Production of β-carotene by recombinant Escherichia coli with engineered whole mevalonate pathway in batch and fed-batch cultures

A combination fermentation strategy for simultaneously increasing cellular NADP(H) level, biomass, and enzymatic activity of glufosinate dehydrogenase in Escherichia coli

Oxidoreductase is one of the most important biocatalysts for the synthesis of various chiral compounds. However, their whole-cell activity is frequently affected by an insufficient supply of expensive nicotinamide cofactors. This study aimed to overcome such shortcomings by developing a combination fermentation strategy for simultaneously increasing intracellular NADP(H) level, biomass, and glufosinate dehydrogenase activity in E. coli. The results showed that the feeding mode of NAD(H) synthesis precursor and lactose inducer had essential effects on the accumulation level of intracellular NADPH. Adding 40 mg L^-1 of L-aspartic acid to the medium increased the intracellular NADP(H) concentration by 36.3%. Under the pH-stat feeding mode and adding 0.4 g L^-1 h^-1 lactose, the NADP(H) concentration, biomass, and GluDH activity in the 5-L fermenter reached 445.7 μmol L^-1, 21.7 gDCW L^-1, and 8569.3 U L^-1, respectively. As far as we know, this is the highest reported activity of GluDH in the fermentation broth. Finally, the 5000-L fermenter was successfully scaled up to use this fermentation approach. The combination fermentation strategy might serve as a useful approach for the high-activity fermentation of other NADPH-dependent oxidoreductases.

Advances in the synthesis of three typical tetraterpenoids including β-carotene, lycopene and astaxanthin

Carotenoids are natural pigments that widely exist in nature. Due to their excellent antioxidant, anticancer and anti-inflammatory properties, carotenoids are commonly used in food, medicine, cosmetic and other fields. At present, natural carotenoids are mainly extracted from plants, algae and microorganisms. With the rapid development of metabolic engineering and molecular biology as well as the continuous in-depth study of carotenoids synthesis pathways, industrial microorganisms have showed promising applications in the synthesis of carotenoids. In this review, we introduced the properties of several carotenoids and their biosynthetic metabolism process. Then, the microorganisms synthesizing carotenoids through the natural and non-natural pathways and the extraction methods of carotenoids were summarized and compared. Meanwhile, the influence of substrates on the carotenoids production was also listed. The methods and strategies for achieving high carotenoid production are categorized to help with future research.

Pathway engineering and medium optimization for α-farnesene biosynthesis in oleaginous yeast Yarrowia lipolytica

Farnesene is a typical sesquiterpene with applications as fragrance, flavor and precursor for the synthesis of vitamin E/K1. In this study, a series of strategies were employed to facilitate α-farnesene accumulation in Yarrowia lipolytica. Among them, the promoter optimization of OptFSLERG20, Sc-tHMG1 and IDI resulted in more than 62 % increase in α-farnesene production. Together with the overexpression of Yl-HMGR and ERG19, α-farnesene content was significantly improved by more than 3.5 times. The best metabolic engineered strain obtained was therefore used for a uniform design in shake flasks to determine the optimal medium compositions. Furthermore, a maximum α-farnesene production of approximately 2.57 g/L (34 mg/g DCW) was obtained in fed-batch fermentation where glycerol was supplemented as the feeding carbon source when initial glucose was depleted. This study has laid a good foundation for the development of Y. lipolytica as a promising chassis microbial cell for heterologous biosynthesis of α-farnesene and other sesquiterpenes.

Exploiting the Feedstock Flexibility of the Emergent Synthetic Biology Chassis Vibrio natriegens for Engineered Natural Product Production

A recent goal of synthetic biology has been to identify new chassis that provide benefits lacking in model organisms. Vibrio natriegens is a marine Gram-negative bacterium which is an emergent synthetic biology chassis with inherent benefits: An extremely fast growth rate, genetic tractability, and the ability to grow on a variety of carbon sources ("feedstock flexibility"). Given these inherent benefits, we sought to determine its potential to heterologously produce natural products, and chose beta-carotene and violacein as test cases. For beta-carotene production, we expressed the beta-carotene biosynthetic pathway from the sister marine bacterium Vibrio campbellii, as well as the mevalonate biosynthetic pathway from the Gram-positive bacterium Lactobacillus acidophilus to improve precursor abundance. Violacein was produced by expressing a biosynthetic gene cluster derived from Chromobacterium violaceum. Not only was V. natriegens able to heterologously produce these compounds in rich media, illustrating its promise as a new chassis for small molecule drug production, but it also did so in minimal media using a variety of feedstocks. The ability for V. natriegens to produce natural products with multiple industrially-relevant feedstocks argues for continued investigations into the production of more complex natural products in this chassis.

Valorification of crude glycerol for pure fractions of docosahexaenoic acid and β-carotene production by using Schizochytrium limacinum and Blakeslea trispora

The goal of this research is the investigation of a way to maximize the production of docosahexaenoic acid (DHA) and β-carotene by optimizing the culture conditions of their sources, microalgae Schizochytrium limacinum and fungus Blakeslea trispora respectively, in a fermentation medium. The influencing factors in the fermentation process for producing DHA and β-carotene have proven to be: the concentration of carbon source (different glycerol crude and pure concentrations) for both of them, and in particular temperature for DHA and pH for β-carotene. Testing the effect of these parameters was determined: biomass, DHA and β-carotene concentration. The highest production by S. limacinum was obtained at 25 °C, while using a quantity of 90 g/L of glycerol (crude or pure) as a carbon source. Temperature was the main factor that influenced the biosynthesis of DHA. The quantification of DHA was made by GC–MS chromatography, followed by a purification process, with the end result of DHA in pure phase. The maximum quantities for β-carotene production were obtained with pH 7 and 60 g/L of crude glycerol. The results highlight the possibility of using crude glycerol as a low-cost substrates for growth of microalgae S. limacinum and of fungus B. trispora in order to obtain the crucial molecules: docosahexaenoic acid and β-carotene.

Iterative integration of multiple-copy pathway genes in Yarrowia lipolytica for heterologous β-carotene production

β-Carotene is a terpenoid molecule with high hydrophobicity that is often used as an additive in foods and feed. Previous work has demonstrated the heterologous biosynthesis of β-carotene from an intrinsic high flux of acetyl-CoA in 12 steps through 11 genes in Yarrowia lipolytica. Here, an efficient biosynthetic pathway capable of producing 100-fold more β-carotene than the baseline construct was generated using strong promoters and multiple gene copies for each of the 12 steps. Using fed-batch fermentation with an optimized medium, the engineered pathway could produce 4g/L β-carotene, which was stored in lipid droplets within engineered Y. lipolytica cells. Expansion of these cells for squalene production also demonstrated that Y. lipolytica could be an industrially relevant platform for hydrophobic terpenoid production.

The potential of the mevalonate pathway for enhanced isoprenoid production

The cytosol-localised mevalonic acid (MVA) pathway delivers the basic isoprene unit isopentenyl diphosphate (IPP). In higher plants, this central metabolic intermediate is also synthesised by the plastid-localised methylerythritol phosphate (MEP) pathway. Both MVA and MEP pathways conspire through exchange of intermediates and regulatory interactions. Products downstream of IPP such as phytosterols, carotenoids, vitamin E, artemisinin, tanshinone and paclitaxel demonstrate antioxidant, cholesterol-reducing, anti-ageing, anticancer, antimalarial, anti-inflammatory and antibacterial activities. Other isoprenoid precursors including isoprene, isoprenol, geraniol, farnesene and farnesol are economically valuable. An update on the MVA pathway and its interaction with the MEP pathway is presented, including the improvement in the production of phytosterols and other isoprenoid derivatives. Such attempts are for instance based on the bioengineering of microbes such as Escherichia coli and Saccharomyces cerevisiae, as well as plants. The function of relevant genes in the MVA pathway that can be utilised in metabolic engineering is reviewed and future perspectives are presented.

The Putative mevalonate diphosphate decarboxylase from Picrophilus torridus is in reality a mevalonate-3-kinase with high potential for bioproduction of isobutene

Mevalonate diphosphate decarboxylase (MVD) is an ATP-dependent enzyme that catalyzes the phosphorylation/decarboxylation of (R)-mevalonate-5-diphosphate to isopentenyl pyrophosphate in the mevalonate (MVA) pathway. MVD is a key enzyme in engineered metabolic pathways for bioproduction of isobutene, since it catalyzes the conversion of 3-hydroxyisovalerate (3-HIV) to isobutene, an important platform chemical. The putative homologue from Picrophilus torridus has been identified as a highly efficient variant in a number of patents, but its detailed characterization has not been reported. In this study, we have successfully purified and characterized the putative MVD from P. torridus. We discovered that it is not a decarboxylase per se but an ATP-dependent enzyme, mevalonate-3-kinase (M3K), which catalyzes the phosphorylation of MVA to mevalonate-3-phosphate. The enzyme's potential in isobutene formation is due to the conversion of 3-HIV to an unstable 3-phosphate intermediate that undergoes consequent spontaneous decarboxylation to form isobutene. Isobutene production rates were as high as 507 pmol min⁻¹ g cells⁻¹ using Escherichia coli cells expressing the enzyme and 2,880 pmol min⁻¹ mg protein⁻¹ with the purified histidine-tagged enzyme, significantly higher than reported previously. M3K is a key enzyme of the novel MVA pathway discovered very recently in Thermoplasma acidophilum. We suggest that P. torridus metabolizes MVA by the same pathway.

Feeding strategies for the improved biosynthesis of canthaxanthin from enzymatic hydrolyzed molasses in the fed-batch fermentation of Dietzia natronolimnaea HS-1

The effect of two enzymatic hydrolyzed molasses (EHM)-feeding strategies including constant-(CFR) and exponential-(EFR) feeding rate on canthaxanthin (CTX) biosynthesis by Dietzia natronolimnaea HS-1 fed-batch fermentation was studied. The results showed that the CFR of 7 ml/h with an EHM content of 45 g/l led to the highest values of specific growth rate (0.127 h(-1)), biomass dry weight (17.66 g/l), total carotenoid (16.31 mg/l) and CTX (14.67 mg/l). A significant decrease in the kinetic growth and production parameters by the increasing EHM concentration from 30 to 60 g/l during EFR fed-batch bioprocess was observed (p<0.01). This study concluded that EHM alone can displace glucose-based medium towards improved CTX biosynthesis from D. natronolimnaea HS-1 using a CFR strategy during fed-batch culture.

High-yield production of the VP1 structural protein epitope from serotype O foot-and-mouth disease virus in Escherichia coli

For effective control of foot-and-mouth disease (FMD), the development of rapid diagnostic systems and vaccines are required against its etiological agent, FMD virus (FMDV). To accomplish this, efficient large-scale expression of the FMDV VP1 protein, with high solubility, needs to be optimized. We attempted to produce high levels of a serotype O FMDV VP1 epitope in Escherichia coli. We identified the subtype-independent serotype O FMDV VP1 epitope sequence and used it to construct a glutathione S-transferase (GST) fusion protein. For efficient production of the FMDV VP1 epitope fused to GST (VP1e-GST), four E. coli strains and three temperatures were examined. The conditions yielding the greatest level of VP1e-GST with highest solubility were achieved with E. coli BL21(DE3) at 25 °C. For high-level production, fed-batch cultures were conducted in 5-l bioreactors. When cells were induced at a high density and complex feeding solutions were supplied, approximately 11 g of VP1e-GST was obtained from a 2.9-l culture. Following purification, the VP1 epitope was used to immunize rabbits, and we confirmed that it induced an immune response.