Gene expression pattern analysis of a recombinant Escherichia coli strain possessing high growth and lycopene production capability when using fructose as carbon source

Biochemical and Immunological implications of Lutein and Zeaxanthin

Throughout history, nature has been acknowledged for being a primordial source of various bioactive molecules in which human macular carotenoids are gaining significant attention. Among 750 natural carotenoids, lutein, zeaxanthin and their oxidative metabolites are selectively accumulated in the macular region of living beings. Due to their vast applications in food, feed, pharmaceutical and nutraceuticals industries, the global market of lutein and zeaxanthin is continuously expanding but chemical synthesis, extraction and purification of these compounds from their natural repertoire e.g., plants, is somewhat costly and technically challenging. In this regard microbial as well as microalgal carotenoids are considered as an attractive alternative to aforementioned challenges. Through the techniques of genetic engineering and gene-editing tools like CRISPR/Cas9, the overproduction of lutein and zeaxanthin in microorganisms can be achieved but the commercial scale applications of such procedures needs to be done. Moreover, these carotenoids are highly unstable and susceptible to thermal and oxidative degradation. Therefore, esterification of these xanthophylls and microencapsulation with appropriate wall materials can increase their shelf-life and enhance their application in food industry. With their potent antioxidant activities, these carotenoids are emerging as molecules of vital importance in chronic degenerative, malignancies and antiviral diseases. Therefore, more research needs to be done to further expand the applications of lutein and zeaxanthin.

Transcriptome Analysis Reveals a Promotion of Carotenoid Production by Copper Ions in Recombinant Saccharomyces cerevisiae

We previously constructed a Saccharomyces cerevisiae carotenoid producer BL03-D-4 which produced much more carotenoid in YPM (modified YPD) media than YPD media. In this study, the impacts of nutritional components on carotenoid accumulation of BL03-D-4 were investigated. When using YPM media, the carotenoid yield was increased 10-fold compared to using the YPD media. To elucidate the hidden mechanism, a transcriptome analysis was performed and showed that 464 genes changed significantly in YPM media. Furthermore, inspired by the differential gene expression analysis which indicated that ADY2, HES1, and CUP1 showed the most remarkable changes, we found that the improvement of carotenoid accumulation in YPM media was mainly due to the copper ions, since supplementation of 0.08 mM CuSO₄ in YPD media could increase carotenoid yield 9.2-fold. Reverse engineering of target genes was performed and carotenoid yield could be increased 6.4-fold in YPD media through overexpression of ACE1. The present study revealed for the first time the prominent promotion of carotenoid yield by copper ions in engineered S. cerevisiae and provided a new target ACE1 for genetic engineering of S. cerevisiae for the bioproduction of carotenoids.

Metabolic Engineering of Different Microbial Hosts for Lycopene Production

As a result of the extensive use of lycopene in a variety of fields, especially the dietary supplement and health food industries, the production of lycopene has attracted considerable interest. Lycopene can be obtained through extraction from vegetables and chemical synthesis. Alternatively, the microbial production of lycopene has been extensively researched in recent years. Various types of microbial hosts have been evaluated for their potential to accumulate a high level of lycopene. Metabolic engineering of the hosts and optimization of culture conditions are performed to enhance lycopene production. After years of research, great progress has been made in lycopene production. In this review, strategies used to improve lycopene production in different microbial hosts and the advantages and disadvantages of each microbial host are summarized. In addition, future perspectives of lycopene production in different microbial hosts are discussed.

Modular engineering for microbial production of carotenoids

There is an increasing demand for carotenoids due to their applications in the food, flavor, pharmaceutical and feed industries, however, the extraction and synthesis of these compounds can be expensive and technically challenging. Microbial production of carotenoids provides an attractive alternative to the negative environmental impacts and cost of chemical synthesis or direct extraction from plants. Metabolic engineering and synthetic biology approaches have been widely utilized to reconstruct and optimize pathways for carotenoid overproduction in microorganisms. This review summarizes the current advances in microbial engineering for carotenoid production and divides the carotenoid biosynthesis building blocks into four distinct metabolic modules: 1) central carbon metabolism, 2) cofactor metabolism, 3) isoprene supplement metabolism and 4) carotenoid biosynthesis. These four modules focus on redirecting carbon flux and optimizing cofactor supplements for isoprene precursors needed for carotenoid synthesis. Future perspectives are also discussed to provide insights into microbial engineering principles for overproduction of carotenoids.

Design and tailoring of an artificial DNA scaffolding system for efficient lycopene synthesis using zinc-finger-guided assembly

A highly efficient lycopene production system was constructed by assembling enzymes fused to zinc-finger motifs on DNA scaffolds in vitro and in vivo. Three key enzymes of the lycopene synthesis pathway, geranylgeranyl diphosphate synthase, phytoene synthase, and phytoene desaturase, were fused with zinc-finger proteins, expressed and purified. Recombinant plasmids of the pS series containing DNA scaffolds that the zinc-finger proteins can specifically bind to were constructed. In the in vitro system, the production efficiency of lycopene was improved greatly after the addition of the scaffold plasmid pS231. Subsequently, the plasmid pET-AEBI was constructed and introduced into recombinant Escherichia coli BL21 (DE3) for expression, together with plasmids of the pS series. The lycopene production rate and content of the recombinant strain pp231 were higher than that of all strains carrying the DNA scaffold and the control. With the addition of cofactors and substrates in the lycopene biosynthesis pathway, the lycopene yield of pp231 reached 632.49 mg/L at 40 h, representing a 4.7-fold increase compared to the original recombinant strain pA1A3. This DNA scaffold system can be used as a platform for the construction and production of many biochemicals synthesized via multi-enzyme cascade reactions.

Primary and Secondary Metabolic Effects of a Key Gene Deletion (ΔYPL062W) in Metabolically Engineered Terpenoid-Producing Saccharomyces cerevisiae

Saccharomyces cerevisiae is an established cell factory for production of terpenoid pharmaceuticals and chemicals. Numerous studies have demonstrated that deletion or overexpression of off-pathway genes in yeast can improve terpenoid production. The deletion of YPL062W in S. cerevisiae, in particular, has benefitted carotenoid production by channeling carbon toward carotenoid precursors acetyl coenzyme A (acetyl-CoA) and mevalonate. The genetic function of YPL062W and the molecular mechanisms for these benefits are unknown. In this study, we systematically examined this gene deletion to uncover the gene function and its molecular mechanism. RNA sequencing (RNA-seq) analysis uncovered that YPL062W deletion upregulated the pyruvate dehydrogenase bypass, the mevalonate pathway, heterologous expression of galactose (GAL) promoter-regulated genes, energy metabolism, and membrane composition synthesis. Bioinformatics analysis and serial promoter deletion assay revealed that YPL062W functions as a core promoter for ALD6 and that the expression level of ALD6 is negatively correlated to terpenoid productivity. We demonstrate that ΔYPL062W increases the production of all major terpenoid classes (C₁₀, C₁₅, C₂₀, C₃₀, and C₄₀). Our study not only elucidated the biological function of YPL062W but also provided a detailed methodology for understanding the mechanistic aspects of strain improvement.IMPORTANCE Although computational and reverse metabolic engineering approaches often lead to improved gene deletion mutants for cell factory engineering, the systems level effects of such gene deletions on the production phenotypes have not been extensively studied. Understanding the genetic and molecular function of such gene alterations on production strains will minimize the risk inherent in the development of large-scale fermentation processes, which is a daunting challenge in the field of industrial biotechnology. Therefore, we established a detailed experimental and systems biology approach to uncover the molecular mechanisms of YPL062W deletion in S. cerevisiae, which is shown to improve the production of all terpenoid classes. This study redefines the genetic function of YPL062W, demonstrates a strong correlation between YPL062W and terpenoid production, and provides a useful modification for the creation of terpenoid production platform strains. Further, this study underscores the benefits of detailed and systematic characterization of the metabolic effects of genetic alterations on engineered biosynthetic factories.

Effects of lipopolysaccharide structure on lycopene production in Escherichia coli

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The heterogenous crtEBI operon was overexpressed in 10 LPS mutant strains of E. coli W3110.

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ΔwaaC/pWSK29-crtEBI and ΔwaaF/pWSK29-crtEBI produced more lycopene than others.

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Overexpressing dxr, dxr, ispA and idi in ΔwaaC/pWSK29-crtEBI and ΔwaaF/pWSK29-crtEBI enhanced lycopene production.

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The maximum yield of 5.39 mg/g was produced in ΔwaaC/pWSK29-crtEBI-SRA.

Lipopolysaccharides, the major molecules in the outer membrane of Escherichia coli, affect the behavior of bacteria including outer membrane permeability, but its influence on lycopene production in E. coli has never been reported. In this study, the effects of lipopolysaccharides with different structures on lycopene biosynthesis were investigated. Firstly, the heterogenous crtEBI operon were overexpressed in 10 LPS mutant strains of E. coli W3110 (ΔwaaC, ΔwaaF, ΔwaaY, ΔwaaG, ΔwaaR, ΔwaaO, ΔwaaU, ΔwaaP, ΔwaaY and ΔwaaB), and their ability to produce lycopene were compared. ΔwaaC/pWSK29-crtEBI, ΔwaaF/pWSK29-crtEBI and ΔwaaY/pWSK29-crtEBI produced 4.19, 4.20, and 3.81 mg/g lycopene, respectively, while the control W3110/pWSK29-crtEBI produced 3.71 mg/g lycopene; the other strains produced less lycopene than the control. In order to enhance lycopene production, genes dxr, dxr, ispA, and idi were overexpressed in ΔwaaC/pWSK29-crtEBI, ΔwaaF/pWSK29-crtEBI individually or in combination, and the lycopene production in each strain was analyzed. The maximum yield of 5.39 mg/g was achieved in ΔwaaC/pWSK29-crtEBI-SRA, which is 142% higher than that in W3110/pWSK29-crtEBI. The results indicate that the length of lipopolysaccharide affects lycopene biosynthesis in E. coli, and the shorter lipopolysaccharide and higher outer membrane permeability might be beneficial to lycopene biosynthesis.