Site-directed mutagenesis and feedback-resistant N-acetyl-L-glutamate kinase (NAGK) increase Corynebacterium crenatum L-arginine production

Insights into the Early Steps of the Symbiotic Interaction between Soybean (Glycine max) and Sinorhizobium fredii Symbiosis Using Transcriptome, Small RNA, and Degradome Sequencing

Symbiotic nitrogen fixation carried out by the soybean-rhizobia symbiosis increases soybean yield and reduces the amount of nitrogen fertilizer that has been applied. MicroRNAs (miRNAs) are crucial in plant growth and development, prompting an investigation into their role in the symbiotic interaction of soybean with partner rhizobia. Through integrated small RNA, transcriptome, and degradome sequencing analysis, 1215 known miRNAs, 314 of them conserved, and 187 novel miRNAs were identified, with 44 differentially expressed miRNAs in soybean roots inoculated with Sinorhizobium fredii HH103 and a ttsI mutant. The study unveiled that the known miRNA gma-MIR398a-p5 was downregulated in the presence of the ttsI mutation, while the target gene of gma-MIR398a-p5, Glyma.06G007500, associated with nitrogen metabolism, was upregulated. The results of this study offer insights for breeding high-efficiency nitrogen-fixing soybean varieties, enhancing crop yield and quality.

Insight into de-regulation of amino acid feedback inhibition: a focus on structure analysis method

Regulation of amino acid's biosynthetic pathway is of significant importance to maintain homeostasis and cell functions. Amino acids regulate their biosynthetic pathway by end-product feedback inhibition of enzymes catalyzing committed steps of a pathway. Discovery of new feedback resistant enzyme variants to enhance industrial production of amino acids is a key objective in industrial biotechnology. Deregulation of feedback inhibition has been achieved for various enzymes using in vitro and in silico mutagenesis techniques. As enzyme's function, its substrate binding capacity, catalysis activity, regulation and stability are dependent on its structural characteristics, here, we provide detailed structural analysis of all feedback sensitive enzyme targets in amino acid biosynthetic pathways. Current review summarizes information regarding structural characteristics of various enzyme targets and effect of mutations on their structures and functions especially in terms of deregulation of feedback inhibition. Furthermore, applicability of various experimental as well as computational mutagenesis techniques to accomplish feedback resistance has also been discussed in detail to have an insight into various aspects of research work reported in this particular field of study.

Development of a 2-pyrrolidone biosynthetic pathway in Corynebacterium glutamicum by engineering an acetyl-CoA balance route

2-Pyrrolidone is widely used in the textile and pharmaceutical industries. Here, we established a 2-pyrrolidone biosynthesis pathway in Corynebacterium glutamicum, by expressing glutamate decarboxylase (Gad) mutant and β-alanine CoA transferase (Act) which activates spontaneous dehydration cyclization of GABA to form 2-pyrrolidone. Also, the 5' untranslated regions (UTR) strategy was used to increase the expression of protein. Furthermore, considering the importance of acetyl-CoA in the 2-pyrrolidone synthesis pathway, the acetyl-CoA synthetase (acsA) gene was introduced to convert acetate into acetyl-CoA thus achieving the recyclability of the economy. Finally, the fed-batch fermentation of the final strain in a 5 L bioreactor produced 10.5 g/L 2-pyrrolidone within 78 h, which increased by 42.5% by altering the level of gene expression. This is the first time to build the basic chemical 2-pyrrolidone from glucose in one step in C. glutamicum.

High-level production of the agmatine in engineered Corynebacterium crenatum with the inhibition-releasing arginine decarboxylase

Background

Agmatine is a member of biogenic amines and is an important medicine which is widely used to regulate body balance and neuroprotective effects. At present, the industrial production of agmatine mainly depends on the chemical method, but it is often accompanied by problems including cumbersome processes, harsh reaction conditions, toxic substances production and heavy environmental pollution. Therefore, to tackle the above issues, arginine decarboxylase was overexpressed heterologously and rationally designed in Corynebacterium crenatum to produce agmatine from glucose by one-step fermentation.

Results

In this study, we report the development in the Generally Regarded as Safe (GRAS) l-arginine-overproducing C. crenatum for high-titer agmatine biosynthesis through overexpressing arginine decarboxylase based on metabolic engineering. Then, arginine decarboxylase was mutated to release feedback inhibition and improve catalytic activity. Subsequently, the specific enzyme activity and half-inhibitory concentration of I534D mutant were increased 35.7% and 48.1%, respectively. The agmatine production of the whole-cell bioconversion with AGM3 was increased by 19.3% than the AGM2. Finally, 45.26 g/L agmatine with the yield of 0.31 g/g glucose was achieved by one-step fermentation of the engineered C. crenatum with overexpression of speAI534D.

Conclusions

The engineered C. crenatum strain AGM3 in this work was proved as an efficient microbial cell factory for the industrial fermentative production of agmatine. Based on the insights from this work, further producing other valuable biochemicals derived from l-arginine by Corynebacterium crenatum is feasible.

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.

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.

Synthetic engineering of Corynebacterium crenatum to selectively produce acetoin or 2,3-butanediol by one step bioconversion method

BACKGROUND

Acetoin (AC) and 2,3-butanediol (2,3-BD) as highly promising bio-based platform chemicals have received more attentions due to their wide range of applications. However, the non-efficient substrate conversion and mutually transition between AC and 2,3-BD in their natural producing strains not only led to a low selectivity but also increase the difficulty of downstream purification. Therefore, synthetic engineering of more suitable strains should be a reliable strategy to selectively produce AC and 2,3-BD, respectively.

RESULTS

In this study, the respective AC (alsS and alsD) and 2,3-BD biosynthesis pathway genes (alsS, alsD, and bdhA) derived from Bacillus subtilis 168 were successfully expressed in non-natural AC and 2,3-BD producing Corynebacterium crenatum, and generated recombinant strains, C. crenatum SD and C. crenatum SDA, were proved to produce 9.86 g L-1 of AC and 17.08 g L-1 of 2,3-BD, respectively. To further increase AC and 2,3-BD selectivity, the AC reducing gene (butA) and lactic acid dehydrogenase gene (ldh) in C. crenatum were then deleted. Finally, C. crenatumΔbutAΔldh SD produced 76.93 g L-1 AC in one-step biocatalysis with the yield of 0.67 mol mol-1. Meanwhile, after eliminating the lactic acid production and enhancing 2,3-butanediol dehydrogenase activity, C. crenatumΔldh SDA synthesized 88.83 g L-1 of 2,3-BD with the yield of 0.80 mol mol-1.

CONCLUSIONS

The synthetically engineered C. crenatumΔbutAΔldh SD and C. crenatumΔldh SDA in this study were proved as an efficient microbial cell factory for selective AC and 2,3-BD production. Based on the insights from this study, further synthetic engineering of C. crenatum for AC and 2,3-BD production is suggested.

Enhancement of L-arginine production by increasing ammonium uptake in an AmtR-deficient Corynebacterium crenatum mutant

L-Arginine is an important amino acid with extensive application in the food and pharmaceutical industries. The efficiency of nitrogen uptake and assimilation by organisms is extremely important for L-arginine production. In this study, a strain engineering strategy focusing on upregulate intracellular nitrogen metabolism in Corynebacterium crenatum for L-arginine production was conducted. Firstly, the nitrogen metabolism global transcriptional regulator AmtR was deleted, which has demonstrated the beneficial effect on L-arginine production. Subsequently, this strain was engineered by overexpressing the ammonium transporter AmtB to increase the uptake of NH₄⁺ and L-arginine production. To overcome the drawbacks of using a plasmid to express amtB, P_tac, a strong promoter with amtB gene fragment, was integrated into the amtR region on the chromosome in the Corynebacterium crenatum/ΔamtR. The final strain results in L-arginine production at a titer of 60.9 g/L, which was 35.14% higher than that produced by C. crenatum SYPA5-5.

Insight of Genus Corynebacterium: Ascertaining the Role of Pathogenic and Non-pathogenic Species

This review gathers recent information about genomic and transcriptomic studies in the Corynebacterium genus, exploring, for example, prediction of pathogenicity islands and stress response in different pathogenic and non-pathogenic species. In addition, is described several phylogeny studies to Corynebacterium, exploring since the identification of species until biological speciation in one species belonging to the genus Corynebacterium. Important concepts associated with virulence highlighting the role of Pld protein and Tox gene. The adhesion, characteristic of virulence factor, was described using the sortase mechanism that is associated to anchorage to the cell wall. In addition, survival inside the host cell and some diseases, were too addressed for pathogenic corynebacteria, while important biochemical pathways and biotechnological applications retain the focus of this review for non-pathogenic corynebacteria. Concluding, this review broadly explores characteristics in genus Corynebacterium showing to have strong relevance inside the medical, veterinary, and biotechnology field.

Conformational dynamics play important roles upon the function of N-acetylglutamate kinase

N-acetylglutamate kinase (NAGK) catalyzes the phosphorylation of N-acetylglutamate. In many bacteria, NAGK catalysis is the rate controlling step in the L-arginine biosynthesis pathway from glutamate to L-arginine and is allosterically inhibited by L-arginine. Many data show that conformational dynamics of NAGKs are essential for their function. The demonstration of the conformational mechanism provides a potential way to improve the yield of arginine. Due to the lack of NAGK catalysis step in arginine synthesis route of mammals, the elucidation of the dynamic mechanism can also provide a way to design a new antivirus drug. This paper reviews how the dynamics affect the activity of NAGKs and are controlled by the effectors. X-ray crystallography and modeling data have shown that in NAGKs, the structural elements required for inhibitor and substrate binding, catalysis and product release, are highly mobile. It is possible to eliminate the inhibition of the arginine and/or block the synthesis of arginine by disturbing the flexibility of the NAGKs. Amino acid kinase family is thought to share some common dynamic features; the flexible structural elements of NAGKs have been identified, but the details of the dynamics and the signal transfer pathways are yet to be elucidated.

Reengineering of the feedback-inhibition enzyme N-acetyl-l-glutamate kinase to enhance l-arginine production in Corynebacterium crenatum

N-acetyl-l-glutamate kinase (NAGK) catalyzes the second step of l-arginine biosynthesis and is inhibited by l-arginine in Corynebacterium crenatum. To ascertain the basis for the arginine sensitivity of CcNAGK, residue E19 which located at the entrance of the Arginine-ring was subjected to site-saturated mutagenesis and we successfully illustrated the inhibition-resistant mechanism. Typically, the E19Y mutant displayed the greatest deregulation of l-arginine feedback inhibition. An equally important strategy is to improve the catalytic activity and thermostability of CcNAGK. For further strain improvement, we used site-directed mutagenesis to identify mutations that improve CcNAGK. Results identified variants I74V, F91H and K234T display higher specific activity and thermostability. The l-arginine yield and productivity of the recombinant strain C. crenatum SYPA-EH3 (which possesses a combination of all four mutant sites, E19Y/I74V/F91H/K234T) reached 61.2 and 0.638 g/L/h, respectively, after 96 h in 5 L bioreactor fermentation, an increase of approximately 41.8% compared with the initial strain.

Improvement of the ammonia assimilation for enhancing L-arginine production of Corynebacterium crenatum

There are four nitrogen atoms in L-arginine molecule and the nitrogen content is 32.1%. By now, metabolic engineering for L-arginine production strain improvement was focused on carbon flux optimization. In previous work, we obtained an L-arginine-producing Corynebacterium crenatum SDNN403 (ARG) through screening and mutation breeding. In this paper, a strain engineering strategy focusing on nitrogen supply and ammonium assimilation for L-arginine production was performed. Firstly, the effects of nitrogen atom donor (L-glutamate, L-glutamine and L-aspartate) addition on L-arginine production of ARG were studied, and the addition of L-glutamine and L-aspartate was beneficial for L-arginine production. Then, the glutamine synthetase gene glnA and aspartase gene aspA from E. coli were overexpressed in ARG for increasing the L-glutamine and L-aspartate synthesis, and the L-arginine production was effectively increased. In addition, the L-glutamate supply re-emerged as a limiting factor for L-arginine biosynthesis. Finally, the glutamate dehydrogenase gene gdh was co-overexpressed for further enhancement of L-arginine production. The final strain could produce 53.2 g l^-1 of L-arginine, which was increased by 41.5% compared to ARG in fed-batch fermentation.

Metabolic engineering of Corynebacterium crenatium for enhancing production of higher alcohols

Biosynthesis approaches for the production of higher alcohols as a source of alternative fossil fuels have garnered increasing interest recently. However, there is little information available in the literature about using undirected whole-cell mutagenesis (UWCM) in vivo to improve higher alcohols production. In this study, for the first time, we approached this question from two aspects: first preferentially improving the capacity of expression host, and subsequently optimizing metabolic pathways using multiple genetic mutations to shift metabolic flux toward the biosynthetic pathway of target products to convert intermediate 2-keto acid compounds into diversified C4~C5 higher alcohols using UWCM in vivo, with the aim of improving the production. The results demonstrated the production of higher alcohols including isobutanol, 2-methyl-1-butanol, 3-methyl-1-butanol from glucose and duckweed under simultaneous saccharification and fermentation (SSF) scheme were higher based on the two aspects compared with only the use of wild-type stain as expression host. These findings showed that the improvement via UWCM in vivo in the two aspects for expression host and metabolic flux can facilitate the increase of higher alcohols production before using gene editing technology. Our work demonstrates that a multi-faceted approach for the engineering of novel synthetic pathways in microorganisms for improving biofuel production is feasible.

Improvement of the intracellular environment for enhancing l-arginine production of Corynebacterium glutamicum by inactivation of H2O2-forming flavin reductases and optimization of ATP supply

l-arginine, a semi essential amino acid, is an important amino acid in food flavoring and pharmaceutical industries. Its production by microbial fermentation is gaining more and more attention. In previous work, we obtained a new l-arginine producing Corynebacterium crenatum (subspecies of Corynebacterium glutamicum) through mutation breeding. In this work, we enhanced l-arginine production through improvement of the intracellular environment. First, two NAD(P)H-dependent H₂O₂-forming flavin reductases Frd181 (encoded by frd1 gene) and Frd188 (encoded by frd2) in C. glutamicum were identified for the first time. Next, the roles of Frd181 and Frd188 in C. glutamicum were studied by overexpression and deletion of the encoding genes, and the results showed that the inactivation of Frd181 and Frd188 was beneficial for cell growth and l-arginine production, owing to the decreased H₂O₂ synthesis and intracellular reactive oxygen species (ROS) level, and increased intracellular NADH and ATP levels. Then, the ATP level was further increased by deletion of noxA (encoding NADH oxidase) and amn (encoding AMP nucleosidase), and overexpression of pgk (encoding 3-phosphoglycerate kinase) and pyk (encoding pyruvate kinase), and the l-arginine production and yield from glucose were significantly increased. In fed-batch fermentation, the l-arginine production and yield from glucose of the final strain reached 57.3g/L and 0.326g/g, respectively, which were 49.2% and 34.2% higher than those of the parent strain, respectively. ROS and ATP are important elements of the intracellular environment, and l-arginine biosynthesis requires a large amount of ATP. For the first time, we enhanced l-arginine production and yield from glucose through reducing the H₂O₂ synthesis and increasing the ATP supply.

Systems pathway engineering of Corynebacterium crenatum for improved L-arginine production

L-arginine is an important amino acid in food and pharmaceutical industries. Until now, the main production method of L-arginine in China is the highly polluting keratin acid hydrolysis. The industrial level L-arginine production by microbial fermentation has become an important task. In previous work, we obtained a new L-arginine producing Corynebacterium crenatum (subspecies of Corynebacterium glutamicum) through screening and mutation breeding. In this work, we performed systems pathway engineering of C. crenatum for improved L-arginine production, involving amplification of L-arginine biosynthetic pathway flux by removal of feedback inhibition and overexpression of arginine operon; optimization of NADPH supply by modulation of metabolic flux distribution between glycolysis and pentose phosphate pathway; increasing glucose consumption by strengthening the preexisting glucose transporter and exploitation of new glucose uptake system; channeling excess carbon flux from glycolysis into tricarboxylic acid cycle to alleviate the glucose overflow metabolism; redistribution of carbon flux at α-ketoglutarate metabolic node to channel more flux into L-arginine biosynthetic pathway; minimization of carbon and cofactor loss by attenuation of byproducts formation. The final strain could produce 87.3 g L(-1) L-arginine with yield up to 0.431 g L-arginine g(-1) glucose in fed-batch fermentation.

Effect of Polyhydroxybutyrate (PHB) storage on L-arginine production in recombinant Corynebacterium crenatum using coenzyme regulation

BACKGROUND

Corynebacterium crenatum SYPA 5 is the industrial strain for L-arginine production. Poly-β-hydroxybutyrate (PHB) is a kind of biopolymer stored as bacterial reserve materials for carbon and energy. The introduction of the PHB synthesis pathway into several strains can regulate the global metabolic pathway. In addition, both the pathways of PHB and L-arginine biosynthesis in the cells are NADPH-dependent. NAD kinase could upregulate the NADPH concentration in the bacteria. Thus, it is interesting to investigate how both PHB and NAD kinase affect the L-arginine biosynthesis in C. crenatum SYPA 5.

RESULTS

C. crenatum P1 containing PHB synthesis pathway was constructed and cultivated in batch fermentation for 96 h. The enzyme activities of the key enzymes were enhanced comparing to the control strain C. crenatum SYPA 5. More PHB was found in C. crenatum P1, up to 12.7 % of the dry cell weight. Higher growth level and enhanced glucose consumptions were also observed in C. crenatum P1. With respect to the yield of L-arginine, it was 38.54 ± 0.81 g/L, increasing by 20.6 %, comparing to the control under the influence of PHB accumulation. For more NADPH supply, C. crenatum P2 was constructed with overexpression of NAD kinase based on C. crenatum P1. The NADPH concentration was increased in C. crenatum P2 comparing to the control. PHB content reached 15.7 % and 41.11 ± 1.21 g/L L-arginine was obtained in C. crenatum P2, increased by 28.6 %. The transcription levels of key L-arginine synthesis genes, argB, argC, argD and argJ in recombinant C. crenatum increased 1.9-3.0 times compared with the parent strain.

CONCLUSIONS

Accumulation of PHB by introducing PHB synthesis pathway, together with up-regulation of coenzyme level by overexpressing NAD kinase, enables the recombinant C. crenatum to serve as high-efficiency cell factories in the long-time L-arginine fermentation. Furthermore, batch cultivation of the engineered C. crenatum revealed that it could accumulate both extracellular L-arginine and intracellular PHB simultaneously. All of these have a potential biotechnological application as a strategy for high-yield L-arginine.

Novel technologies provide more engineering strategies for amino acid-producing microorganisms

Traditionally, amino acid-producing strains were obtained by random mutagenesis and subsequent selection. With the development of genetic and metabolic engineering techniques, various microorganisms with high amino acid production yields are now constructed by rational design of targeted biosynthetic pathways. Recently, novel technologies derived from systems and synthetic biology have emerged and open a new promising avenue towards the engineering of amino acid production microorganisms. In this review, these approaches, including rational engineering of rate-limiting enzymes, real-time sensing of end-products, pathway optimization on the chromosome, transcription factor-mediated strain improvement, and metabolic modeling and flux analysis, were summarized with regard to their application in microbial amino acid production.

Controlling the transcription levels of argGH redistributed l-arginine metabolic flux in N-acetylglutamate kinase and ArgR-deregulated Corynebacterium crenatum

Corynebacterium crenatum SYPA5-5, an l-arginine high-producer obtained through multiple mutation-screening steps, had been deregulated by the repression of ArgR that inhibits l-arginine biosynthesis at genetic level. Further study indicated that feedback inhibition of SYPA5-5 N-acetylglutamate kinase (CcNAGK) by l-arginine, as another rate-limiting step, could be deregulated by introducing point mutations. Here, we introduced two of the positive mutations (H268N or R209A) of CcNAGK into the chromosome of SYPA5-5, however, resulting in accumulation of large amounts of the intermediates (l-citrulline and l-ornithine) and decreased production of l-arginine. Genetic and enzymatic levels analysis involved in l-arginine biosynthetic pathway of recombinants SYPA5-5-NAGKH268N (H-7) and SYPA5-5-NAGKR209A (R-8) showed that the transcription levels of argGH decreased accompanied with the reduction of argininosuccinate synthase and argininosuccinase activities, respectively, which led to the metabolic obstacle from l-citrulline to l-arginine. Co-expression of argGH with exogenous plasmid in H-7 and R-8 removed this bottleneck and increased l-arginine productivity remarkably. Compared with SYPA5-5, fermentation period of H-7/pDXW-10-argGH (H-7-GH) reduced to 16 h; meanwhile, the l-arginine productivity improved about 63.6 %. Fed-batch fermentation of H-7-GH in 10 L bioreactor produced 389.9 mM l-arginine with the productivity of 5.42 mM h−1. These results indicated that controlling the transcription of argGH was a key factor for regulating the metabolic flux toward l-arginine biosynthesis after deregulating the repression of ArgR and feedback inhibition of CcNAGK, and therefore functioned as another regulatory mode for l-arginine production. Thus, deregulating all these three regulatory modes was a powerful strategy to construct l-arginine high-producing C. crenatum.

Modular pathway engineering of Corynebacterium glutamicum for production of the glutamate-derived compounds ornithine, proline, putrescine, citrulline, and arginine

The glutamate-derived bioproducts ornithine, citrulline, proline, putrescine, and arginine have applications in the food and feed, cosmetic, pharmaceutical, and chemical industries. Corynebacterium glutamicum is not only an excellent producer of glutamate but also of glutamate-derived products. Here, engineering targets beneficial for ornithine production were identified and the advantage of rationally constructing a platform strain for the production of the amino acids citrulline, proline, and arginine, and the diamine putrescine was demonstrated. Feedback alleviation of N-acetylglutamate kinase, tuning of the promoter of glutamate dehydrogenase gene gdh, lowering expression of phosphoglucoisomerase gene pgi, along with the introduction of a second copy of the arginine biosynthesis operon argCJB(A49V,M54V)D into the chromosome resulted in a C. glutamicum strain producing ornithine with a yield of 0.52 g ornithine per g glucose, an increase of 71% as compared to the parental ΔargFRG strain. Strains capable of producing 0.41 g citrulline per g glucose, 0.29 g proline per g glucose, 0.30 g arginine per g glucose, and 0.17 g putrescine per g glucose were derived from the ornithine-producing platform strain by plasmid-based overexpression of appropriate pathway modules with one to three genes.

Effect of Tween 40 and DtsR1 on L-arginine overproduction in Corynebacterium crenatum

Background

l-Glutamate is an important precursor in the l-arginine (l-Arg) biosynthetic pathway. Various methods, including polyoxyethylene sorbitan monopalmitate (Tween 40) addition and dtsR1 disruption, have been widely used to induce l-glutamate overproduction in Corynebacterium glutamicum. In this study, a novel strategy for l-Arg overproduction through Tween 40 trigger and ΔdtsR1 mutant were proposed in Corynebacterium crenatum.

Results

Corynebacterium crenatum mutant (CCM01) was selected as a host strain, whose argR was lethal via mutagenesis screening, the proB gene was knocked out, and argB was replaced by argB M4 (E19R, H26E, D311R, and D312R) to release l-Arg feedback resistance. After Tween 40 trigger in the logarithmic period, l-Arg production increased from 15.22 to 17.73 g/L in CCM01 strain. When NCgl1221 and dtsR1 disruption (CCM03), l-Arg production drastically increased to 27.45 g/L and then further to 29.97 g/L after Tween 40 trigger. Moreover, the specific activity of α-oxoglutarate dehydrogenase complex (ODHC) decreased, whereas the regeneration of NADP⁺/NADPH significantly increased after dtsR1 disruption and Tween 40 trigger. Results of real-time PCR showed that the transcriptional levels of odhA, sucB, and lpdA (encoding three subunits of the ODHC complex) were downregulated after Tween 40 trigger or dtsR1 disruption. By contrast, zwf transcription (encoding glucose-6-phosphate dehydrogenase) showed no significant difference among CCM01, CCM02 (ΔNCgl1221), and CCM03 (ΔNCgl1221ΔdtsR1) strains without Tween 40 trigger but evidently increased by 5.50 folds after Tween 40 trigger.

Conclusion

A novel strategy for l-Arg overproduction by dtsR1 disruption and Tween 40 trigger in C. crenatum was reported. Tween 40 addition exhibited a bifunctional mechanism for l-Arg overproduction, including reduced ODHC activity and enhanced NADPH pools accumulation by downregulated dtsR1 expression and upregulated zwf expression, respectively.