Production of itaconic acid in Escherichia coli expressing recombinant α-amylase using starch as substrate

Engineering Bacillus licheniformis as industrial chassis for efficient bioproduction from starch

Starch is an attractive feedstock in biorefinery processes, while the low natural conversion rate of most microorganisms limits its applications. Herein, starch metabolic pathway was systematically investigated using Bacillus licheniformis DW2 as the host organism. Initially, the effects of overexpressing amylolytic enzymes on starch hydrolysis were evaluated. Subsequently, the transmembrane transport system and intracellular degradation module were modified to accelerate the uptake of hydrolysates and their further conversion to glucose-6-phosphate. The DW2-derived strains exhibited robust growth in starch medium, and productivity of bacitracin and subtilisin were improved by 38.5% and 32.6%, with an 32.3% and 22.9% increase of starch conversion rate, respectively. Lastly, the employment of engineering strategies enabled another B. licheniformis WX-02 to produce poly-γ-glutamic acid from starch with a 2.1-fold increase of starch conversion rate. This study not only provided excellent B. licheniformis chassis for sustainable bioproduction from starch, but shed light on researches of substrate utilization.

Production of glycerate from glucose using engineered Escherichiacoli

In this study, glycerate was produced from glucose using engineered Escherichia coli BW25113. Plasmid pSR3 carrying gpd1 and gpp2 encoding two isoforms of glycerol-3-phosphate dehydrogenase from Saccharomyces cerevisiae and plasmid pLB2 carrying aldO encoding alditol oxidase from Streptomyces violaceoruber were introduced into E. coli to enable the production of glycerate from glucose via glycerol. Disruptions of garK and glxK genes in the E. coli genome were performed to minimize the consumption of glycerate produced. As a result, E. coli carrying these plasmids could produce nearly three times higher concentration of glycerate (0.50 ± 0.01 g/L) from 10 g/L glucose compared to E. coli EG_2 (0.14 ± 0.02 g/L). In M9 medium, disruption of garK and glxK resulted in an impaired growth rate with low production of glycerate, while supplementation of 0.5 g/L casamino acids and 0.5 g/L manganese sulfate to the medium replenished the growth rate and elevated the glycerate titer. Further disruption of glpF, encoding a glycerol transporter, increased the glycerate production to 0.80 ± 0.00 g/L. MR2 medium improved the glycerate production titers and specific productivities of E. coli EG_4, EG_5, and EG_6. Upscale production of glycerate was carried out in a jar fermentor with MR2 medium using E. coli EG_6, resulting in an improvement in glycerate production up to 2.37 ± 0.46 g/L with specific productivity at 0.34 ± 0.11 g-glycerate/g-cells. These results indicate that E. coli is an appropriate host for glycerate production from glucose.

Recent Advances on the Production of Itaconic Acid via the Fermentation and Metabolic Engineering

Itaconic acid (ITA) is one of the top 12 platform chemicals. The global ITA market is expanding due to the rising demand for bio-based unsaturated polyester resin and its non-toxic qualities. Although bioconversion using microbes is the main approach in the current industrial production of ITA, ecological production of bio-based ITA faces several issues due to: low production efficiency, the difficulty to employ inexpensive raw materials, and high manufacturing costs. As metabolic engineering advances, the engineering of microorganisms offers a novel strategy for the promotion of ITA bio-production. In this review, the most recent developments in the production of ITA through fermentation and metabolic engineering are compiled from a variety of perspectives, including the identification of the ITA synthesis pathway, the metabolic engineering of natural ITA producers, the design and construction of the ITA synthesis pathway in model chassis, and the creation, as well as application, of new metabolic engineering strategies in ITA production. The challenges encountered in the bio-production of ITA in microbial cell factories are discussed, and some suggestions for future study are also proposed, which it is hoped offers insightful views to promote the cost-efficient and sustainable industrial production of ITA.

Recent advances and perspectives on production of value-added organic acids through metabolic engineering

Organic acids are important consumable materials with a wide range of applications in the food, biopolymer and chemical industries. The global consumer organic acids market is estimated to increase to $36.86 billion by 2026. Conventionally, organic acids are produced from the chemical catalysis process with petrochemicals as raw materials, which posts severe environmental concerns and conflicts with our sustainable development goals. Most of the commonly used organic acids can be produced from various organisms. As a state-of-the-art technology, large-scale fermentative production of important organic acids with genetically-modified microbes has become an alternative to the chemical route to meet the market demand. Despite the fact that bio-based organic acid production from renewable cheap feedstock provides a viable solution, low productivity has impeded their industrial-scale application. With our deeper understanding of strain genetics, physiology and the availability of strain engineering tools, new technologies including synthetic biology, various metabolic engineering strategies, omics-based system biology tools, and high throughput screening methods are gradually established to bridge our knowledge gap. And they were further applied to modify the cellular reaction networks of potential microbial hosts and improve the strain performance, which facilitated the commercialization of consumable organic acids. Here we present the recent advances of metabolic engineering strategies to improve the production of important organic acids including fumaric acid, citric acid, itaconic acid, adipic acid, muconic acid, and we also discuss the current challenges and future perspectives on how we can develop a cost-efficient, green and sustainable process to produce these important chemicals from low-cost feedstocks.

A polymerizable difunctional photoinitiator featuring a bio-based group and its photoinitiating properties

A polymerizable difunctional photoinitiator 2-methylene-succinic acid bis-{2-[4-(2-hydroxy-2-methylpropionyl)phenoxy]ethyl} ester (IAHHMP) based on the commercial photoinitiator 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methylpropanone (HHMP) and a biorenewable itaconic acid is synthesized by esterification. The structure is confirmed by ultraviolet spectroscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy (1H NMR, 13C NMR) and thermogravimetric analysis. The photopolymerization behaviour of the photoinitiator is investigated using photo-differential scanning calorimetry and compared with that of two commercial photoinitiators, HHMP (or photoinitiator 2959) and 1-hydroxycyclohexyl phenyl ketone (or photoinitiator 184). The results show that IAHHMP has a strong UV absorption capacity at 245~300 nm and can initiate polymerization of monomers containing a double bond. The relative migration of IAHHMP is less than that of the systems containing an HHMP or 1-hydroxycyclohexyl phenyl ketone photoinitiator. Therefore, IAHHMP is expected to have potential applications in more environmentally friendly materials, such as in food and medical packaging.

Metabolic Engineering and Regulation of Diol Biosynthesis from Renewable Biomass in Escherichia coli

As bulk chemicals, diols have wide applications in many fields, such as clothing, biofuels, food, surfactant and cosmetics. The traditional chemical synthesis of diols consumes numerous non-renewable energy resources and leads to environmental pollution. Green biosynthesis has emerged as an alternative method to produce diols. Escherichia coli as an ideal microbial factory has been engineered to biosynthesize diols from carbon sources. Here, we comprehensively summarized the biosynthetic pathways of diols from renewable biomass in E. coli and discussed the metabolic-engineering strategies that could enhance the production of diols, including the optimization of biosynthetic pathways, improvement of cofactor supplementation, and reprogramming of the metabolic network. We then investigated the dynamic regulation by multiple control modules to balance the growth and production, so as to direct carbon sources for diol production. Finally, we proposed the challenges in the diol-biosynthesis process and suggested some potential methods to improve the diol-producing ability of the host.

Overcoming glutamate auxotrophy in Escherichia coli itaconate overproducer by the Weimberg pathway

Biosynthesis of itaconic acid occurs through decarboxylation of the TCA cycle intermediate cis-aconitate. Engineering of efficient itaconate producers often requires elimination of the highly active isocitrate dehydrogenase to conserve cis-aconitate, leading to 2-ketoglutarate auxotrophy in the producing strains. Supplementation of glutamate or complex protein hydrolysate then becomes necessary, often in large quantities, to support the high cell density desired during itaconate fermentation and adds to the production cost. Here, we present an alternative approach to overcome the glutamate auxotrophy in itaconate producers by synthetically introducing the Weimberg pathway from Burkholderia xenovorans for 2-ketoglutarate biosynthesis. Because of its independence from natural carbohydrate assimilation pathways in Escherichia coli, the Weimberg pathway is able to provide 2-ketoglutarate using xylose without compromising the carbon flux toward itaconate. With xylose concentration carefully tuned to minimize excess 2-ketoglutarate flux in the stationary phase, the final strain accumulated 20 g/L of itaconate in minimal medium from 18 g/L of xylose and 45 g/L of glycerol. Necessity of the recombinant Weimberg pathway for growth also allowed us to maintain multi-copy plasmids carrying in operon the itaconate-producing genes without addition of antibiotics. Use of the Weimberg pathway for growth restoration is applicable to other production systems with disrupted 2-ketoglutarate synthesis.

Microbial fuel cells using α-amylase-displaying Escherichia coli with starch as fuel

Escherichia coli JM109 (pGV3-SBA) can assimilate starch by fusing the starch-digesting enzyme α-amylase from Streptococcus bovis NRIC1535 to an OprI' lipoprotein anchor on the cell membrane. This study shows microbial fuel cells (MFCs) development using this recombinant type of E. coli and starch as fuel. We observed the current generation of MFCs with E. coli JM109 (pGV3-SBA) for 120 h. During this period, it consumed 7.1 g/L of starch. A mediator in the form of anthraquinone-2,6-disulfonic acid disodium salt at 0.2, 0.4, and 0.8 mM was added to the MFCs. The highest maximum-current density (271 mA/m²) and maximum-power density (29.3 mW/m²) performances occurred in the 0.4 mM mediator solution. Coulomb yields were calculated as 3.4%, 3.0%, and 3.5% in 1.0, 5.0, and 10.0 g/L of initial starch, respectively. The concentrations of acetic acid, succinic acid, fumaric acid, and ethanol as metabolites were determined. In particular, 38.3 mM of ethanol was produced from 7.1 g/L of starch. This study suggests the use of recombinant E. coli which can assimilate starch present in starch-fueled MFCs. Moreover, it proposes the possibility of gene recombination technology for using wide variety of biomass as fuel and improving MFC's performance.

Engineering Escherichia coli for Direct Production of 1,2-Propanediol and 1,3-Propanediol from Starch

Diols are versatile chemicals used for multiple manufacturing products. In some previous studies, Escherichia coli has been engineered to produce 1,2-propanediol (1,2-PDO) and 1,3-propanediol (1,3-PDO) from glucose. However, there are no reports on the direct production of these diols from starch instead of glucose as a substrate. In this study, we directly produced 1,2-PDO and 1,3-PDO from starch using E. coli engineered for expressing a heterologous α-amylase, along with the expression of 1,2-PDO and 1,3-PDO synthetic genes. For this, the recombinant plasmids, pVUB3-SBA harboring amyA gene for α-amylase production, pSR5 harboring pct, pduP, and yahK genes for 1,2-PDO production, and pSR8 harboring gpd1-gpp2, dhaB123, gdrAB, and dhaT genes for 1,3-PDO production, were constructed. Subsequently, E. coli BW25113 (ΔpflA) and BW25113 strains were transformed with pVUB3-SBA, pSR5, and/or pSR8. Using these transformants, direct production of 1,2-PDO and 1,3-PDO from starch was demonstrated under microaerobic condition. As a result, the maximum production titers of 1,2-PDO and 1,3-PDO from 1% glucose as a sole carbon source were 13 mg/L and 150 mg/L, respectively. The maximum production titers from 1% starch were similar levels (30 mg/L 1,2-PDO and 120 mg/L 1,3-PDO). These data indicate that starch can be an alternative carbon source for the production of 1,2-PDO and 1,3-PDO in engineered E. coli. This technology could simplify the upstream process of diol bioproduction.

Biomass-Derived Production of Itaconic Acid as a Building Block in Specialty Polymers

Biomass, the only source of renewable organic carbon on Earth, offers an efficient substrate for bio-based organic acid production as an alternative to the leading petrochemical industry based on non-renewable resources. Itaconic acid (IA) is one of the most important organic acids that can be obtained from lignocellulose biomass. IA, a 5-C dicarboxylic acid, is a promising platform chemical with extensive applications; therefore, it is included in the top 12 building block chemicals by the US Department of Energy. Biotechnologically, IA production can take place through fermentation with fungi like Aspergillus terreus and Ustilago maydis strains or with metabolically engineered bacteria like Escherichia coli and Corynebacterium glutamicum. Bio-based IA represents a feasible substitute for petrochemically produced acrylic acid, paints, varnishes, biodegradable polymers, and other different organic compounds. IA and its derivatives, due to their trifunctional structure, support the synthesis of a wide range of innovative polymers through crosslinking, with applications in special hydrogels for water decontamination, targeted drug delivery (especially in cancer treatment), smart nanohydrogels in food applications, coatings, and elastomers. The present review summarizes the latest research regarding major IA production pathways, metabolic engineering procedures, and the synthesis and applications of novel polymeric materials.

Synthetic Escherichia coli-Corynebacterium glutamicum consortia for l-lysine production from starch and sucrose

In the biorefinery concept renewable feedstocks are converted to a multitude of value-added compounds irrespective of seasonal or other variations of the complex biomass substrates. Conceptionally, this can be realized by specialized single microbial strains or by co-culturing various strain combinations. In the latter approach strains for substrate conversion and for product formation can be combined. This study addressed the construction of binary microbial consortia based on starch- and sucrose-based production of l-lysine and derived value-added compounds. A commensalism-based synthetic consortium for l-lysine production from sucrose was developed combining an l-lysine auxotrophic, naturally sucrose-negative E. coli strain with a C. glutamicum strain able to produce l-lysine that secretes fructose when grown with sucrose due to deletion of the fructose importer gene ptsF. Mutualistic synthetic consortia with an l-lysine auxotrophic, α-amylase secreting E. coli strain and naturally amylase-negative C. glutamicum strains was implemented for production of valuable fine chemicals from starch.

Production of itaconic acid by biotransformation of wheat bran hydrolysate with Aspergillus terreus CICC40205 mutant

The replacement of the carbon source in the microbial production of itaconic acid (IA) with economic alternatives has attracted significant attention. In this study, an Aspergillus terreus CICC40205 mutant was used to increase the IA titer and decrease the citric acid titer in the wheat bran hydrolysate compared with the parental strain. The results showed that the IA titer was increased by 33.4%, whereas the citric acid titer was decreased by 75.8%, and were in accordance with those of the improved pathway of co-metabolism of glucose and xylose according to the metabolic flux analysis. Additionally, the maximum IA titer obtained in a 7-L stirred tank was 49.65gL^-1±0.38gL^-1. Overall, A. terreus CICC40205 showed a great potential for the industrial production of IA through the biotransformation of the wheat bran hydrolysate.

Protein and metabolic engineering for the production of organic acids

Organic acids are natural metabolites of living organisms. They have been widely applied in the food, pharmaceutical, and bio-based materials industries. In recent years, biotechnological routes to organic acids production from renewable raw materials have been regarded as very promising approaches. In this review, we provide an overview of current developments in the production of organic acids using protein and metabolic engineering strategies. The organic acids include propionic acid, pyruvate, itaconic acid, succinic acid, fumaric acid, malic acid and citric acid. We also expect that rapid developments in the fields of systems biology and synthetic biology will accelerate protein and metabolic engineering for microbial organic acid production in the future.

Emerging biotechnologies for production of itaconic acid and its applications as a platform chemical

Recently, itaconic acid (IA), an unsaturated C5-dicarboxylic acid, has attracted much attention as a biobased building block chemical. It is produced industrially (>80 g L−1) from glucose by fermentation with Aspergillus terreus. The titer is low compared with citric acid production (>200 g L−1). This review summarizes the latest progress on enhancing the yield and productivity of IA production. IA biosynthesis involves the decarboxylation of the TCA cycle intermediate cis-aconitate through the action of cis-aconitate decarboxylase (CAD) enzyme encoded by the CadA gene in A. terreus. A number of recombinant microorganisms have been developed in an effort to overproduce it. IA is used as a monomer for production of superabsorbent polymer, resins, plastics, paints, and synthetic fibers. Its applications as a platform chemical are highlighted. It has a strong potential to replace petroleum-based methylacrylic acid in industry which will create a huge market for IA.

Challenges in the production of itaconic acid by metabolically engineered Escherichia coli

Metabolic engineering allows the production of a variety of high-value chemicals in heterologous hosts. For example, itaconic acid (IA) has been produced in several microorganisms, such as Escherichia coli, Aspergillus niger, and Synechocystis sp. through the expression of cis-aconitate decarboxylase gene (cad) from Aspergillus terreus. Recently, we showed that inactivation of the isocitrate dehydrogenase gene and overexpression of the aconitase gene dramatically enhanced the production levels of IA in E. coli expressing cad. Furthermore, we demonstrated that it is possible to produce IA directly from starch by engineered E. coli that additionally expresses the α-amylase gene from Streptococcus bovis. In this study, we sum up our findings regarding the challenges of IA production in E. coli.