Efficient biotransformation of l-lysine into cadaverine by strengthening pyridoxal 5’-phosphate-dependent proteins in Escherichia coli with cold shock treatment

Regulating effects of low salt dry-curing pre-treatment on microbiota, biochemical changes and flavour precursors of grass carp (Ctenopharyngodon idella) fillets during storage at 4 °C

Low salt dry-curing (LSD), as a healthier pre-treatment for the preservation of fishery products, is a potential technique substitute for excessively salty curing. The regulatory effects of 2 % and 3 % LSD on the quality evolution through an intrinsic correlation between microbiota succession and flavour precursors of refrigerated grass carp fillets were investigated in this study. The results showed that the LSD pre-treatment was effective in promoting proteolysis, free amino acid and fatty acid metabolism with the microbiota succession and quality evolution. Compared with unpre-treated samples, the 3 % LSD pre-treatment effectively extended the shelf life by 10 days within the acceptable quality attributes. Not only did the LSD pre-treatment lead to catalytic microbiota succession and inhibitive spoilage substance production but it also improved the flavour precursors, which are taste-active amino acids and polyunsaturated fatty acids (PUFAs). Moreover, considerable correlations between quality attributes, taste-active amino acids, PUFAs and microbiota were obtained.

Investigation of enzymatic quality and quantity using pyridoxal 5'-phosphate (PLP) regeneration system as a decoy in Escherichia coli

Pyridoxal 5'-phosphate (PLP), an essential cofactor for multiple enzymes, was used as a protein decoy to prompt enzyme expression and activity for the first time. The best chassis, denoted as WJK, was developed using a pyridoxal kinase (PdxK) and integrated at the HK022 phage attack site of Escherichia coli W3110. When compared with the original strain, the amount and activity of lysine decarboxylase (CadA) in WJK were significantly increased by 100 % and 120 %, respectively. When supplementary nineteen amino acids as second carbon source, cell growth and protein trade-off were observed. The transcriptional levels of genes from glycolysis to TCA cycle, adhE, argH and gdhA were dominating and redirected more flux into α-ketoglutarate, thus facilitated cell growth. Stepwise improvement was conducted with pyridoxal and nitrogen-rich medium; hence, CadA activity was increased to 60 g-cadaverine/g-dry cell weight/h. By reutilizing the whole-cell biocatalysts in two repeated reactions with the supplementation of fresh cells, a total cadaverine of 576 g/L was obtained even without additional PLP. Notably, PLP decoy augment the enzymatic activities of 5-aminolevulinic acid synthase and glutamate/lysine/arginine decarboxylases by over 100 %. Finally, a conserved PLP-binding pocket, Ser-His-Lys, was identified as a vital PLP sponge site that simultaneously improved protein quality and quantity.

A direct enzymatic evaluation platform (DEEP) to fine-tuning pyridoxal 5'-phosphate-dependent proteins for cadaverine production

Pyridoxal 5'-phosphate (pyridoxal phosphate, PLP) is an essential cofactor for multiple enzymatic reactions in industry. However, cofactor engineering based on PLP regeneration and related to the performance of enzymes in chemical production has rarely been discussed. First, we found that MG1655 strain was sensitive to nitrogen source and relied on different amino acids, thus the biomass was significantly reduced when PLP excess in the medium. Then, the six KEIO collection strains were applied to find out the prominent gene in deoxyxylulose-5-phosphate (DXP) pathway, where pdxB was superior in controlling cell growth. Therefore, the clustered regularly interspaced short palindromic repeats interference (CRISPRi) targeted on pdxB in MG1655 was employed to establish a novel direct enzymatic evaluation platform (DEEP) as a high-throughput tool and obtained the optimal modules for incorporating of PLP to enhance the biomass and activity of PLP-dependent enzymes simultaneously. As a result, the biomass has increased by 55% using P_lacI promoter driven pyridoxine 5'-phosphate oxidase (PdxH) with a trace amount of precursor. When the strains incorporated DEEP and lysine decarboxylase (CadA), the cadaverine productivity was increased 32% due to the higher expression of CadA. DEEP is not only feasible for high-throughput screening of the best chassis for PLP engineering but also practical in fine-tuning the quantity and quality of enzymes.

High-efficiency production of 5-hydroxyectoine using metabolically engineered Corynebacterium glutamicum

BACKGROUND

Extremolytes enable microbes to withstand even the most extreme conditions in nature. Due to their unique protective properties, the small organic molecules, more and more, become high-value active ingredients for the cosmetics and the pharmaceutical industries. While ectoine, the industrial extremolyte flagship, has been successfully commercialized before, an economically viable route to its highly interesting derivative 5-hydroxyectoine (hydroxyectoine) is not existing.

RESULTS

Here, we demonstrate high-level hydroxyectoine production, using metabolically engineered strains of C. glutamicum that express a codon-optimized, heterologous ectD gene, encoding for ectoine hydroxylase, to convert supplemented ectoine in the presence of sucrose as growth substrate into the desired derivative. Fourteen out of sixteen codon-optimized ectD variants from phylogenetically diverse bacterial and archaeal donors enabled hydroxyectoine production, showing the strategy to work almost regardless of the origin of the gene. The genes from Pseudomonas stutzeri (PST) and Mycobacterium smegmatis (MSM) worked best and enabled hydroxyectoine production up to 97% yield. Metabolic analyses revealed high enrichment of the ectoines inside the cells, which, inter alia, reduced the synthesis of other compatible solutes, including proline and trehalose. After further optimization, C. glutamicum Ptuf ectD^PST achieved a titre of 74 g L^-1 hydroxyectoine at 70% selectivity within 12 h, using a simple batch process. In a two-step procedure, hydroxyectoine production from ectoine, previously synthesized fermentatively with C. glutamicum ectABC^opt, was successfully achieved without intermediate purification.

CONCLUSIONS

C. glutamicum is a well-known and industrially proven host, allowing the synthesis of commercial products with granted GRAS status, a great benefit for a safe production of hydroxyectoine as active ingredient for cosmetic and pharmaceutical applications. Because ectoine is already available at commercial scale, its use as precursor appears straightforward. In the future, two-step processes might provide hydroxyectoine de novo from sugar.

Catalytic Production of Functional Monomers from Lysine and Their Application in High-Valued Polymers

Lysine is a key raw material in the chemical industry owing to its sustainability, mature fermentation process and unique chemical structure, besides being an important nutritional supplement. Multiple commodities can be produced from lysine, which thus inspired various catalytic strategies for the production of these lysine-based chemicals and their downstream applications in functional polymer production. In this review, we present a fundamental and comprehensive study on the catalytic production process of several important lysine-based chemicals and their application in highly valued polymers. Specifically, we first focus on the synthesis process and some of the current industrial production methods of lysine-based chemicals, including ε-caprolactam, α-amino-ε-caprolactam and its derivatives, cadaverine, lysinol and pipecolic acid. Second, the applications and prospects of these lysine-based monomers in functional polymers are discussed such as derived poly (lysine), nylon-56, nylon-6 and its derivatives, which are all of growing interest in pharmaceuticals, human health, textile processes, fire control and electronic manufacturing. We finally conclude with the prospects of the development of both the design and synthesis of new lysine derivatives and the expansion of the as-synthesized lysine-based monomers in potential fields.

Production of γ-Aminobutyrate (GABA) in Recombinant Corynebacterium glutamicum by Expression of Glutamate Decarboxylase Active at Neutral pH

γ-Aminobutyrate (GABA) is an important chemical by itself and can be further used for the production of monomer used for the synthesis of biodegradable polyamides. Until now, GABA production usingCorynebacterium glutamicum harboring glutamate decarboxylases (GADs) has been limited due to the discrepancy between optimal pH for GAD activity (pH 4.0) and cell growth (pH 7.0). In this study, we developed recombinant C. glutamicum strains expressing mutated GAD from Escherichia coli (EcGADmut) and GADs from Lactococcus lactis CICC20209 (LlGAD) and Lactobacillus senmaizukei (LsGAD), all of which showed enhanced pH stability and adaptability at a pH of approximately 7.0. In shake flask cultivations, the GABA productions of C. glutamicum H36EcGADmut, C. glutamicum H36LsGAD, and C. glutamicum H36LlGAD were examined at pH 5.0, 6.0, and 7.0, respectively. Finally, C. glutamicum H36EcGADmut (40.3 and 39.3 g L^-1), H36LlGAD (42.5 and 41.1 g L^-1), and H36LsGAD (41.6 and 40.2 g L^-1) produced improved GABA titers and yields in batch fermentation at pH 6.0 and pH 7.0, respectively, from 100 g L^-1 glucose. The recombinant strains developed in this study could be used for the establishment of sustainable direct fermentative GABA production from renewable resources under mild culture conditions, thus increasing the availability of various GADs.

Purification and biofabrication of 5-aminolevulinic acid for photodynamic therapy against pathogens and cancer cells

5-Aminolevulinic acid (5-ALA) is a non-proteinogenic amino acid which has involved in heme metabolism of organisms, and has been widely applied in agriculture, and medical fields nowadays. 5-ALA is used in the elimination of pathogens or cancer cells by photodynamic therapy (PDT) owing to the photosensitizer reaction which releases the reactive oxygen species (ROS). Currently, biofabrication of 5-ALA is regarded as the most efficient and eco-friendly approach, but the complicated ingredient of medium causes the nuisance process of purification, resulting in low recovery and high producing cost. In this study, hydrogen chloride, sodium acetate, and ammonia were examined to maximize the recovery of 5-ALA from ion-exchange chromatography (IEC), thus a 92% recovery in 1 M ammonia at pH 9.5 was obtained. Afterward, the activated carbon was used for decolorization to further remove the pigments from the eluent. Four organic solvents, i.e., diethyl ether, methanol, ethanol, and acetone were compared to extract and form 5-ALA precipitation. The purified 5-ALA was verified to eliminate 74% of A549 human lung cancer and 83% of A375 melanoma skin cancer cell. Moreover, Proteus hauseri, Aeromonas hydrophila, Bacillus cereus, and Staphylococcus aureus were killed via anti-microbial PDT with 1% 5-ALA and reached 100% killing rate at optimal condition. With the addition of 0.05% 5-ALA during the culture, the growth of microalgae Chlorella sorokiniana was improved to against a common aquatic pathogen, A. hydrophila. The broad application of 5-ALA was demonstrated in this study for the first time.

Engineered Halomonas spp. for production of l-Lysine and cadaverine

Cadaverine, a derivative of l-lysine, has been used as a monomer for the synthesis of bio-based nylon-5,6. This study engineered Halomonas bluephagenesis TD1.0 by blocking the feedback inhibition, overexpressing the key l-lysine synthesis genes, strengthening the l-lysine export system and increasing the supply of oxaloacetate for production of l-lysine in the supernatant and PHB in the cells. Subsequently, cadaverine biosynthetic pathway was constructed in H. campaniensis LC-9 to improve the efficiency of de novo cadaverine biosynthesis which combines l-lysine producing H. bluephagenesis TDL8-68-259 and cadaverine producing H. campaniensis LC-9-ldcC-lysP. When H. campaniensis LC-9-ldcC-lysP was used as a whole cell catalysis for cadaverine production, the conversion efficiency of l-lysine to cadaverine reached 100% in the presence of 0.05% Triton X-100 for cell membrane permeability enhancement, resulting in 118 g L^-1 cadaverine formed in the fermentor. Thus, Halomonas spp. have been successfully constructed for l-lysine and cadaverine production.

Migration of glutamate decarboxylase by cold treatment on whole-cell biocatalyst triggered activity for 4-aminobutyric acid production in engineering Escherichia coli

Glutamate decarboxylase B (GadB) from Escherichia coli, an intrinsic pyridoxal 5'-phosphate (PLP)-dependent enzyme has been employed for 4-aminobutyric acid (GABA) biosynthesis, which involves the glutamate import and GABA export via a transporter located in the inner membrane as rate determined step of whole-cell (WC) biotransformation. Herein, GadB was cloned and overexpressed in E. coli under a constitutive promoter in a high copy number plasmid, and 46.9 g/L GABA was produced. It was observed that GadB migrated to the periplasm when the WC were subjected to -20 °C cold treatment for 24 h prior to the biotransformation. Kinetic studies indicated that the enzymatic turnover rate of WC increased 2-fold after cold treatment, which was correlated with the migration rate of GadB, and up to 88.6% of GadB. The export or possible migration of GadB mitigated the rate-limiting step of WC biotransformation, and a 100% conversion of substrate to GABA was obtained. Finally, we launched a promising strategy for GABA production of 850 g/L from cost-effective monosodium glutamate (MSG) by using WC biocatalysts with 10-times recycling.

Green chemical and biological synthesis of cadaverine: recent development and challenges

Cadaverine has great potential to be used as an important monomer for the development of a series of high value-added products with market prospects. The most promising strategies for cadaverine synthesis involve using green chemical and bioconversion technologies. Herein, the review focuses on the progress and strategies towards the green chemical synthesis and biosynthesis of cadaverine. Specifically, we address the specific biosynthetic pathways of cadaverine from different substrates as well as extensively discussing the origination, structure and catalytic mechanism of the key lysine decarboxylases. The advanced strategies for process intensification, the separation and purification of cadaverine have been summarized. Furthermore, the challenging issues of the environmental, economic, and applicable impact for cadaverine production are also highlighted. This review concludes with the promising outlooks of state-of-the-art applications of cadaverine along with some insights toward their challenges and potential improvements.

Progress and strategies towards the green chemo/bio-synthesis of cadaverine with special attention to their environmental, economic, and applicable impact are reviewed.

Whole-cell biocatalyst for cadaverine production using stable, constitutive and high expression of lysine decarboxylase in recombinant Escherichia coli W3110

Microbial production of industrial chemicals is a sustainable approach to reduce the dependence on petroleum-based chemicals such as acids, alcohols, and amines, in which the cadaverine is a natural diamide and serves as one of the key monomers for biopolymer production. In this study, the constitutive promoter J23100 driven lysine decarboxylase (CadA) for cadaverine production was established and compared in different Escherichia coli strains. The best chassis designed as JW, expressed the highest amount of CadA by using J23100 promoter, showing stable and high copy numbers (i.e., PCN > 100) when culture in the antibiotic-free medium. JW attained a CadA activity of 167 g-DAP/g-DCW-h and had the maximum biocatalyst of 45.6 g-DCW/L in fed-batch fermentation. In addition, JW was able to convert 2.5 M L-lysine to 221 g/L cadaverine, with 86 % yield and 55.3 g/L-h productivity. The whole-cell biocatalyst could be reused over four times at an average of 97 % conversion when supplied half of fresh cells in the reaction. This work developed a stable, constitutive expression, long-term preservation, high-level expression of CadA for DAP production, and paved an alternative opportunity of bio-nylon for industry in the future.

Plasmid-Free System and Modular Design for Efficient 5-Aminolevulinic Acid Production by Engineered Escherichia coli

5-Aminolevulinic acid (ALA) is an essential intermediate for many organisms and has been considered for the applications of medical especially in photodynamic therapy of cancer recently. However, ALA production via chemical approach is complicated; hence, microbial manufacturing has received more attentions. In this study, a modular design to simultaneously express ALA synthase from Rhodobacter sphaeroides (RshemA), a non-specific ALA exporter (RhtA), and chaperones was first developed and discussed. The ALA production was significantly increased by coexpressing RhtA and RshemA. Besides, ALA was enhanced by the cofactor pyridoxal phosphate (PLP) which was supplied by expressing genes of pdxK and pdxY or direct addition. However, inclusion bodies of RshemA served as an obstacle; thus, chaperones DnaK and GroELS were introduced to reform the conformation of proteins and successfully improved ALA production. Finally, a plasmid-free strain RrGI, as the robust chassis, was established and a 6.23-fold enhancement on ALA biosynthesis and led to 7.47 g/L titer and 0.588 g/L/h productivity under the optimal cultural condition.

Fabrication of bio-based polyamide 56 and antibacterial nanofiber membrane from cadaverine

A green bioprocess for the fabrication of nanofiber membranes from the biomaterial polyamide 56 (PA56) via electrospinning was proposed. Cadaverine, as the precursor of PA56, was first produced from recombinant Escherichia coli using the whole-cell biotransformation of lysine. PA56 was then fabricated by mixing adipic acid with purified cadaverine obtained from solvent extraction and distillation. The thermal properties of the fabricated PA56 are as follows: a melting point of 250 °C, a crystallization point of 220 °C, and a degradation temperature of 410 °C. A PA56 nanofiber membrane (PAM) was further prepared via electrospinning. Dyed membranes (P-Dye) were obtained by the reaction of Reactive Red 141 dye with the amino group of PAM. Poly-(hexamethylene biguanide) (PHMB) was attached to the P-Dye to create P-Dye-PHMB. On the other hand, PAM with alginate, used to facilitate PHMB attachment (P-Alg-PHMB), was compared with P-Dye-PHMB in terms of antibacterial activity against pathogenic strains of E. coli and Pseudomonas putida. P-Alg-PHMB showed excellent antibacterial efficiency for E. coli (97%) and P. putida (100%). The proposed bioprocess can be used to fabricate novel membranes for biomedical applications and functional textiles.

Redirection of metabolic flux in Shewanella oneidensis MR-1 by CRISPRi and modular design for 5-aminolevulinic acid production

Programming non-canonical organisms is more attractive due to the prospect of high-value chemical production. Among all, Shewanella oneidensis MR-1 possesses outstanding heme synthesis ability and is well-known for electron transfer, thus has high potential in microbial fuel cell and bioremediation. However, heme, as the final product of C4 and C5 pathways, is regulated by heme cluster for the high-value 5-aminolevulinic acid (ALA) for cancer photodynamic therapy, which has never been explored in MR-1. Herein, the heme metabolism in MR-1 was firstly optimized for ALA production. We applied CRISPR interference (CRISPRi) targeted on the genes to fine-tune carbon flux in TCA cycle and redirected the carbon out-flux from heme, leading to a significant change in the amino acid profiles, while downregulation of the essential hemB showed a 2-fold increasing ALA production via the C5 pathway. In contrast, the modular design including of glucokinase, GroELS chaperone, and ALA synthase from Rhodobacter capsulatus enhanced ALA production markedly in the C4 pathway. By integrating gene cluster under dual T7 promoters, we obtained a new strain M::TRG, which significantly improved ALA production by 145-fold. We rewired the metabolic flux of MR-1 through this modular design and successfully produced the high-value ALA compound at the first time.

Pyridoxal kinase PdxY mediated carbon dioxide assimilation to enhance the biomass in Chlamydomonas reinhardtii CC-400

Microalga served as the promising bioresources due to the high efficiency of carbon dioxide conversion. However, the application of microalga is still restricted by low biomass, easier contamination, and high cost of production. To overcome the challenge, engineered Chlamydomonas reinhardtii CC-400 with pyridoxal kinase gene (pdxY) has demonstrated in this study. The results indicated CC-400 with pdxY reached enhanced algal biomass in three different systems, including flask, Two-layer Photo-Reactor (TPR) and airlift Photo-Bioreactor (PBR). The genetic strain PY9 cultured with 1% CO₂ in the PBR showed a significant enhancement of biomass up to 1.442 g/L, a 2-times of that of the wild type. We also found the transcriptional levels of carbonic anhydrase (CA) dropped down in PY9 while higher levels of RuBisCo and pdxY occurred, thus the carbon dioxide assimilation under mixotrophic culture dramatically increased. We proofed that pdxY successfully mediated carbon dioxide utilization in CC-400.

Improvement of cadaverine production in whole cell system with baker's yeast for cofactor regeneration

Cadaverine, 1,5-diaminopentane, is one of the most promising chemicals for biobased-polyamide production and it has been successfully produced up to molar concentration. Pyridoxal 5'-phosphate (PLP) is a critical cofactor for inducible lysine decarboxylase (CadA) and is required up to micromolar concentration level. Previously the regeneration of PLP in cadaverine bioconversion has been studied and salvage pathway pyridoxal kinase (PdxY) was successfully introduced; however, this system also required a continuous supply of adenosine 5'-triphosphate (ATP) for PLP regeneration from pyridoxal (PL) which add in cost. Herein, to improve the process further a method of ATP regeneration was established by applying baker's yeast with jhAY strain harboring CadA and PdxY, and demonstrated that providing a moderate amount of adenosine 5'-triphosphate (ATP) with the simple addition of baker's yeast could increase cadaverine production dramatically. After optimization of reaction conditions, such as PL, adenosine 5'-diphosphate, MgCl₂, and phosphate buffer, we able to achieve high production (1740 mM, 87% yield) from 2 M L-lysine. Moreover, this approach could give averaged 80.4% of cadaverine yield after three times reactions with baker's yeast and jhAY strain. It is expected that baker's yeast could be applied to other reactions requiring an ATP regeneration system.

Development of chromosome-based T7 RNA polymerase and orthogonal T7 promoter circuit in Escherichia coli W3110 as a cell factory

Background

Orthogonal T7 RNA polymerase (T7RNAP) and T7 promoter is a powerful genetic element to mediate protein expression in different cells. Among all, Escherichia coli possess advantages of fast growth rate, easy for culture and comprehensive elements for genetic engineering. As E. coli W3110 owns the benefits of more heat shock proteins and higher tolerance to toxic chemicals, further execution of T7-based system in W3110 as cell factory is a conceivable strategy.

Results

Three novel W3110 strains, i.e., W3110:IL5, W3110::L5 and W3110::pI, were accomplished by chromosome-equipped T7RNAP. At first, the LacZ and T7RNAP with isopropyl-β-D-thiogalactopyranoside (IPTG) induction showed higher expression levels in W3110 derivatives than that in BL21(DE3). The plasmids with and without lacI/lacO repression were used to investigate the protein expression of super-fold green fluorescence protein (sfGFP), carbonic anhydrase (CA) for carbon dioxide uptake and lysine decarboxylase (CadA) to produce a toxic chemical cadaverine (DAP). All the proteins showed better expression in W3110::L5 and W3110::pI, respectively. As a result, the highest cadaverine production of 36.9 g/L, lysine consumption of 43.8 g/L and up to 100% yield were obtained in W3110::pI(−) with plasmid pSU-T7-CadA constitutively.

Conclusion

Effect of IPTG and lacI/lacO regulator has been investigated in three chromosome-based T7RNAP E. coli strains. The newly engineered W3110 strains possessed similar protein expression compared to commercial BL21(DE3). Furthermore, W3110::pI displays higher production of sfGFP, CA and CadA, due to it having the highest sensitivity to IPTG, thus it represents the greatest potential as a cell factory.