Enhanced l-ornithine production by systematic manipulation of l-ornithine metabolism in engineered Corynebacterium glutamicum S9114

Sensory quality and Metabolomic fingerprinting of Lacticaseibacillus paracasei-derived fermented soymilk beverages: Impact of starter strain and storage

Few previous studies have concurrently evaluated the effects of different fermentation bacterial strains and storage durations on the characteristics of fermented soymilk beverages (FSBs). This study used Lacticaseibacillus paracasei to conduct systematic assessments and demonstrated that soy protein is the optimal ingredient for sensory evaluation. Both investigated strains (PC-01 and PC646) significantly enhanced the nutritional and flavor profiles of FSBs, introducing a range of bioactive metabolites absent in non-fermented soymilk. Throughout the storage period, a decline in pH and viable bacterial counts was observed, along with an increase in titratable acidity and stability. Moreover, the metabolomic structure and metabolite abundance varied considerably between the FSBs produced by the two strains, with the non-volatile components showing greater variation, whereas the storage duration predominantly influenced the volatile metabolite components. These insights highlight the critical roles of strain selection and storage duration in shaping the nutritional and sensory qualities of FSBs.

Copper Resistance Mechanism and Copper Response Genes in Corynebacterium crenatum

Heavy metal resistance mechanisms and heavy metal response genes are crucial for microbial utilization in heavy metal remediation. Here, Corynebacterium crenatum was proven to possess good tolerance in resistance to copper. Then, the transcriptomic responses to copper stress were investigated, and the vital pathways and genes involved in copper resistance of C. crenatum were determined. Based on transcriptome analysis results, a total of nine significantly upregulated DEGs related to metal ion transport were selected for further study. Among them, GY20_RS0100790 and GY20_RS0110535 belong to transcription factors, and GY20_RS0110270, GY20_RS0100790, and GY20_RS0110545 belong to copper-binding peptides. The two transcription factors were studied for the function of regulatory gene expression. The three copper-binding peptides were displayed on the C. crenatum surface for a copper adsorption test. Furthermore, the nine related metal ion transport genes were deleted to investigate the effect on growth in copper stress. This investigation provided the basis for utilizing C. crenatum in copper bioremediation.

Enhanced L-serine production by Corynebacterium glutamicum based on novel insights into L-serine exporters

The L-serine exporters ThrE and SerE play important roles in L-serine production by Corynebacterium glutamicum. Deletion of both thrE and serE decreased L-serine titer by 60%, suggesting the existence of other L-serine exporters. A comparative transcriptomics identified NCgl0254 and NCgl0255 as novel L-serine exporters. Further analysis of the contributions of ThrE, SerE, NCgl0254, and NCgl0255 found that SerE was the major L-serine exporter in C. glutamicum and these four L-serine exporters were responsible for 79.7% of L-serine export. Deletion of one L-serine exporter upregulated the transcription levels of the other three, which might be coursed by increased intracellular concentrations of L-serine. Overexpression of NCgl0254 and NCgl0255 increased L-serine titer by 20.8% in C. glutamicum A36, while overexpression of the four L-serine exporters increased L-serine production by 31.9% (41.1 g·L-1 ) in C. glutamicum A36. The identification of novel L-serine exporters in C. glutamicum will help to improve industrial production of L-serine.

Novel transporter screening technology for chemical production by microbial fermentation

In the fermentative production of compounds by using microorganisms, control of the transporter activity responsible for substrate uptake and product efflux, in addition to intracellular metabolic modification, is important from a productivity perspective. However, there has been little progress in analyses of the functions of microbial membrane transporters, and because of the difficulty in finding transporters that transport target compounds, only a few transporters have been put to practical use. Here, we constructed a Corynebacterium glutamicum-derived transporter expression library (CgTP-Express library) with the fusion partner gene mstX and used a peptide-feeding method with the dipeptide L-Ala-L-Ala to search for alanine exporters in the library. Among 39 genes in the library, five candidate alanine exporters (NCgl2533, NCgl2683, NCgl0986, NCgl0453, and NCgl0929) were found; expression of NCgl2533 increased the alanine concentration in cell culture. The CgTP-Express library was thus effective for finding a new transporter candidate.

Remodeling metabolism of Corynebacterium glutamicum for high-level dencichine production

Dencichine, a sought-after compound in the medical industry, requires a more efficient and sustainable production method than the current plant extraction process. This study successfully remodeled the metabolic pathway of Corynebacterium glutamicum to produce dencichine from the precursors of L-2,3-diaminopropionate (L-DAP) and oxalyl-coenzyme A. Firstly, a synthetic pathway for L-DAP was established by introducing exogenous enzymes ZmaU/ZmaV. This resulted in a production of 628 mg/L by overexpressing key genes and reducing the endogenous competitive pathway. Secondly, an oxalyl-CoA synthetic pathway was created through the enzymatic conversion of glyoxylate by introducing heterologous enzymes. Finally, with the integration of the exogenous enzyme BAHD, de novo synthesis of dencichine in C. glutamicum was achieved, and production reached 31.75 mg/L within 48-hour fermentation. This achievement represents the first successful biosynthesis of dencichine in C. glutamicum, offering a promising approach for natural product through microbial fermentation.

Enhancing Production of Medium-Chain-Length Polyhydroxyalkanoates from Pseudomonas sp. SG4502 by tac Enhancer Insertion

Pseudomonas sp. SG4502 screened from biodiesel fuel by-products can synthesize medium-chain-length polyhydroxyalkanoates (mcl-PHAs) using glycerol as a substrate. It contains a typical PHA class II synthase gene cluster. This study revealed two genetic engineering methods for improving the mcl-PHA accumulation capacity of Pseudomonas sp. SG4502. One way was to knock out the PHA-depolymerase phaZ gene, the other way was to insert a tac enhancer into the upstream of the phaC1/phaC2 genes. Yields of mcl-PHAs produced from 1% sodium octanoate by +(tac-phaC2) and ∆phaZ strains were enhanced by 53.8% and 23.1%, respectively, compared with those produced by the wild-type strain. The increase in mcl-PHA yield from +(tac-phaC2) and ∆phaZ was due to the transcriptional level of the phaC2 and phaZ genes, as determined by RT-qPCR (the carbon source was sodium octanoate). ¹H-NMR results showed that the synthesized products contained 3-hydroxyoctanoic acid (3HO), 3-hydroxydecanoic acid (3HD) and 3-hydroxydodecanoic acid (3HDD) units, which is consistent with those synthesized by the wild-type strain. The size-exclusion chromatography by GPC of mcl-PHAs from the (∆phaZ), +(tac-phaC1) and +(tac-phaC2) strains were 2.67, 2.52 and 2.60, respectively, all of which were lower than that of the wild-type strain (4.56). DSC analysis showed that the melting temperature of mcl-PHAs produced by recombinant strains ranged from 60 °C to 65 °C, which was lower than that of the wild-type strain. Finally, TG analysis showed that the decomposition temperature of mcl-PHAs synthesized by the (∆phaZ), +(tac-phaC1) and +(tac-phaC2) strains was 8.4 °C, 14.7 °C and 10.1 °C higher than that of the wild-type strain, respectively.

Bioprocess Engineering, Transcriptome, and Intermediate Metabolite Analysis of L-Serine High-Yielding Escherichia coli W3110

L-serine is widely used in the food, cosmetic, and pharmaceutical industries. However, the complicated metabolic network and regulatory mechanism of L-serine production lead to the suboptimal productivity of the direct fermentation of L-serine and limits its large-scale industrial production. In this study, a high-yield L-serine production Escherichia coli strain was constructed by a series of defined genetic modification methodologies. First, L-serine-mediated feedback inhibition was removed and L-serine biosynthetic pathway genes (serAfr, serC, and serB) associated with phosphoglycerate kinase (pgk) were overexpressed. Second, the L-serine conversion pathway was further examined by introducing a glyA mutation (K229G) and deleting other degrading enzymes based on the deletion of initial sdaA. Finally, the L-serine transport system was rationally engineered to reduce uptake and accelerate L-serine export. The optimally engineered strain produced 35 g/L L-serine with a productivity of 0.98 g/L/h and a yield of 0.42 g/g glucose in a 5-L fermenter, the highest productivity and yield of L-serine from glucose reported to date. Furthermore, transcriptome and intermediate metabolite of the high-yield L-serine production Escherichia coli strain were analyzed. The results demonstrated the regulatory mechanism of L-serine production is delicate, and that combined metabolic and bioprocess engineering strategies for L-serine producing strains can improve the productivity and yield.

Improvement in L-ornithine production from mannitol via transcriptome-guided genetic engineering in Corynebacterium glutamicum

BACKGROUND

L-Ornithine is an important medicinal intermediate that is mainly produced by microbial fermentation using glucose as the substrate. To avoid competition with human food resources, there is an urgent need to explore alternative carbon sources for L-ornithine production. In a previous study, we constructed an engineered strain, Corynebacterium glutamicum MTL13, which produces 54.56 g/L of L-ornithine from mannitol. However, compared with the titers produced using glucose as a substrate, the results are insufficient, and further improvement is required.

RESULTS

In this study, comparative transcriptome profiling of MTL01 cultivated with glucose or mannitol was performed to identify novel targets for engineering L-ornithine-producing strains. Guided by the transcriptome profiling results, we modulated the expression of qsuR (encoding a LysR-type regulator QsuR), prpC (encoding 2-methylcitrate synthase PrpC), pdxR (encoding a MocR-type regulator PdxR), acnR (encoding a TetR-type transcriptional regulator AcnR), CGS9114_RS08985 (encoding a hypothetical protein), and CGS9114_RS09730 (encoding a TetR/AcrR family transcriptional regulator), thereby generating the engineered strain MTL25 that can produce L-ornithine at a titer of 93.6 g/L, representing a 71.6% increase as compared with the parent strain MTL13 and the highest L-ornithine titer reported so far for C. glutamicum.

CONCLUSIONS

This study provides novel indirect genetic targets for enhancing L-ornithine accumulation on mannitol and lays a solid foundation for the biosynthesis of L-ornithine from marine macroalgae, which is farmed globally as a promising alternative feedstock.

Metabolic Engineering of Bacillus amyloliquefaciens to Efficiently Synthesize L-Ornithine From Inulin

Bacillus amyloliquefaciens is the dominant strain used to produce γ-polyglutamic acid from inulin, a non-grain raw material. B. amyloliquefaciens has a highly efficient tricarboxylic acid cycle metabolic flux and glutamate synthesis ability. These features confer great potential for the synthesis of glutamate derivatives. However, it is challenging to efficiently convert high levels of glutamate to a particular glutamate derivative. Here, we conducted a systematic study on the biosynthesis of L-ornithine by B. amyloliquefaciens using inulin. First, the polyglutamate synthase gene pgsBCA of B. amyloliquefaciens NB was knocked out to hinder polyglutamate synthesis, resulting in the accumulation of intracellular glutamate and ATP. Second, a modular engineering strategy was applied to coordinate the degradation pathway, precursor competition pathway, and L-ornithine synthesis pathway to prompt high levels of intracellular precursor glutamate for l-ornithine synthesis. In addition, the high-efficiency L-ornithine transporter was further screened and overexpressed to reduce the feedback inhibition of L-ornithine on the synthesis pathway. Combining these strategies with further fermentation optimizations, we achieved a final L-ornithine titer of 31.3 g/L from inulin. Overall, these strategies hold great potential for strengthening microbial synthesis of high value-added products derived from glutamate.

Reforming Nitrate Metabolism for Enhancing L-Arginine Production in Corynebacterium crenatum Under Oxygen Limitation

Various amino acids are widely manufactured using engineered bacteria. It is crucial to keep the dissolved oxygen at a certain level during fermentation, but accompanied by many disadvantages, such as high energy consumption, reactive oxygen species, and risk of phage infections. Thus, anaerobic production of amino acids is worth attempting. Nitrate respiration systems use nitrate as an electron acceptor under anoxic conditions, which is different from the metabolism of fermentation and can produce energy efficiently. Herein, we engineered Corynebacterium crenatum to enhance L-arginine production under anaerobic conditions through strengthening nitrate respiration and reforming nitrogen flux. The construction of mutant strain produced up to 3.84 g/L L-arginine under oxygen limitation with nitrate, and this value was 131.33% higher than that produced by the control strain under limited concentrations of oxygen without nitrate. Results could provide fundamental information for improving L-arginine production by metabolic engineering of C. crenatum under oxygen limitation.

Enhanced L-ornithine production from glucose and sucrose via manipulation of the fructose metabolic pathway in Corynebacterium glutamicum

L-Ornithine, an important non-essential amino acid, has considerable medicinal value in the treatment of complex liver diseases. Microbial fermentation strategies using robust engineered strains have remarkable potential for producing L-ornithine. We showed that glucose and sucrose co-utilization accumulate more L-ornithine in Corynebacterium glutamicum than glucose alone. Further manipulating the expression of intracellular fructose-1-phosphate kinase through the deletion of pfkB1resulted in the engineered strain C. glutamicum SO30 that produced 47.6 g/L of L-ornithine, which represents a 32.8% increase than the original strain C. glutamicum SO26 using glucose as substrate (35.88 g/L). Moreover, fed-batch cultivation of C. glutamicum SO30 in 5-L fermenters produced 78.0 g/L of L-ornithine, which was a 78.9% increase in yield compared with that produced by C. glutamicum SO26. These results showed that manipulating the fructose metabolic pathway increases L-ornithine accumulation and provides a reference for developing C. glutamicum to produce valuable metabolites.

Production of l-glutamate family amino acids in Corynebacterium glutamicum: Physiological mechanism, genetic modulation, and prospects

l-glutamate family amino acids (GFAAs), consisting of l-glutamate, l-arginine, l-citrulline, l-ornithine, l-proline, l-hydroxyproline, γ-aminobutyric acid, and 5-aminolevulinic acid, are widely applied in the food, pharmaceutical, cosmetic, and animal feed industries, accounting for billions of dollars of market activity. These GFAAs have many functions, including being protein constituents, maintaining the urea cycle, and providing precursors for the biosynthesis of pharmaceuticals. Currently, the production of GFAAs mainly depends on microbial fermentation using Corynebacterium glutamicum (including its related subspecies Corynebacterium crenatum), which is substantially engineered through multistep metabolic engineering strategies. This review systematically summarizes recent advances in the metabolic pathways, regulatory mechanisms, and metabolic engineering strategies for GFAA accumulation in C. glutamicum and C. crenatum, which provides insights into the recent progress in l-glutamate-derived chemical production.

Highly efficient biosynthesis of l-ornithine from mannitol by using recombinant Corynebacterium glutamicum

Mannitol is a promising six-carbon sugar alcohol that is widely found in macroalgae. The potential of mannitol as a renewable raw material is of interest due to the advantages of ocean farms. Herein, the biobased production of l-ornithine from mannitol was resoundingly demonstrated for the first time in engineered Corynebacterium glutamicum S9114 through the deletion of the mannitol repressor MtlR. By modulating the expression of mtlD and reinforcing the fructose metabolic pathway, we generated the strain MTL13 that produced 54.56 g/L of l-ornithine with a yield of 0.47 g/g on mannitol. These results illustrate the robust conversion from mannitol to l-ornithine using engineered Corynebacterium glutamicum, providing a reference for the biobased production of additional chemicals from mannitol.

Recent Progress on Chemical Production From Non-food Renewable Feedstocks Using Corynebacterium glutamicum

Due to the non-renewable nature of fossil fuels, microbial fermentation is considered a sustainable approach for chemical production using glucose, xylose, menthol, and other complex carbon sources represented by lignocellulosic biomass. Among these, xylose, methanol, arabinose, glycerol, and other alternative feedstocks have been identified as superior non-food sustainable carbon substrates that can be effectively developed for microbe-based bioproduction. Corynebacterium glutamicum is a model gram-positive bacterium that has been extensively engineered to produce amino acids and other chemicals. Recently, in order to reduce production costs and avoid competition for human food, C. glutamicum has also been engineered to broaden its substrate spectrum. Strengthening endogenous metabolic pathways or assembling heterologous ones enables C. glutamicum to rapidly catabolize a multitude of carbon sources. This review summarizes recent progress in metabolic engineering of C. glutamicum toward a broad substrate spectrum and diverse chemical production. In particularly, utilization of lignocellulosic biomass-derived complex hybrid carbon source represents the futural direction for non-food renewable feedstocks was discussed.

Metabolic engineering of Pseudomonas putida KT2440 for high-yield production of protocatechuic acid

Protocatechuic acid (PCA) has been widely utilized in conventional pharmaceutical, cosmetic and functional food industries. Currently, chemical synthesis and solvent extraction are the main methods for commercial production, indicating several disadvantages. In this study, we developed a method for the biosynthesis of PCA in Pseudomonas putida KT2440 in high yield. First, we developed constitutive promoters with different expression intensities for fine-tuned gene expression. Second, we improved the biosynthesis of "natural" PCA in P. putida KT2440 via multilevel metabolic engineering strategies: overexpression of rate-limiting enzymes, removal of negative regulators, attenuation of pathway competition, and enhancement of precursor supply. Finally, by further bioprocess engineering efforts, the best-producing strain reached a titer of 12.5 g/L PCA from glucose at 72 h in a shake flask and 21.7 g/L in fed-batch fermentation without antibiotic pressure. This was the highest PCA titer from glucose using metabolically engineered microbial cell factories reported to date.

l-arginine production in Corynebacterium glutamicum: manipulation and optimization of the metabolic process

As an important semi-essential amino acid, l-arginine is extensively used in the food and pharmaceutical fields. At present, l-arginine production depends on cost-effective, green, and sustainable microbial fermentation by using a renewable carbon source. To enhance its fermentative production, various metabolic engineering strategies have been employed, which provide valid paths for reducing the cost of l-arginine production. This review summarizes recent advances in molecular biology strategies for the optimization of l-arginine-producing strains, including manipulating the principal metabolic pathway, modulating the carbon metabolic pathway, improving the intracellular biosynthesis of cofactors and energy usage, manipulating the assimilation of ammonia, improving the transportation and membrane permeability, and performing biosensor-assisted high throughput screening, providing useful insight into the current state of l-arginine production.

Role of ClpB From Corynebacterium crenatum in Thermal Stress and Arginine Fermentation

ClpB, an ATP-dependent molecular chaperone, is involved in metabolic pathways and plays important roles in microorganisms under stress conditions. Metabolic pathways and stress resistance are important characteristics of industrially -relevant bacteria during fermentation. Nevertheless, ClpB-related observations have been rarely reported in industrially -relevant microorganisms. Herein, we found a homolog of ClpB from Corynebacterium crenatum. The amino acid sequence of ClpB was analyzed, and the recombinant ClpB protein was purified and characterized. The full function of ClpB requires DnaK as chaperone protein. For this reason, dnaK/clpB deletion mutants and the complemented strains were constructed to investigate the role of ClpB. The results showed that DnaK/ClpB is not essential for the survival of C. crenatum MT under pH and alcohol stresses. The ClpB-deficient or DnaK-deficient C. crenatum mutants showed weakened growth during thermal stress. In addition, the results demonstrated that deletion of the clpB gene affected glucose consumption and L-arginine, L-glutamate, and lactate production during fermentation.

Role of the ClpX from Corynebacterium crenatum involved in stress responses and energy metabolism

ClpX and ClpP are involved in many important functions, including stress responses and energy metabolism, in microorganisms. However, the ClpX and ClpP of microbes used in industrial scale have rarely been studied. Industrial bacterial fermentation experiences a variety of stresses, and energy metabolism is extremely important for industrial bacteria. Thus, the role played by the ClpX and ClpP of industrial bacteria in fermentation should be investigated. Most microorganisms have a single clpP gene, while Corynebacterium crenatum AS 1.542 possesses two clpPs. Herein, the clpX, clpP1, and clpP2 of C. crenatum were cloned, and its fusion protein was expressed and characterized. We also constructed clpX deletion mutant and complementation strain. Results indicate that ClpX serves an important function in thermal, pH, and ethanol stresses. It is also involved in NADPH synthesis and glucose consumption during fermentation.

CRISPR-Cpf1-Assisted Engineering of Corynebacterium glutamicum SNK118 for Enhanced L-Ornithine Production by NADP-Dependent Glyceraldehyde-3-Phosphate Dehydrogenase and NADH-Dependent Glutamate Dehydrogenase

Here, Corynebacterium glutamicum SNK118 was metabolically engineered for L-ornithine production through CRISPR-Cpf1-based genome manipulation and plasmid-based heterologous overexpression. Genes argF, argR, and ncgl2228 were deleted to block the degradation of L-ornithine, eliminate the global transcriptional repression, and alleviate the competitive branch pathway, respectively. Overexpression of CsgapC (NADP-dependent glyceraldehyde 3-phosphate dehydrogenases gene from Clostridium saccharobutylicum DSM 13864) and BsrocG (NADH-dependent glutamate dehydrogenase gene from Bacillus subtilis HB-1) resulted markedly increased ornithine biosynthesis. Eventually, the engineered strain KBJ11 (SNK118ΔargRΔargFΔncgl2228/pXMJ19-CsgapC-BsrocG) was constructed for L-ornithine overproduction. In fed-batch fermentation, L-ornithine of 88.26 g/L with productivity of 1.23 g/L/h (over 72 h) and yield of 0.414 g/g glucose was achieved by strain KBJ11 in a 10-L bioreactor. Our result represents the highest titer and yield of L-ornithine production by microbial fermentation. This study suggests that heterologous expression of CsgapC and BsrocG could promote L-ornithine production by C. glutamicum strains.

Recent Advances of L-ornithine Biosynthesis in Metabolically Engineered Corynebacterium glutamicum

L-ornithine, a valuable non-protein amino acid, has a wide range of applications in the pharmaceutical and food industries. Currently, microbial fermentation is a promising, sustainable, and environment-friendly method to produce L-ornithine. However, the industrial production capacity of L-ornithine by microbial fermentation is low and rarely meets the market demands. Various strategies have been employed to improve the L-ornithine production titers in the model strain, Corynebacterium glutamicum, which serves as a major indicator for improving the cost-effectiveness of L-ornithine production by microbial fermentation. This review focuses on the development of high L-ornithine-producing strains by metabolic engineering and reviews the recent advances in breeding strategies, such as reducing by-product formation, improving the supplementation of precursor glutamate, releasing negative regulation and negative feedback inhibition, increasing the supply of intracellular cofactors, modulating the central metabolic pathway, enhancing the transport system, and adaptive evolution for improving L-ornithine production.

Proteome analysis guided genetic engineering of Corynebacterium glutamicum S9114 for tween 40-triggered improvement in L-ornithine production

BACKGROUND

L-ornithine is a valuable amino acid with a wide range of applications in the pharmaceutical and food industries. However, the production of L-ornithine by fermentation cannot compete with other methods, because of the low titers produced with this technique. Development of fermentation techniques that result in a high yield of L-ornithine and efficient strategies for improving L-ornithine production are essential.

RESULTS

This study demonstrates that tween 40, a surfactant promoter of the production of glutamate and arginine, improves L-ornithine production titers in engineered C. glutamicum S9114. The intracellular metabolism under tween 40 triggered fermentation conditions was explored using a quantitative proteomic approach, identifying 48 up-regulated and 132 down-regulated proteins when compared with the control. Numerous proteins were identified as membrane proteins or functional proteins involved in the biosynthesis of the cell wall. Modulation of those genes revealed that the overexpression of CgS9114_09558 and the deletion of CgS9114_13845, CgS9114_02593, and CgS9114_02058 improved the production of L-ornithine in the engineered strain of C. glutamicum Orn8. The final strain with all the exploratory metabolic engineering manipulations produced 25.46 g/L of L-ornithine, and a yield of 0.303 g L-ornithine per g glucose, which was 30.6% higher than that produced by the original strain (19.5 g/L).

CONCLUSION

These results clearly demonstrate the positive effect of tween 40 addition on L-ornithine accumulation. Proteome analysis was performed to examine the impact of tween 40 addition on the physiological changes in C. glutamicum Orn8 and the results showed several promising modulation targets for developing L-ornithine-producing strains.

Utilization of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) for spectrochemical determination of l-ornithine: a multivariate optimization-assisted approach

A simple and highly sensitive univariate calibration strategy based on ultraviolet-visible (UV-Vis) absorption spectroscopy and assisted by multivariate screening and optimization was utilized for the determination of l-ornithine (l-ORN) as such and in the alimentary supplements. l-ORN, an OTC marketed amino acid, is widely used for bodybuilding and might be abused by athletes. A nucleophilic substitution reaction using 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) was the basis of the current investigation. Plackett-Burman design (PBD) and a response surface optimizer as screening and fine-tuning strategies, respectively, were instigated. Four numerical variables, reaction time (RT), temperature (Temp), pH and reagent volume (RV), and one categorical variable, the diluting solvent (DS), were considered. Absorbance of the yellow-colored adduct at 469 nm was the response studied. Pareto analysis, along with analysis of variance (ANOVA) were used to ascertain the significant variables (screening phase) and their domains (optimization phase). Response transformation and stepwise analysis were employed when necessary. Probability, cube and individual value plots were used to get an insight into the statistical impact of the variables tested. Multiple responses' optimization was performed using Derringer's function. Calibration curves were linear in the range of 5-50 μg mL-1. Job's technique of continuous variation showed that the stoichiometric ratio is 2 : 1 (NBD-Cl : l-ORN). The proposed technique was successfully applied to the dietary supplements of l-ORN, inferring no interference from adjuvants and excipients. Analytical performance of this technique was validated conforming to the ICH standards.

Metabolic engineering of Corynebacterium glutamicum S9114 to enhance the production of l-ornithine driven by glucose and xylose

l-ornithine, an important amino acid, is widely used in food and medicine industries. l-ornithine production mainly relies on microbial fermentation, which may not meet the industrial requirement owing to the poor fermentation ability of available strains. Herein, mscCG2 deletion, CgS9114_12202 (gdh2) overexpression and rational modulation in tricarboxylic acid cycle was firstly demonstrated to increase l-ornithine production in engineered Corynebacterium glutamicum S9114. By further modulate glucose utility result in strain SO26 that produced 38.5 g/L or 43.6 g/L of l-ornithine in shake flask and fed-batch fermentation, respectively. This was 25% higher than that of the original strain (30.8 g/L) and exhibits highest titer reported in shake-flask. Moreover, the incorporation of xylose pathway in the engineered strain resulted in the highest l-ornithine production titer (18.9 g/L) and yield (0.40 g/g xylose) with xylose substrate. These results illustrate the tremendous potential of the engineered strain C. glutamicum S9114 in l-ornithine production.

Improving the production of a novel antifungal alteramide B in Lysobacter enzymogenes OH11 by strengthening metabolic flux and precursor supply

Lysobacter enzymogenes OH11 is currently considered to be a novel biocontrol agent for various plant fungi diseases. At present, only heat-stable antifungal factor (HSAF) has been isolated and identified in culture, although other active compounds also showed antifungal activity. In the present study, a novel active compound, alteramide B (ATB), which exhibits broad-spectrum antagonistic activity against phytopathogenic fungi and oomycetes, was isolated. The genes responsible for ATB biosynthesis were also determined. In addition, a strain producing ATB with minimal HSAF production was successfully generated by redirecting metabolic flux, namely L. enzymogenes OH57. Furthermore, ATB production increased to 893.32 ± 15.57 mg/L through medium optimization and precursor supply strategy, which was 24.36-fold higher than that of 10% tryptic soy broth (36.67 ± 1.63 mg/L). Taken together, this study indicates ATB has great development value as a biopesticide because of its bioactivity and high production.

Optimization of ʟ-ornithine production in recombinant Corynebacterium glutamicum S9114 by cg3035 overexpression and manipulating the central metabolic pathway

Background

ʟ-Ornithine is an important amino acid with broad applications in pharmaceutical and food industries. Despite lagging ʟ-ornithine productivity and cost reduction, microbial fermentation is a promising route for sustainable ʟ-ornithine production and thus development of robust microbial strains with high stability and productivity is essential.

Results

Previously, we systematically developed a new strain, SO1 originate from Corynebacterium glutamicum S9114, for ʟ-ornithine production. In this work, overexpression of cg3035 encoding N-acetylglutamate synthase (NAGS) using a plasmid or by inserting a strong P_tac promoter into the chromosome was found to increase ʟ-ornithine production in the engineered C. glutamicum SO1. The genome-based cg3035 modulated strain was further engineered by attenuating the expression of pta and cat, inserting a strong P_eftu promoter in the upstream region of glycolytic enzymes such as pfkA, gap, and pyk, and redirecting carbon flux to the pentose phosphate pathway. The final strain with all the exploratory metabolic engineering manipulations produced 32.3 g/L of ʟ-ornithine, a yield of 0.395 g ornithine per g glucose, which was 35.7% higher than that produced by the original strain (23.8 g/L).

Conclusion

These results clearly demonstrated that enhancing the expression of NAGS promoted ʟ-ornithine production and provide a promising alternative systematic blueprint for developing ʟ-ornithine-producing C. glutamicum strains.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0940-9) contains supplementary material, which is available to authorized users.

Pathway engineering in Corynebacterium glutamicum S9114 for 5-aminolevulinic acid production

5-Aminolevulinic acid (ALA) is a non-protein amino acid with a significant potential for cancer treatment and plant stress resistance. Microbial fermentation has gradually replaced the traditional chemical-based method for ALA production, thus increasing the need for high-ALA-producing strains. In this study, we engineered the glutamate producing strain, Corynebacterium glutamicum S9114, for ALA production. To efficiently convert l-glutamate to ALA, hemA and hemL from Salmonella typhimurium and Escherichia coli were tandemly overexpressed. In addition, ncgl1221 encoding a glutamate transporter was deleted to block glutamate secretion and thus improve ALA production. Furthermore, the intrinsic ribosome-binding site (RBS) of hemB was replaced by a relatively weak RBS to reduce the conversion of ALA to porphyrin. Transcriptional and fermentation data confirmed that inactivation of lysE and putP reduced the conversion of glutamate to arginine and proline, which also contribute to ALA production. The final SA14 strain produced 895 mg/L concentration of ALA after 72 h incubation in a shake flask. This amount was 58-fold higher than that obtained by the parent strain C. glutamicum S9114. The results demonstrate the potential of C. glutamicum S9114 for efficient ALA production and provide new targets for the development of ALA-producing strains.

Ribosomal binding site sequences and promoters for expressing glutamate decarboxylase and producing γ-aminobutyrate in Corynebacterium glutamicum

Glutamate decarboxylase (GAD) converts l-glutamate (Glu) into γ-aminobutyric acid (GABA). Corynebacterium glutamicum that expresses exogenous GAD gene, gadB2 or gadB1, can synthesize GABA from its own produced Glu. To enhance GABA production in C. glutamicum, ribosomal binding site (RBS) sequence and promoter were searched and optimized for increasing the expression efficiency of gadB2. R4 exhibited the highest strength among RBS sequences tested, with 6 nt the optimal aligned spacing (AS) between RBS and start codon. This combination of RBS sequence and AS contributed to gadB2 expression, increased GAD activity by 156% and GABA production by 82% compared to normal strong RBS and AS combination. Then, a series of native promoters were selected for transcribing gadB2 under optimal RBS and AS combination. P_dnaK, P_dtsR, P_odhI and P_clgR expressed gadB2 and produced GABA as effectively as widely applied P_tuf and P_cspB promoters and more effectively than P_sod promoter. However, each native promoter did not work as well as the synthetic strong promoter P_tacM, which produced 20.2 ± 0.3 g/L GABA. Even with prolonged length and bicistronic architecture, the strength of P_dnaK did not enhance. Finally, gadB2 and mutant gadB1 were co-expressed under the optimal promoter and RBS combination, thus converted Glu into GABA completely and improved GABA production to more than 25 g/L. This study provides useful promoters and RBS sequences for gene expression in C. glutamicum.

Model-based reconstruction of synthetic promoter library in Corynebacterium glutamicum

OBJECTIVE

To develop an efficient synthetic promoter library for fine-tuned expression of target genes in Corynebacterium glutamicum.

RESULTS

A synthetic promoter library for C. glutamicum was developed based on conserved sequences of the - 10 and - 35 regions. The synthetic promoter library covered a wide range of strengths, ranging from 1 to 193% of the tac promoter. 68 promoters were selected and sequenced for correlation analysis between promoter sequence and strength with a statistical model. A new promoter library was further reconstructed with improved promoter strength and coverage based on the results of correlation analysis. Tandem promoter P70 was finally constructed with increased strength by 121% over the tac promoter. The promoter library developed in this study showed a great potential for applications in metabolic engineering and synthetic biology for the optimization of metabolic networks.

CONCLUSIONS

To the best of our knowledge, this is the first reconstruction of synthetic promoter library based on statistical analysis of C. glutamicum.

Improvement of L-ornithine production by attenuation of argF in engineered Corynebacterium glutamicum S9114

l-Ornithine, a non-essential amino acid, has enormous industrial applications in food, pharmaceutical, and chemical industries. Currently, l-ornithine production is focused on microorganism fermentation using Escherichia coli or Corynebacterium glutamicum. In C. glutamicum, development of high l-ornithine producing C. glutamicum was achieved by deletion of argF, but was accompanied by growth deficiency and arginine auxotrophy. l-Arginine has been routinely added to solve this problem; however, this increases production cost and causes feedback inhibition of N-acetyl-l-glutamate kinase activity. To avoid the drawbacks of growth disturbance due to disruption of ArgF, strategies were adopted to attenuate its expression. Firstly, ribosome binding site substitution and start codon replacement were introduced to construct recombinant C. glutamiucm strains, which resulted in an undesirable l-ornithine production titer. Then, we inserted a terminator (rrnB) between argD and argF, which significantly improved l-ornithine production and relieved growth disturbance. Transcription analysis confirmed that a terminator can be used to downregulate expression of argF and simultaneously improve the transcriptional level of genes in front of argF. Using disparate terminators to attenuate expression of argF, an optimal strain (CO-9) with a T4 terminator produced 6.1 g/L of l-ornithine, which is 42.8% higher than that produced by strain CO-1, and is 11.2-fold higher than that of the parent CO strain. Insertion of terminators with gradient termination intensity can be a stable and powerful method to exert precise control of the expression level of argF in the development of l-ornithine producing strains, with potential applications in metabolic engineering and synthetic biology.