternative to the mevalonate (MVA) pathway, streamlining the synthesis of the common terpenoid precursors. Herein, we find that isopentenol inhibits energy metabolism, leading to reduced efficiency of the IU pathway in Saccharomyces cerevisiae. To overcome this, we engineer an IU pathway-dependent (IUPD) strain, designed for growth-coupled production. The IUPD strain is compelled to enhance the ATP supply, essential for the IU pathway, and incorporates a high-throughput screening method for enzyme evolution. The refined IU pathway surpasses the MVA pathway in synthesizing complex terpenoids. Our work offers valuable insights into developing growth-coupled strains adapted to efficient natural product synthesis.

Ogataea polymorpha as a next-generation chassis for industrial biotechnology

Ogataea (Hansenula) polymorpha is a nonconventional yeast with some unique characteristics, including fast growth, thermostability, and broad substrate spectrum. Other than common applications for protein production, O. polymorpha is attracting interest for chemical and protein production from methanol; a promising feedstock for the next-generation biomanufacturing due to its abundant sources and excellent characteristics. Benefiting from the development of synthetic biology, it has been engineered to produce value-added chemicals by extensively rewiring cellular metabolism. This Review discusses recently developed synthetic biology tools of O. polymorpha. The advances of chemicals production and systems biology were reviewed comprehensively. Finally, we look ahead to the developments of biomanufacturing in O. polymorpha to make an overall understanding of this chassis for academia and industry.

Screening and modification of (+)-germacrene A synthase for the production of the anti-tumor drug (-)-β-elemene in engineered Saccharomyces cerevisiae

(-)-β-Elemene is a primary bioactive compound derived from Curcuma wenyujin and has been widely utilized as an anti-tumor agent for various types of cancer. Due to the inefficiency of plant extraction methods for β-elemene, significant efforts have been directed toward the heterogeneous biosynthesis of β-elemene using microbial cell factories. However, there has been less emphasis on the stereochemical configuration of germacrene A and its rearranged product, β-elemene. In this study, we constructed a yeast cell factory to produce (-)-β-elemene by optimizing the mevalonate pathway and screening for germacrene A synthases (GASs) from both plant and microbial sources. Notably, we discovered that the rearranged products of GASs exhibited different conformations, and only (+)-germacrene A produced by plant-derived GASs could rearrange to form (-)-β-elemene. Building on this discovery, we further investigated the catalytic mechanisms of GASs and developed an efficient catalytic gene module for generating (+)-germacrene A. Ultimately, the engineered yeast produced 1152 mg/L of (-)-β-elemene, marking the highest titer reported in yeast to date. Overall, this work highlights the differences in the stereoconformations of catalytic products between plant- and microbial-derived germacrene A synthases and establishes a foundation for the green and efficient production of β-elemene with a specific stereochemical configuration.

Molecular and biochemical basis of interspecific variations in the organ-specific synthesis of floral terpenes between the domesticated cultivars and their wild relatives in Chrysanthemum

Terpenoids, as the main components of the floral scent, exhibit interspecific variations and spatial specificity in Chrysanthemum genus. Here, we selected two primary species as the ancestors of C. morifolium along with two classic cultivars to investigate the influence of domestication on the variations in emission and production of floral terpenoids. The results indicated that the wild relatives emitted and accumulated higher levels of terpenoids in their disc florets and phyllaries & receptacles compared to the cultivars. Six gene modules associated with terpenoid production in three floral organs were characterized through WGCNA. Furthermore, 28 terpene synthase (TPS) genes were identified from both wild relatives and cultivars by comparative transcriptome database. In vitro enzymatic activity assay revealed that several products of monoterpenoids (α-pinene and α-terpinene) and sesquiterpenoids (β-farnesene, α-copaene and γ-curcumene), were commonly catalyzed by TPSs identified from wild relatives and cultivars. Nevertheless, we found that β-myrcene, β-elemene, β-cadinene and β-caryophyllene were predominantly produced by TPSs in the wild relatives, while d-limonene and β-copaene were specifically catalyzed by TPSs in the cultivars. It was also observed that the expression of the CiLSTPS3 gene could be associated with the emission and accumulation of β-caryophyllene in floral scent. Overall, the complex biochemical functions of TPSs, along with their varying expression patterns, significantly contribute to the interspecific variations of floral terpenoids in the Chrysanthemum genus. Our findings provide new insights into the molecular and biochemical mechanisms underlying the impact of domestication on the production of floral terpenoids in Chrysanthemum.

Dynamically Regulating Homologous Recombination Enables Precise Genome Editing in Ogataea polymorpha

Methylotrophic yeast Ogataea polymorpha has become a promising cell factory due to its efficient utilization of methanol to produce high value-added chemicals. However, the low homologous recombination (HR) efficiency in O. polymorpha greatly hinders extensive metabolic engineering for industrial applications. Overexpression of HR-related genes successfully improved HR efficiency, which however brought cellular stress and reduced chemical production due to constitutive expression of the HR-related gene. Here, we engineered an HR repair pathway using the dynamically regulated gene ScRAD51 under the control of the l-rhamnose-induced promoter PLRA3 based on the previously constructed CRISPR-Cas9 system in O. polymorpha. Under the optimal inducible conditions, the appropriate expression level of ScRAD51 achieved up to 60% of HR rates without any detectable influence on cell growth in methanol, which was 10-fold higher than that of the wild-type strain. While adopting as the chassis strain for bioproductions, the dynamically regulated recombination system had 50% higher titers of fatty alcohols than that static regulation system. Therefore, this study provided a feasible platform in O. polymorpha for convenient genetic manipulation without perturbing cellular fitness.

Advances in metabolic engineering for enhanced acetyl-CoA availability in yeast

Acetyl-CoA is an intermediate metabolite in cellular central metabolism. It's a precursor for various valuable commercial products, including: terpenoids, fatty acids, and polyketides. With the advancement of metabolic and synthetic biology tools, microbial cell factories have been constructed for the efficient synthesis of acetyl-CoA and derivatives, with the Saccharomyces cerevisiae and Yarrowia lipolytica as two prominent chassis. This review summarized the recent developments in the biosynthetic pathways and metabolic engineering approaches for acetyl-CoA and its derivatives synthesis in these two yeasts. First, the metabolic routes involved in the biosynthesis of acetyl-CoA and derived products were outlined. Then, the advancements in metabolic engineering strategies for channeling acetyl-CoA toward the desired products were summarized, with particular emphasis on: enhancing metabolic flux in different organelles, refining precursor CoA synthesis, optimizing substrate utilization, and modifying protein acetylation level. Finally, future developments in advancing the metabolic engineering strategies for acetyl-CoA and related derivatives synthesis, including: reducing CO2 emissions, dynamically regulating metabolic pathways, and exploring the regulatory functions between acetyl-CoA levels and protein acetylation, are highlighted. This review provided new insights into regulating acetyl-CoA synthesis to create more effective microbial cell factories for bio-manufacturing.

Engineering yeast for high-level production of β-farnesene from sole methanol

Methanol, a rich one-carbon feedstock, can be massively produced from CO2 by the liquid sunshine route, which is helpful to realize carbon neutrality. β-Farnesene is widely used in the production of polymers, surfactants, lubricants, and also serves as a suitable substitute for jet fuel. Constructing an efficient cell factory is a feasible approach for β-farnesene production through methanol biotransformation. Here, we extensively engineered the methylotrophic yeast Ogataea polymorpha for the efficient bio-production of β-farnesene using methanol as the sole carbon source. Our study demonstrated that sufficient supply of precursor acetyl-CoA and cofactor NADPH in an excellent yeast chassis had a 1.3-fold higher β-farnesene production than that of wild-type background strain. Further optimization of the mevalonate pathway and enhancement of acetyl-CoA supply led to a 7-fold increase in β-farnesene accumulation, achieving the highest reported sesquiterpenoids production (14.7 g/L with a yield of 46 mg/g methanol) from one-carbon feedstock under fed-batch fermentation in bioreactor. This study demonstrates the great potential of engineering O. polymorpha for high-level terpenoid production from methanol.

Recent advances in lycopene and germacrene a biosynthesis and their role as antineoplastic drugs

Sesquiterpenes and tetraterpenes are classes of plant-derived natural products with antineoplastic effects. While plant extraction of the sesquiterpene, germacrene A, and the tetraterpene, lycopene suffers supply chain deficits and poor yields, chemical synthesis has difficulties in separating stereoisomers. This review highlights cutting-edge developments in producing germacrene A and lycopene from microbial cell factories. We then summarize the antineoplastic properties of β-elemene (a thermal product from germacrene A), sesquiterpene lactones (metabolic products from germacrene A), and lycopene. We also elaborate on strategies to optimize microbial-based germacrene A and lycopene production.

Promoter engineering enables precise metabolic regulation towards efficient β-elemene production in Ogataea polymorpha

Precisely controlling gene expression is beneficial for optimizing biosynthetic pathways for improving the production. However, promoters in nonconventional yeasts such as Ogataea polymorpha are always limited, which results in incompatible gene modulation. Here, we expanded the promoter library in O. polymorpha based on transcriptional data, among which 13 constitutive promoters had the strengths ranging from 0-55% of PGAP, the commonly used strong constitutive promoter, and 2 were growth phase-dependent promoters. Subsequently, 2 hybrid growth phase-dependent promoters were constructed and characterized, which had 2-fold higher activities. Finally, promoter engineering was applied to precisely regulate cellular metabolism for efficient production of β-elemene. The glyceraldehyde-3-phosphate dehydrogenase gene GAP was downregulated to drive more flux into pentose phosphate pathway (PPP) and then to enhance the supply of acetyl-CoA by using phosphoketolase-phosphotransacetylase (PK-PTA) pathway. Coupled with the phase-dependent expression of synthase module (ERG20∼LsLTC2 fusion), the highest titer of 5.24 g/L with a yield of 0.037 g/(g glucose) was achieved in strain YY150U under fed-batch fermentation in shake flasks. This work characterized and engineered a series of promoters, that can be used to fine-tune genes for constructing efficient yeast cell factories.

Characterization of a group of germacrene A synthases involved in the biosynthesis of β-elemene from Atractylodis macrocephala

β-Elemene, an important component of the volatile oil of Atractylodis macrocephala, has been widely utilized as an antitumor drug for over 20 years. However, the germacrene A synthase (GAS) genes responsible for the biosynthesis of β-elemene in A. macrocephala were previously unidentified. In this study, two new AmGASs were identified from the A. macrocephala transcriptome, demonstrating their capability to convert farnesyl pyrophosphate into germacrene A, which subsequently synthesizes β-elemene through Cope rearrangement. Additionally, two highly catalytic AmGAS1 mutations, I307A and E392A, resulted in a 2.23-fold and 1.57-fold increase in β-elemene synthesis, respectively. Furthermore, precursor supply and fed-batch strategies were employed to enhance the precursor supply, resulting in β-elemene yields of 7.3 mg/L and 33.3 mg/L, respectively. These findings identify a promising candidate GAS for β-elemene biosynthesis and lay the foundation for further functional studies on terpene synthases in A. macrocephala.

Biosynthetic pathway redesign in non-conventional yeast for enhanced production of cembratriene-ol

Cembratriene-ol (CBT-ol), a plant-derived macrocyclic diterpene with notable insecticidal activity, has attracted considerable attention with respect to the development of sustainable and green biopesticides. Currently, CBT-ol production is limited by an inefficient and costly plant extraction strategy. Herein, CBT-ol production was enhanced by redesigning the CBT-ol biosynthetic pathway in Candida tropicalis, with subsequent truncation of CBT-ol synthase further increasing CBT-ol production. Moreover, bottlenecks in the CBT-ol biosynthetic pathway were eliminated by adjusting the gene dosage of the rate-limiting enzymes. Ultimately, the resulting strain C. tropicalis CPPt-03D produced 129.17 mg/L CBT-ol in shaking flasks (a 144-fold increase relative to that of the initial strain C01-CD) with CBT-ol production reaching 1,425.76 mg/L in a 5-L bioreactor, representing the highest CBT-ol titer reported to date. These findings provide a green process and promising platform for the industrial production of CBT-ol and lays the foundation for organic farming.

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.

Integration of Yeast Episomal/Integrative Plasmid Causes Genotypic and Phenotypic Diversity and Improved Sesquiterpene Production in Metabolically Engineered Saccharomyces cerevisiae

The variability in phenotypic outcomes among biological replicates in engineered microbial factories presents a captivating mystery. Establishing the association between phenotypic variability and genetic drivers is important to solve this intricate puzzle. We applied a previously developed auxin-inducible depletion of hexokinase 2 as a metabolic engineering strategy for improved nerolidol production in Saccharomyces cerevisiae, and biological replicates exhibit a dichotomy in nerolidol production of either 3.5 or 2.5 g L-1 nerolidol. Harnessing Oxford Nanopore's long-read genomic sequencing, we reveal a potential genetic cause─the chromosome integration of a 2μ sequence-based yeast episomal plasmid, encoding the expression cassettes for nerolidol synthetic enzymes. This finding was reinforced through chromosome integration revalidation, engineering nerolidol and valencene production strains, and generating a diverse pool of yeast clones, each uniquely fingerprinted by gene copy numbers, plasmid integrations, other genomic rearrangements, protein expression levels, growth rate, and target product productivities. Τhe best clone in two strains produced 3.5 g L-1 nerolidol and ∼0.96 g L-1 valencene. Comparable genotypic and phenotypic variations were also generated through the integration of a yeast integrative plasmid lacking 2μ sequences. Our work shows that multiple factors, including plasmid integration status, subchromosomal location, gene copy number, sesquiterpene synthase expression level, and genome rearrangement, together play a complicated determinant role on the productivities of sesquiterpene product. Integration of yeast episomal/integrative plasmids may be used as a versatile method for increasing the diversity and optimizing the efficiency of yeast cell factories, thereby uncovering metabolic control mechanisms.

Methanol bioconversion into C3, C4, and C5 platform chemicals by the yeast Ogataea polymorpha

BACKGROUND

One carbon (C1) molecules such as methanol have the potential to become sustainable feedstocks for biotechnological processes, as they can be derived from CO2 and green hydrogen, without the need for arable land. Therefore, we investigated the suitability of the methylotrophic yeast Ogataea polymorpha as a potential production organism for platform chemicals derived from methanol. We selected acetone, malate, and isoprene as industrially relevant products to demonstrate the production of compounds with 3, 4, or 5 carbon atoms, respectively.

RESULTS

We successfully engineered O. polymorpha for the production of all three molecules and demonstrated their production using methanol as carbon source. We showed that the metabolism of O. polymorpha is well suited to produce malate as a product and demonstrated that the introduction of an efficient malate transporter is essential for malate production from methanol. Through optimization of the cultivation conditions in shake flasks, which included pH regulation and constant substrate feeding, we were able to achieve a maximum titer of 13 g/L malate with a production rate of 3.3 g/L/d using methanol as carbon source. We further demonstrated the production of acetone and isoprene as additional heterologous products in O. polymorpha, with maximum titers of 13.6 mg/L and 4.4 mg/L, respectively.

CONCLUSION

These findings highlight how O. polymorpha has the potential to be applied as a versatile cell factory and contribute to the limited knowledge on how methylotrophic yeasts can be used for the production of low molecular weight biochemicals from methanol. Thus, this study can serve as a point of reference for future metabolic engineering in O. polymorpha and process optimization efforts to boost the production of platform chemicals from renewable C1 carbon sources.

Engineering status of protein for improving microbial cell factories

With the development of metabolic engineering and synthetic biology, microbial cell factories (MCFs) have provided an efficient and sustainable method to synthesize a series of chemicals from renewable feedstocks. However, the efficiency of MCFs is usually limited by the inappropriate status of protein. Thus, engineering status of protein is essential to achieve efficient bioproduction with high titer, yield and productivity. In this review, we summarize the engineering strategies for metabolic protein status, including protein engineering for boosting microbial catalytic efficiency, protein modification for regulating microbial metabolic capacity, and protein assembly for enhancing microbial synthetic capacity. Finally, we highlight future challenges and prospects of improving microbial cell factories by engineering status of protein.

Combination of microbial and chemical synthesis for the sustainable production of β-elemene, a promising plant-extracted anticancer compound

Beta-elemene, a class of sesquiterpene derived from the Chinese medicinal herb Curcuma wenyujin, is widely used in clinical medicine due to its broad-spectrum antitumor activity. However, the unsustainable plant extraction prompted the search for environmentally friendly strategies for β-elemene production. In this study, we designed a Yarrowia lipolytica cell factory that can continuously produce germacrene A, which is further converted into β-elemene with 100% yield through a Cope rearrangement reaction by shifting the temperature to 250°C. First, the productivity of four plant-derived germacrene A synthases was evaluated. After that, the metabolic flux of the precursor to germacrene A was maximized by optimizing the endogenous mevalonate pathway, inhibiting the competing squalene pathway, and expressing germacrene A synthase gene in multiple copies. Finally, the most promising strain achieved the highest β-elemene titer reported to date with 5.08 g/L. This sustainable and green method has the potential for industrial β-elemene production.

Engineering Escherichia coli BL21 (DE3) for high-yield production of germacrene A, a precursor of β-elemene via combinatorial metabolic engineering strategies

β-elemene is one of the most commonly used antineoplastic drugs in cancer treatment. As a plant-derived natural chemical, biologically engineering microorganisms to produce germacrene A to be converted to β-elemene harbors great expectations since chemical synthesis and plant isolation methods come with their production deficiencies. In this study, we report the design of an Escherichia coli cell factory for the de novo production of germacrene A to be converted to β-elemene from a simple carbon source. A series of systematic approaches of engineering the isoprenoid and central carbon pathways, translational and protein engineering of the sesquiterpene synthase, and exporter engineering yielded high-efficient β-elemene production. Specifically, deleting competing pathways in the central carbon pathway ensured the availability of acetyl-coA, pyruvate, and glyceraldehyde-3-phosphate for the isoprenoid pathways. Adopting lycopene color as a high throughput screening method, an optimized NSY305N was obtained via error-prone polymerase chain reaction mutagenesis. Further overexpression of key pathway enzymes, exporter genes, and translational engineering produced 1161.09 mg/L of β-elemene in a shake flask. Finally, we detected the highest reported titer of 3.52 g/L of β-elemene and 2.13 g/L germacrene A produced by an E. coli cell factory in a 4-L fed-batch fermentation. The systematic engineering reported here generally applies to microbial production of a broader range of chemicals. This illustrates that rewiring E. coli central metabolism is viable for producing acetyl-coA-derived and pyruvate-derived molecules cost-effectively.

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.

Development of a Pichia pastoris cell factory for efficient production of germacrene A: a precursor of β-elemene

β-Elemene, an active ingredient found in medicinal plants like turmeric and zedoary, is a sesquiterpene compound with antitumor activity against various cancers. However, its current mode of production through plant extraction suffers from low efficiency and limited natural resources. Recently, there has been an increased interest in establishing microbial cell factories to produce germacrene A, which can be converted to β-elemene by a one-step reaction in vitro. In this study, we constructed an engineered Pichia pastoris cell factory for producing germacrene A. We rerouted the fluxes towards germacrene A biosynthesis through the optimization of the linker sequences between germacrene A synthase (GAS) and farnesyl pyrophosphate synthase (ERG20), overexpression of important pathway genes (i.e., IDI1, tHMG1, and ACS), and multi-copy integration of related expression cassettes. In combination with medium optimization and bioprocess engineering, the final titer of germacrene A in a 1 L fermenter reached 1.9 g/L through fed-batch fermentation. This represents the first report on the production of germacrene A in P. pastoris and demonstrates its advantage in producing terpenoids and other value-added natural products.

Engineering the methylotrophic yeast Ogataea polymorpha for lactate production from methanol

Introduction: Lactate has gained increasing attention as a platform chemical, particularly for the production of the bioplastic poly-lactic acid (PLA). While current microbial lactate production processes primarily rely on the use of sugars as carbon sources, it is possible to envision a future where lactate can be produced from sustainable, non-food substrates. Methanol could be such a potential substrate, as it can be produced by (electro)chemical hydrogenation from CO₂. Methods: In this study, the use of the methylotrophic yeast Ogataea polymorpha as a host organism for lactate production from methanol was explored. To enable lactate production in Ogataea polymorpha, four different lactate dehydrogenases were expressed under the control of the methanol-inducible MOX promoter. The L-lactate dehydrogenase of Lactobacillus helveticus performed well in the yeast, and the lactate production of this engineered strain could additionally be improved by conducting methanol fed-batch experiments in shake flasks. Further, the impact of different nitrogen sources and the resulting pH levels on production was examined more closely. In order to increase methanol assimilation of the lactate-producing strain, an adaptive laboratory evolution experiment was performed. Results and Discussion: The growth rate of the lactate-producing strain on methanol was increased by 55%, while at the same time lactate production was preserved. The highest lactate titer of 3.8 g/L in this study was obtained by cultivating this evolved strain in a methanol fed-batch experiment in shake flasks with urea as nitrogen source. This study provides a proof of principle that Ogataea polymorpha is a suitable host organism for the production of lactate using methanol as carbon source. In addition, it offers guidance for the engineering of methylotrophic organisms that produce platform chemicals from CO₂-derived substrates. With reduced land use, this technology will promote the development of a sustainable industrial biotechnology in the future.