Succinic acid production and CO2 fixation using a metabolically engineered Escherichia coli in a bioreactor equipped with a self-inducing agitator

Effect of adaptive laboratory evolution of engineered Escherichia coli in acetate on the biosynthesis of succinic acid from glucose in two-stage cultivation

Escherichia coli MLB (MG1655 ΔpflB ΔldhA), which can hardly grow on glucose with little succinate accumulation under anaerobic conditions. Two-stage fermentation is a fermentation in which the first stage is used for cell growth and the second stage is used for product production. The ability of glucose consumption and succinate production of MLB under anaerobic conditions can be improved significantly by using acetate as the solo carbon source under aerobic condition during the two-stage fermentation. Then, the adaptive laboratory evolution (ALE) of growing on acetate was applied here. We assumed that the activities of succinate production related enzymes might be further improved in this study. E. coli MLB46-05 evolved from MLB and it had an improved growth phenotype on acetate. Interestingly, in MLB46-05, the yield and tolerance of succinic acid in the anaerobic condition of two-stage fermentation were improved significantly. According to transcriptome analysis, upregulation of the glyoxylate cycle and the activity of stress regulatory factors are the possible reasons for the elevated yield. And the increased tolerance to acetate made it more tolerant to high concentrations of glucose and succinate. Finally, strain MLB46-05 produced 111 g/L of succinic acid with a product yield of 0.74 g/g glucose. SYNOPSIS.

Self-inducing Reactors for Bioengineering

Packed tower reactors, mechanically stirred reactors, airlift reactors, and gas-self-inducing reactors are frequently utilized among the various types of reactors. Self-inducing reactors exhibit notable advantages owing to their simple structure, effective gas-liquid intermixing, and low energy requirements, rendering them highly suitable for bioengineering endeavors. The purpose of this analysis is to shed light on the use of self-inducing reactors in bioengineering by examining the following five parameters: critical speed, suction rate, volumetric mass transfer coefficient, power characteristics, and gas hold-up. Through a comprehensive analysis of the advancements achieved in these domains, it is possible to determine the challenges and opportunities that lie ahead in the realm of bioengineering.

Bio-conversion of CO2 into biofuels and other value-added chemicals via metabolic engineering

Carbon dioxide (CO₂) occurs naturally in the atmosphere as a trace gas, which is produced naturally as well as by anthropogenic activities. CO₂ is a readily available source of carbon that in principle can be used as a raw material for the synthesis of valuable products. The autotrophic organisms are naturally equipped to convert CO₂ into biomass by obtaining energy from sunlight or inorganic electron donors. This autotrophic CO₂ fixation has been exploited in biotechnology, and microbial cell factories have been metabolically engineered to convert CO₂ into biofuels and other value-added bio-based chemicals. A variety of metabolic engineering efforts for CO₂ fixation ranging from basic copy, paste, and fine-tuning approaches to engineering and testing of novel synthetic CO₂ fixing pathways have been demonstrated. In this paper, we review the current advances and innovations in metabolic engineering for bio-conversion of CO₂ into bio biofuels and other value-added bio-based chemicals.

Two-Stage Crystallization Combining Direct Succinimide Synthesis for the Recovery of Succinic Acid From Fermentation Broth

Succinic acid is an important chemical and raw material widely used in medicine, food, biodegradable materials, fine chemicals, and other industrial fields. However, traditional methods for purifying succinic acid from fermentation broth are costly, poorly efficient, and harmful to the environment. In this study, an efficient method for purifying succinic acid from the fermentation broth of Escherichia coli NZN111 was developed through crystallization and co-crystallization with urea. First, the filtrate was collected by filtering the fermentation broth, and pH was adjusted to 2.0 by supplementing sulfuric acid. Crystallization was carried out at 8°C for 4 h to obtain succinic acid crystals. The recovery rate and purity of succinic acid were 73.4% and over 99%, respectively. Then, urea was added to the remaining solution with a mass ratio of urea to residual succinic acid of 4:1 (m urea /m SA ). The second crystallization was carried out at pH 2 and 4°C for 12 h to obtain succinic acid-urea co-crystal. The recovery rate of succinic acid residue was 92.0%. The succinic acid-urea crystal was further mixed with phosphorous acid (4.2% of the mass of succinic acid co-crystal) and maintained at 195°C for 6 h to synthesize succinimide, and the yield was >80%. This novel and efficient purification process was characterized by the significantly reduced urea consumption, and high succinic acid recovery (totally 95%), and high succinimide synthesis yield (80%). Thus, this study potentially provided a novel and efficient strategy for the industrial production of succinic acid and succinimide.

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.

Efficient anaerobic production of succinate from glycerol in engineered Escherichia coli by using dual carbon sources and limiting oxygen supply in preceding aerobic culture

Glycerol is an important resource for production of value-added bioproducts due to its large availability from the biodiesel industry as a by-product. In this study, two metabolic regulation strategies were applied in the aerobic stage of a two-stage fermentation to achieve high metabolic capacities of the pflB ldhA double mutant Escherichia coli strain overexpressing phosphoenolpyruvate carboxykinase (PCK) in the subsequent anaerobic stage: use of acetate as a co-carbon source of glycerol and restriction of oxygen supply in the PCK induction period. The succinate concentration achieved 926.7mM with a yield of 0.91mol/mol during the anaerobic stage of fermentation in a 1.5-L reactor. qRT-PCR indicated that the two strategies enhanced transcription of genes related with glycerol metabolism and succinate production. Our results showed this metabolically engineered E. coli strain has a great potential in producing succinate using glycerol as carbon source.

Production of Succinate from Acetate by Metabolically Engineered Escherichia coli

Acetate, a major component of industrial biological wastewater and of lignocellulosic biomass hydrolysate, could potentially be a less costly alternative carbon source. Here we engineered Escherichia coli MG1655 strain for succinate production from acetate as the sole carbon source. Strategies of metabolic engineering included the blockage of the TCA cycle, redirection of the gluconeogenesis pathway, and enhancement of the glyoxylate shunt. The engineered strain MG03 featuring the deletion of genes: succinate dehydrogenase (sdhAB), isocitrate lyase regulator (iclR), and malic enzymes (maeB) accumulated 6.86 mM of succinate in 72 h. MG03(pTrc99a-gltA) overexpressing citrate synthase (gltA) accumulated 16.45 mM of succinate and the yield reached 0.46 mol/mol, about 92% of the maximum theoretical yield. Resting-cell was adopted for the conversion of acetate to succinate, and the highest concentration of succinate achieved 61.7 mM.

Zero-growth bioprocesses: A challenge for microbial production strains and bioprocess engineering

Microbial fermentation of renewable feedstocks is an established technology in industrial biotechnology. Besides strict aerobic or anaerobic modes of operation, novel innovative and industrially applicable fermentation processes were developed connecting the advantages of aerobic and anaerobic conditions in a combined production approach. As a consequence, rapid aerobic biomass formation to high cell densities and subsequent anaerobic high-yield and zero-growth production is realized. Following this strategy, bioprocesses operating with substantial overall yield and productivity can be obtained. Here, we summarize the current knowledge and achievements in such microbial zero-growth production processes and pinpoint to challenges due to the complex adaptation of the cellular metabolism during the cell's passage from aerobiosis to anaerobiosis.

Enhanced succinate production from glycerol by engineered Escherichia coli strains

In this study, an engineered strain Escherichia coli MLB (ldhA(-)pflB(-)) was constructed for production of succinate from glycerol. The succinate yield was 0.37mol/mol in anaerobic culture, however, the growth and glycerol consumption rates were very slow, resulting in a low succinate level. Two-stage fermentation was performed in flasks, and the succinate yield reached 0.93mol/mol, but the succinate titer was still low. Hence, overexpression of malate dehydrogenase, malic enzyme, phosphoenolpyruvate (PEP) carboxylase and PEP carboxykinase (PCK) from E. coli, and pyruvate carboxylase from Corynebacterium glutamicum in MLB was investigated for improving succinate production. Overexpression of PCK resulted in remarkable enhancement of glycerol consumption and succinate production. In flask experiments, the succinate concentration reached 118.1mM, and in a 1.5-L bioreactor the succinate concentration further increased to 360.2mM. The highest succinate yield achieved 0.93mol/mol, which was 93% of the theoretical yield, in the anaerobic stage.

Efficient carbon dioxide utilization and simultaneous hydrogen enrichment from off-gas of acetone-butanol-ethanol fermentation by succinic acid producing Escherichia coli

The off-gas from acetone-butanol-ethanol (ABE) fermentation was firstly used to be CO2 source (co-substrate) for succinic acid production. The optimum ratio of H2/CO2 indicated higher CO2 partial pressures with presence of H2 could enhance C4 pathway flux and reductive product productivity. Moreover, when an inner recycling bioreactor was used for CO2 recycling at a high total pressure (0.2Mpa), a maximum succinic acid concentration of 65.7g·L(-1) was obtained, and a productivity of 0.76g·L(-1)·h(-1) and a high yield of 0.86g·g(-1) glucose were achieved. Furthermore, the hydrogen content was simultaneously enriched to 92.7%. These results showed one successful attempt to reuse the off-gas of ABE fermentation which can be an attractive CO2 source for succinic acid production.

Enhanced succinic acid production from corncob hydrolysate by microbial electrolysis cells

In this study, Actinobacillus succinogenes NJ113 microbial electrolysis cells (MECs) were used to enhance the reducing power responsible for succinic acid production from corncob hydrolysate. During corncob hydrolysate fermentation, electric MECs resulted in a 1.31-fold increase in succinic acid production and a 1.33-fold increase in the reducing power compared with those in non-electric MECs. When the hydrolysate was detoxified by combining Ca(OH)2, NaOH, and activated carbon, succinic acid production increased from 3.47 to 6.95 g/l. Using a constant potential of -1.8 V further increased succinic acid production to 7.18 g/l. A total of 18.09 g/l of succinic acid and a yield of 0.60 g/g total sugar were obtained after a 60-h fermentation when NaOH was used as a pH regulator. The improved succinic acid yield from corncob hydrolysate fermentation using A. succinogenes NJ113 in electric MECs demonstrates the great potential of using biomass as a feedstock to cost-effectively produce succinate.

Biocatalysis for the application of CO2 as a chemical feedstock

Biocatalysts, capable of efficiently transforming CO2 into other more reduced forms of carbon, offer sustainable alternatives to current oxidative technologies that rely on diminishing natural fossil-fuel deposits. Enzymes that catalyse CO2 fixation steps in carbon assimilation pathways are promising catalysts for the sustainable transformation of this safe and renewable feedstock into central metabolites. These may be further converted into a wide range of fuels and commodity chemicals, through the multitude of known enzymatic reactions. The required reducing equivalents for the net carbon reductions may be drawn from solar energy, electricity or chemical oxidation, and delivered in vitro or through cellular mechanisms, while enzyme catalysis lowers the activation barriers of the CO2 transformations to make them more energy efficient. The development of technologies that treat CO2-transforming enzymes and other cellular components as modules that may be assembled into synthetic reaction circuits will facilitate the use of CO2 as a renewable chemical feedstock, greatly enabling a sustainable carbon bio-economy.

Techno-economics of carbon preserving butanol production using a combined fermentative and catalytic approach

This paper presents a novel process for n-butanol production which combines a fermentation consuming carbon dioxide (succinic acid fermentation) with subsequent catalytic reduction steps to add hydrogen to form butanol. Process simulations in Aspen Plus have been the basis for the techno-economic analyses performed. The overall economy for the novel process cannot be justified, as production of succinic acid by fermentation is too costly. Though, succinic acid price is expected to drop drastically in a near future. By fully integrating the succinic acid fermentation with the catalytic conversion the need for costly recovery operations could be reduced. The hybrid process would need 22% less raw material than the butanol fermentation at a succinic acid fermentation yield of 0.7g/g substrate. Additionally, a carbon dioxide fixation of up to 13ktonnes could be achieved at a plant with an annual butanol production of 10ktonnes.

Repetitive succinic acid production from lignocellulose hydrolysates by enhancement of ATP supply in metabolically engineered Escherichia coli

In this study, repetitive production of succinic acid from lignocellulose hydrolysates by enhancement of ATP supply in metabolically engineered E. coli is reported. Escherichia coli BA305, a pflB, ldhA, ppc, and ptsG deletion strain overexpressing ATP-forming phosphoenolpyruvate (PEP) carboxykinase (PEPCK), produced a final succinic acid concentration of 83 g L(-1) with a high yield of 0.87 g g(-1) total sugar in 36 h of three repetitive fermentations of sugarcane bagasse hydrolysate. Furthermore, simultaneous consumption of glucose and xylose was achieved, and the specific productivity and yield of succinic acid were almost maintained constant during the repetitive fermentations.

A novel process for recovery of fermentation-derived succinic acid: process design and economic analysis

Recovery and purification of organic acids produced in fermentation constitutes a significant fraction of total production cost. In this paper, the design and economic analysis of a process to recover succinic acid (SA) via dissolution and acidification of succinate salts in ethanol, followed by reactive distillation to form succinate esters, is presented. Process simulation was performed for a range of plant capacities (13-55 million kg/yr SA) and SA fermentation titers (50-100 kg/m(3)). Economics were evaluated for a recovery system installed within an existing fermentation facility producing succinate salts at a cost of $0.66/kg SA. For a SA processing capacity of 54.9 million kg/yr and a titer of 100 kg/m(3) SA, the model predicts a capital investment of $75 million and a net processing cost of $1.85 per kg SA. Required selling price of diethyl succinate for a 30% annual return on investment is $1.57 per kg.

Succinate production by metabolically engineered Escherichia coli using sugarcane bagasse hydrolysate as the carbon source

Efficient biosynthesis of succinate from a renewable biomass resource by engineered Escherichia coli is reported in this paper. Fermentation of sugarcane bagasse hydrolysate by engineered E. coli BA204, a pflB, ldhA, and ppc deletion strain overexpressing the ATP-forming phosphoenolpyruvate carboxykinase from Bacillus subtilis 168, produced a final succinate concentration of 15.85 g L(-1) with a high yield of 0.89 g L(-1) total sugar under anaerobic conditions. During dual-phase fermentations, initial aerobic growth facilitated subsequent anaerobic succinate production, with a final succinate concentration of 18.88 g L(-1) and a yield of 0.96 g g(-1) total sugar after 24 h of anaerobic fermentation. The high succinate yield from sugarcane bagasse hydrolysate demonstrated a great potential application of renewable biomass as a feedstock for the economical production of succinate using metabolically engineered E. coli.