Improved Membrane Permeability via Hypervesiculation for In Situ Recovery of Lycopene in Escherichia coli

In situ production and precise release of bioactive GM-CSF and siRNA by engineered bacteria for macrophage reprogramming in cancer immunotherapy

In the immunosuppressive tumor microenvironment (TME), tumor-associated macrophages (TAMs) predominantly exhibit an immunosuppressive M2 phenotype, which facilitates tumor proliferation and metastasis. Although current strategies aimed at reprogramming TAMs hold promise, their sustainability and effectiveness are limited due to repeated injections. Herein, a bacterial therapy platform containing two engineered strains was developed. One strain was engineered to produce and secrete granulocyte-macrophage colony-stimulating factor (GM-CSF) to promote M2-like TAMs repolarization to M1-like TAMs, while the other strain was designed to secrete small interfering RNA (siRNA) targeting signal regulatory protein α (SIRPα). The two strains can continuously and efficiently produce bioactive therapeutic agents in situ, exerting a sustained and synergistic therapeutic effect in TAMs to inhibit tumor growth. To enhance treatment efficacy, optogenetic strategy was implemented to effectively control the production of GM-CSF, and outer membrane vesicles (OMVs) produced by engineered bacteria were utilized to protect the siRNA from degradation in the external environment. The experimental results indicated that the bacterial therapy platform could continuously produce and release bioactive GM-CSF and SIRPα siRNA, exhibiting significant therapeutic activity. In vivo experiments further demonstrated that this platform showed more sustained and stable therapeutic effects compared to conventional drug therapies. Additionally, the combination of these two engineered strains yielded the highest ratio of M1/M2 TAMs (0.80) and the lowest ratio of F4/80+SIRPα+TAMs (3.46 %) than single strain therapy. Our study expanded the potential of engineered bacteria as pharmaceutical factories for in vivo therapeutic applications.

Metabolic Engineering of Escherichia coli for Enhanced Production of Cembratrien-ols via Precursor Supply Optimization and Membrane Engineering

Cembratrien-ols (CBT-ols) are diterpenoid compounds derived from Nicotiana plants, exhibit significant insecticidal activity, and have attracted considerable attention for the development of sustainable biopesticides. In this study, an efficient CBT-ols biosynthesis strain was constructed by integrating an artificial isopentenol utilization pathway into Escherichia coli. Multiple endogenous pyrophosphatase genes were systematically knocked out to enhance precursor supply, increasing CBT-ol production to 211.6 ± 5.74 mg/L. To further promote CBT-ol accumulation, cell membrane engineering was employed to expand membrane storage capacity, resulting in a yield of 475.6 ± 13.73 mg/L. Through fermentation optimization via continuous feeding, the engineered strain produced a final yield of 2.87 g/L in a 5 L bioreactor, with a substrate conversion rate of 44.3%, which represents the highest reported yield to date. These findings underscore the substantial benefits of the isopentenol utilization pathway in optimizing synthesis processes, thereby establishing a more robust foundation for the production of isoprenoid compounds.

Cell membrane engineering of Bacillus licheniformis for the enhancement of heterologous protein production

Heterologous expression is crucial to produce various recombinants proteins, yet consistently achieving high yields poses a significant challenge. The main objective of our research was to engineer the cell membrane components of Bacillus licheniformis for improving heterologous proteins production. This engineering strategy was achieved by overexpressing genes bkdR, plsY, plsC, and deleting pssA and clsA, which significantly increased the production of nattokinase, α-amylase and keratinase. Furthermore, a combined engineered strain was constructed by integrating all these approaches into a single strain (DW2-RYCAS) which led to an increase in the negative charge and permeability of the cell membrane by 41.11 % and 57.62 %, respectively, and reduced cell membrane integrity by 81.45 % compared to the control strain DW2. Ultimately, the production of nattokinase, α-amylase, and keratinase in DW2-RYCAS were 406.02 ± 8.17 FU/mL, 526.80 ± 14.77 U/mL, and 18.27 ± 0.70 KU/mL, respectively, which increased by 493.59 %, 273.40 %, and 213.91 % compared to the control strain DW2. These results represent the highest production of nattokinase, α-amylase, and keratinase in shake flasks reported to date. Our research illustrated the promising application of cell membrane engineering in B. licheniformis, creating an excellent platform for the biosynthesis of heterologous proteins.

Screening and engineering of lycopene-producing strain Rhodococcus jostii for bio-upcycling of poly(ethylene terephthalate) waste

Poly(ethylene terephthalate) (PET) is a widely used plastic, but its improper disposal has caused serious environmental pollution. The development of bioconversion for PET waste into high-value chemicals has gained significant attention as an innovative solution. In this study, a novel guided screening strategy involving mixed-bacteria fermentation and partitioned purification (MBF) was proposed to first successful isolate Rhodococcus jostii LETBE 8896, a strain capable of naturally producing 4 μg/L of lycopene from PET hydrolysate. Transcriptomic analysis identified the methylerythritol 4-phosphate (MEP) pathway as key to lycopene biosynthesis, with IspG identified as a critical regulatory enzyme. R. jostii with ispG overexpression enhanced lycopene production, with 819 μg/L in the simulated PET hydrolysate and 650 μg/L in the PET hydrolysate. Additionally, the use of butylated hydroxytoluene (BHT) as an antioxidant significantly improved lycopene production at 1 L scale level, achieving a maximum yield of 1865 μg/L with a molar conversion rate of 50.36 % from the PET hydrolysate, the highest reported for PET hydrolysate to date. These findings highlight the dual potential of R. jostii as a chassis strain for high-value chemical production and as a sustainable solution for PET upcycling. This study provides a novel approach to plastic waste management, contributing to the circular economy and global sustainability goals.

Engineering Escherichia coli via introduction of the isopentenol utilization pathway to effectively produce geranyllinalool

BACKGROUND

Geranyllinalool, a natural diterpenoid found in plants, has a floral and woody aroma, making it valuable in flavors and fragrances. Currently, its synthesis primarily depends on chemical methods, which are environmentally harmful and economically unsustainable. Microbial synthesis through metabolic engineering has shown potential for producing geranyllinalool. However, achieving efficient synthesis remains challenging owing to the limited availability of terpenoid precursors in microorganisms. Thus, an artificial isopentenol utilization pathway (IUP) was constructed and introduced in Escherichia coli to enhance precursor availability and further improve terpenoid synthesis.

RESULTS

We first constructed an artificial IUP in E. coli to enhance the supply of precursor geranylgeranyl diphosphate (GGPP) and then screened geranyllinalool synthases from plants to achieve efficient synthesis of geranyllinalool (274.78 ± 2.48 mg/L). To further improve geranyllinalool synthesis, we optimized various cultivation factors, including carbon source, IPTG concentration, and prenol addition and obtained 447.51 ± 6.92 mg/L of geranyllinalool after 72 h of shaken flask fermentation. Moreover, a scaled-up production in a 5-L fermenter was investigated to give 2.06 g/L of geranyllinalool through fed-batch fermentation. To the best of our knowledge, this is the highest reported titer so far.

CONCLUSIONS

Efficient synthesis of geranyllinalool in E. coli can be achieved through a two-step pathway and optimization of culture conditions. The findings of this study provide valuable insights into the production of other terpenoids in E. coli.

Bacterial surface display of PETase mutants and MHETase for an efficient dual-enzyme cascade catalysis

Biological degradation of PET plastic holds great potential for plastic recycling. However, the high costs associated with preparing free enzymes for degrading PET make it unfeasible for industrial applications. Hence, we developed various cell catalysts by surface-displaying PETase mutants and MHETase using autotransporters in E. coli and P. putida. The efficiency of surface display was enhanced through modifying the host, co-expressing molecular chaperones, and evoluting the autotransporter. In strain EC9F, PET degradation rate was boosted to 3.85 mM/d, 51-fold and 23-fold increase compared to free enzyme and initial strain ED1, respectively. The reusability of cell catalyst EC9F was demonstrated with over 38 % and 30 % of its initial activity retained after 22 cycles of BHET degradation and 3 cycles of PET degradation. The highest reported PET degradation rate of 4.95 mM/d was achieved by the dual-enzyme cascade catalytic system EC9F+EM2+R, a mixture of cell catalyst EC9F and EM2 with surfactant rhamnolipid.

Highly flexible cell membranes are the key to efficient production of lipophilic compounds

Lipophilic compounds have a variety of positive effects on human physiological functions and exhibit good effects in the prevention and treatment of clinical diseases. This has led to significant interest in the technical applications of synthetic biology for the production of lipophilic compounds. However, the strict selective permeability of the cell membrane and the hydrophobic nature of lipophilic compounds pose significant challenges to their production. During fermentation, lipophilic compounds tend to accumulate within cell membrane compartments rather than being secreted extracellularly. The toxic effects of excessive lipophilic compound accumulation can threaten cell viability, while the limited space within the cell membrane restricts further increases in production yield. Consequently, to achieve efficient production of lipophilic compounds, research is increasingly focused on constructing robust and multifunctional microbial cell factories. Utilizing membrane engineering techniques to construct highly flexible cell membranes is considered an effective strategy to break through the upper limit of lipophilic compound production. Currently, there are two main approaches to cell membrane modification: constructing artificial storage compartments for lipophilic compounds and engineering the cell membrane structure to facilitate product outflow. This review summarizes recent cell membrane engineering strategies applied in microbial cell factories for the production of liposoluble compounds, discussing the challenges and future prospects. These strategies enhance membrane flexibility and effectively promote the production of liposoluble compounds.

Development of a vitamin B5 hyperproducer in Escherichia coli by multiple metabolic engineering

Vitamin B5 [D-pantothenic acid (D-PA)] is an essential water-soluble vitamin that is widely used in the food and feed industries. Currently, the relatively low fermentation efficiency limits the industrial application of D-PA. Here, a plasmid-free D-PA hyperproducer was constructed using systematic metabolic engineering strategies. First, pyruvate was enriched by deleting the non-phosphotransferase system, inhibiting pyruvate competitive branches, and dynamically controlling the TCA cycle. Next, the (R)-pantoate pathway was enhanced by screening the rate-limiting enzyme PanBC and regulating the other enzymes of this pathway one by one. Then, to enhance NADPH sustainability, NADPH regeneration was achieved through the novel "PEACES" system by (1) expressing the NAD + kinase gene ppnk from Clostridium glutamicum and the NADP + -dependent gapCcae from Clostridium acetobutyricum and (2) knocking-out the endogenous sthA gene, which interacts with ilvC and panE in the D-PA biosynthesis pathway. Combined with transcriptome analysis, it was found that the membrane proteins OmpC and TolR promoted D-PA efflux by increasing membrane fluidity. Strain PA132 produced a D-PA titer of 83.26 g/L by two-stage fed-batch fermentation, which is the highest D-PA titer reported so far. This work established competitive producers for the industrial production of D-PA and provided an effective strategy for the production of related products.

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.

Transcending membrane barriers: advances in membrane engineering to enhance the production capacity of microbial cell factories

Microbial cell factories serve as pivotal platforms for the production of high-value natural products, which tend to accumulate on the cell membrane due to their hydrophobic properties. However, the limited space of the cell membrane presents a bottleneck for the accumulation of these products. To enhance the production of intracellular natural products and alleviate the burden on the cell membrane caused by product accumulation, researchers have implemented various membrane engineering strategies. These strategies involve modifying the membrane components and structures of microbial cell factories to achieve efficient accumulation of target products. This review summarizes recent advances in the application of membrane engineering technologies in microbial cell factories, providing case studies involving Escherichia coli and yeast. Through these strategies, researchers have not only improved the tolerance of cells but also optimized intracellular storage space, significantly enhancing the production efficiency of natural products. This article aims to provide scientific evidence and references for further enhancing the efficiency of similar cell factories.

Advances in the Discovery and Engineering of Gene Targets for Carotenoid Biosynthesis in Recombinant Strains

Carotenoids are naturally occurring pigments that are abundant in the natural world. Due to their excellent antioxidant attributes, carotenoids are widely utilized in various industries, including the food, pharmaceutical, cosmetic industries, and others. Plants, algae, and microorganisms are presently the main sources for acquiring natural carotenoids. However, due to the swift progress in metabolic engineering and synthetic biology, along with the continuous and thorough investigation of carotenoid biosynthetic pathways, recombinant strains have emerged as promising candidates to produce carotenoids. The identification and manipulation of gene targets that influence the accumulation of the desired products is a crucial challenge in the construction and metabolic regulation of recombinant strains. In this review, we provide an overview of the carotenoid biosynthetic pathway, followed by a summary of the methodologies employed in the discovery of gene targets associated with carotenoid production. Furthermore, we focus on discussing the gene targets that have shown potential to enhance carotenoid production. To facilitate future research, we categorize these gene targets based on their capacity to attain elevated levels of carotenoid production.