Cadaverine and putrescine exposure influence carbon and nitrogen cycling genes in water and sediment of the Yellow River

The response patterns of microbial functional genes involved in biogeochemical cycles to cadaver decay is a central topic of recent environmental sciences. However, the response mechanisms and pathways of the functional genes associated with the carbon (C) and nitrogen (N) cycling to cadaveric substances such as cadaverine and putrescine remain unclear. This study explored the variation of functional genes associated with C fixation, C degradation and N cycling and their influencing factors under cadaverine, putrescine and mixed treatments. Our results showed only putrescine significantly increased the alpha diversity of C fixation genes, while reducing the alpha diversity of N cycling genes in sediment. For the C cycling, the mixed treatment significantly decreased the total abundance of reductive acetyl-CoA pathway genes (i.e., acsB and acsE) and lig gene linked to lignin degradation in water, while only significantly increasing the hydroxypropionate-hydroxybutylate cycle (i.e., accA) gene abundance in sediment. For the N cycling, mixed treatment significantly decreased the abundance of the nitrification (i.e., amoB), denitrification (i.e., nirS3) genes in water and the assimilation pathway gene (i.e., gdhA) in sediment. Environmental factors (i.e., total carbon and total nitrogen) were all negatively associated with the genes of C and N cycling. Therefore, cadaverine and putrescine exposure may inhibit the pathway in C fixation and N cycling, while promoting C degradation. These findings can offer some new insight for the management of amine pollution caused by animal cadavers.

Reduction of histamine, putrescine and cadaverine by the bacteria Lacticaseibacillus casei depending on selected factors in the real condition of the dairy product

One way to effectively reduce the number of biogenic amines (BAs) in food is through enzymatic reduction using bacteria, such as lactic acid bacteria. This study focuses on the ability of the bacterial strain Lacticaseibacillus casei CCDM 198 to reduce the number of three important BAs (histamine, putrescine and cadaverine) over time, depending on different conditions (temperature and pH) in vitro and for the real dairy product - skimmed milk. The obtained results show that the studied strain significantly (P < 0.05) affects the number of individual amines, and the content of all amines has a decreasing character compared to the initial relative content of BAs at time zero. Furthermore, a statistical dependence (P < 0.05) of the rate of amine degradation on the combination of investigated factors was demonstrated. The presence and the activity of multicopper oxidase enzyme was also detected in this bacterial strain. This is the first known publication demonstrating multicopper oxidase activity in Lacticaseibacillus casei CCDM 198. Moreover, the studied strain is able to reduce the tested BAs in skimmed milk and would be a good candidate for degrading these toxic compounds in other dairy products, such as cheese. These findings could significantly enhance the food safety of dairy products.

Evaluation of the ecotoxicological effects of biogenic amines derived from cadaverous putrefaction on springtails Folsomia candida

Necro-leachate, a liquid released during cadaveric decomposition, is considered the main culprit for impacts on cemetery environments. The biogenic amines cadaverine and putrescine make up part of the composition of necro-leachate and have a certain toxicity to different organisms. Springtails are among the most used bioindicators to assess the impacts of soil contaminants. As there are no data on the acute and chronic toxicity of springtails exposed to cadaverine and putrescine, the objective of this study was to evaluate the toxic potential of both amines, under the behavioral effect of avoidance and reproduction in the species Folsomia candida. Springtails were exposed to soils contaminated with different concentrations of cadaverine and putrescine, and different mixtures of these amines. To evaluate the avoidance and reproduction test, the individuals were exposed for periods of 48 h and 28 days, respectively. The results obtained in the avoidance test showed that springtails exhibited a preference for the treated soil in both isolated and mixed treatments. The chronic evaluation assays showed that the reproduction was affected, particularly in the treatments with combined amines, resulting in a reduction in the total number of juveniles. From the results, it is possible to infer that the methods applied in this research have provided information that will contribute to a better understanding of the toxicity of putrefactive biogenic amines, since there exist few ecotoxicological studies carried out with these amines, and especially with those from cemetery environments.

A colorimetric and fluorescent sensor for non-destructive screening of the freshness of shrimp and fish

The freshness of fish and shrimp is closely associated with food safety, hence it is a wide concern to develop a facile and effective method for fast, non-destructive and visual screening the freshness of fish and shrimp. Herein, we developed a chromogenic and fluorogenic sensor (RFCC) based on resorufin for sensing of biogenic amines including cadaverine and putrescine. RFCC underwent aminolysis with cadaverine or putrescine, displaying a remarkable fluorescence turn on response at 593 nm along with obvious color change from colorless to pink. RFCC was fabricated into test strips to sense cadaverine vapor, and the RGB value of test strips showed a good linear relationship with the concentration of cadaverine (0.5 - 8.2 × 10³ ppm). The RFCC tag was used to in situ screen the freshness of fish and shrimp according to obvious fluorescence change, and satisfactory results were achieved. Furthermore, this test strip was validated by total volatile base nitrogen (TVBN), providing a simple, low cost and portable tool to screen the freshness of fish and shrimp for consumers and suppliers without expensive instrumentation.

Combination of SPE and fluorescent detection of AQC-derivatives for the determination at sub-mg/L levels of biogenic amines in dairy products

Biogenic amines (BAs) are compounds generated by decarboxylation of their amino acid precursors. Their intake, even at low concentrations, can lead to several types of health problems in sensitive individuals. As they can be easily formed in fermented dairy products, their quantitative determination is very relevant. In the present paper, a method for the quantitative determination of four biogenic amines in different dairy products has been developed, validated and applied to 37 samples of milk, 23 of yogurt, and 14 of kefir. Amines were selectively extracted using solid phase extraction, subsequently derivatizatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate and further determined by High Performance Liquid Chromatography with fluorescence detection. The method's sensitivity was highly satisfactory, with limits of detection lower than 0.2 mg/L. Optimal linearity and repeatability were also achieved. BAs were not detected in most of the milk samples, but they were found frequently at high levels in yogurt and kefir samples, reaching values of up to 79 mg/kg total BAs in kefir samples. Levels measured should not be a cause for concern for the population at large, but should be known by BAs-sensitive individuals.

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.

Multi-omics methods reveal that putrescine and cadaverine cause different degrees of enrichment of high-risk resistomes and opportunistic pathogens in the water and sediment of the Yellow River

Contamination of antibiotic resistomes due to animal carcass decay has become a serious environmental concern. However, the relationship between main metabolite compounds of corpse decomposition (i.e., putrescine and cadaverine) and antibiotic resistomes remains unclear. To tackle this issue, the response of antibiotic resistance genes (ARGs) and microbiome in aquatic environment to excess putrescine, cadaverine and a mixture of both based on laboratory simulation experiment was investigated by high-throughput quantitative PCR and amplicon sequencing methods. Our results showed putrescine and cadaverine led to the increasing of TC (total carbon) and TN (total nitrogen) both in water and sediment. Under the exposure of putrescine and cadaverine, the total abundance of mobile genetic elements (MGEs) and most ARGs in water was higher than in sediment. In particular, putrescine and cadaverine caused significantly different decreases in alpha diversity of microbial community in water and sediment compared with the control group. Microbial community structures both in water and sediment were also significantly affected by cadaverine and putrescine. Furthermore, putrescine and cadaverine led to different degrees of increases of high-risk ARGs (like mecA) and opportunistic pathogens (like Delftia) in sediment, promoting the prevalence of antibiotic resistant bacteria. In conclusion, our findings revealed the influences of main metabolites of carcass decay on microbiome and resistomes, providing references for risk assessment and pollution management.

Simultaneous carbon dioxide sequestration and utilization for cadaverine production using dual promoters in engineered Escherichia coli strains

Human carbonic anhydrase II (hCAII) is a rapid-acting zinc-metalloenzyme that catalyzes CO₂ hydration reversibly, with encouraging applications in carbon capture, sequestration, and utilization (CCSU). However, biocatalyst durability is a major challenge. Herein, hCAII is emphasized in 4 different Escherichia coli strains and designated under dual promoters from sigma factor 70 (σ⁷⁰) and heat shock protein (HSP70A) to suppress the usage of inducer and stimulate activity in heat environments. As a result, hCAII under high-efficient dual promoters regulation retained high residual activity in CO₂ biomineralization of 68.8 % after 4 cycles at 40 °C. Moreover, co-expression of CA_C9 with lysine decarboxylase (CadA) simultaneously sequestered CO₂ release up to 95.7 % and increased cadaverine titer from 18.0 to 36.7 g/L by using E. coli MG1655. The remnant biomass from cadaverine synthesis sustained converting CO₂ to 57.9 mg-CaCO₃. Thus, the dual promoters design demonstrated the promising potential for CCSU through simultaneous CO₂ utilization and cadaverine synthesis.

Enhanced recombinant carbonic anhydrase in T7RNAP-equipped Escherichia coli W3110 for carbon capture storage and utilization (CCSU)

Sulfurihydrogenibium yellowstonense carbonic anhydrase (SyCA) is a well-known thermophilic CA for carbon mineralization. To broaden the applications of SyCA, the activity of SyCA was improved through stepwise engineering and in different cultural conditions, as well as extended to co-expression with other enzymes. The engineered W3110 strains with 4 different T7 RNA polymerase levels were employed for SyCA production. As a result, the best strain WT7L cultured in modified M9 medium with temperature shifted from 37 to 30 °C after induction increased SyCA activity to 9122 U/mL. The SyCA whole-cell biocatalyst was successfully applied for carbon capture and storage (CCS) of CaCO₃. Furthermore, SyCA was applied for low-carbon footprint synthesis of 5-aminolevulinic acid (5-ALA) and cadaverine (DAP) by coupling with ALA synthetase (ALAS) and lysine decarboxylase (CadA), suppressing CO₂ release to -6.1 g-CO₂/g-ALA and -2.53 g-CO₂/g-DAP, respectively. Harnessing a highly active SyCA offers a complete strategy for CCSU in a green process.

Engineering synthetic microbial consortium for cadaverine biosynthesis from glycerol

OBJECTIVES

1,5-pentanediamine (cadaverine) is a C5 platform chemical, also an important raw material for bio-polyamide PA5X. With increasing concerns about the depletion of fossil resources and global environmental protection, cadaverine bio-production has attracted more attentions.

RESULTS

Here, a microbial consortium consisting of Corynebacterium glutamicum cgl-FDK and Escherichia coli BL-ABST-Spy was constructed to de novo synthesize cadaverine utilizing glycerol as the sole carbon resource. The glycerol utilization pathway was initially constructed in C. glutamicum cgl-FDK to produce lysine from glycerol. Then, the pyridoxal 5'-phosphate (PLP) biosynthesis pathway and SpyTag/SpyCatcher protein-ligation system for lysine decarboxylase (CadA) and cadaverine-lysine antiporter protein (CadB) were introduced into E. coli BL-ABST-Spy to synthesize cadaverine from lysine. Furthermore, the fermentation conditions of microbial consortium were optimized and the cadaverine production reached 9.3 g/L with glycerol as the sole carbon source.

CONCLUSIONS

This work provides a promising strategy for efficiently producing cadaverine from glycerol with an artificial microbial consortium.

ATP is not essential for cadaverine production by Escherichia coli whole-cell bioconversion

ATP plays an essential role in the substrate/product transmembrane transportation during whole-cell bioconversion. This study aimed to address the impact of ATP upon cadaverine synthesis by whole-cell biocatalysts. The results showed no significant change in the ATP content (P = 0.625), and the specific cadaverine yield (P = 0.374) was observed in enzyme-catalyzed cadaverine synthesis with exogenous addition of ATP, indicating that the enzyme-catalyzed process does not require the participation of ATP. Furthermore, a whole-cell biocatalyst co-overexpressed methionine adenosyltransferase (MetK), lysine decarboxylase (CadA), and lysine/cadaverine antiporter (CadB) was constructed and used to investigate the effect of ATP deficiency on the cadaverine production by conversion of L-methionine and L-lysine, simultaneously. The results showed no significant difference (P = 0.585) in the specific cadaverine content between high and low levels of intracellular ATP. In addition, the intra- and extracellular cadaverine concentration and the ratio of ATP/ADP of whole-cell biocatalyst were determined. Results showed that the extracellular cadaverine concentration was much higher than the intracellular concentration, and no significant changes in ATP/ADP ratio during cadaverine synthesis. In contrast, an inhibition effect of the proton motive force (PMF) inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) on cadaverine production was detected. These findings strongly suggest that cadaverine transport in whole-cell biocatalysts was energized by PMF rather than ATP. Finally, a model was proposed to describe cadaverine's PMF-driven transport under different external pHs during whole-cell biocatalysis. This study is the first to experimentally confirm that the cadaverine production by Escherichia coli whole-cell bioconversion is independent of intracellular ATP, which helps guide the subsequent construction of biocatalysts and optimize transformation conditions.

Application of Cadaverine to Inhibit Biotin Biosynthesis in Plants

Biotin is an essential vitamin in plants. However, characterization of biotin deficiency has been limited by embryo lethality in mutants, which can only be rescued by supplementation of biotin. Here, we describe a protocol to characterize biotin deficiency in Arabidopsis thaliana through application of the polyamine cadaverine. Cadaverine induces changes in primary root growth. Protein biotinylation in Arabidopsis seedlings can be quantified through an assay similar to a western blot, in which protein biotinylation is detected by a streptavidin probe. This technique provides a chemical means of inhibiting biotin synthesis, allowing for further characterization of biotin deficiency on a physiological and molecular level.

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.

Enhanced thermal and alkaline stability of L-lysine decarboxylase CadA by combining directed evolution and computation-guided virtual screening

As an important monomer for bio-based nylons PA5X, cadaverine is mainly produced by enzymatic decarboxylation of L-lysine. A key issue with this process is the instability of L-lysine decarboxylase (CadA) during the reaction due to the dissociation of CadA subunits with the accumulation of alkaline cadaverine. In this work, we attempted to improve the thermal and alkaline stability of CadA by combining directed evolution and computation-guided virtual screening. Interestingly, site 477 residue located at the protein surface and not the decamer interface was found as a hotspot in directed evolution. By combinatorial mutagenesis of the positive mutations obtained by directed evolution and virtual screening with the previously reported T88S mutation, K477R/E445Q/T88S/F102V was generated as the best mutant, delivering 37% improvement of cadaverine yield at 50 ºC and pH 8.0. Molecular dynamics simulations suggested the improved rigidity of regional structures, increased number of salt bridges, and enhancement of hydrogen bonds at the multimeric interface as possible origins of the improved stability of the mutant. Using this four-point mutant, 160.7 g/L of cadaverine was produced from 2.0 M Lysine hydrochloride at 50 °C without pH regulation, with a conversion of 78.5%, whereas the wild type produced 143.7 g/L cadaverine, corresponding to 70% conversion. This work shows the combination of directed evolution and virtual screening as an efficient protein engineering strategy.

Another casualty of the SARS-CoV-2 pandemic-the environmental impact

Cemetery leachate generated by the process of cadaveric decomposition is a significant contaminant of several matrices in the cemetery environment (soil, groundwater, and surface water). The biogenic amines cadaverine and putrescine stand out among the cemetery leachate contaminants, since they are potentially carcinogenic compounds. This review article presents a discussion of possible environmental impacts caused by the increase in deaths resulting from COVID-19 as its central theme. The study also aims to demonstrate the importance of considering, in this context, some climatic factors that can alter both the time of bodily decomposition and the longevity of the virus in the environment. Additionally, some evidence for the transmission of the virus to health professionals and family members after the patient's death and environmental contamination after the burial of the bodies will also be presented. Several sources were consulted, such as scientific electronic databases (NCBI), publications by government agencies (e.g., ARPEN, Brazil) and internationally recognized health and environmental agencies (e.g., WHO, OurWorldInData.org), as well as information published on reliable websites available for free (e.g., CNN) and scientific journals related to the topic. The data from this study sounds the alarm on the fact that an increase in the number of deaths from the complications of COVID-19 has generated serious environmental problems, resulting from Cemetery leachate.

In-situ food spoilage monitoring using a wireless chemical receptor-conjugated graphene electronic nose

Monitoring food spoilage is one of the most effective methods for preventing food poisoning caused by biogenic amines or microbes. Therefore, various analytical techniques have been introduced to detect low concentrations of cadaverine (CV) and putrescine (PT), which are representative biogenic polyamines involved in food spoilage (5-8 ppm at the stage of initial decomposition after storage for 5 days at 5 °C and 17-186 ppm at the stage of advanced decomposition after storage for 7 days at 5 °C). Although previous methods showed selective CV and PT detection even at low concentrations, the use of these methods remains challenging in research areas that require in-situ, real-time, on-site monitoring. In this study, we demonstrated for the first time an in-situ high-performance chemical receptor-conjugated graphene electronic nose (CRGE-nose) whose limits of detection (LODs), 27.04 and 7.29 ppb, for CV and PT are up to 10² times more sensitive than those of conventional biogenic amine sensors. Specifically, the novel chemical receptors 2,7-bis(3-morpholinopropyl)benzo[lmn][3,8] phenanthroline-1,3,6,8(2H,7H)-tetraone (NaPhdiMor (NPM)) and 2,7-bis(2-((3-morpholinopropyl)amino)ethyl)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NaPhdiEtAmMor (NPEAM)) were designed on the basis of density functional theory (DFT) calculations, and their interaction mechanism was characterized by a DFT 3D simulation. Interestingly, the CRGE-nose was connected on a micro sim chip substrate via wire bonding and then integrated into wireless portable devices, resulting in a cost-effective, high-performance prototype CRGE-nose device capable of on-site detection. The portable CRGE-nose can be used for in-situ monitoring of CV and PT concentration changes as low as 27.04 and 7.29 ppb in real meats such as pork, beef, lamb and chicken.

Construction of a tunable promoter library to optimize gene expression in Methylomonas sp. DH-1, a methanotroph, and its application to cadaverine production

BACKGROUND

As methane is 84 times more potent than carbon dioxide in exacerbating the greenhouse effect, there is an increasing interest in the utilization of methanotrophic bacteria that can convert harmful methane into various value-added compounds. A recently isolated methanotroph, Methylomonas sp. DH-1, is a promising biofactory platform because of its relatively fast growth. However, the lack of genetic engineering tools hampers its wide use in the bioindustry.

RESULTS

Through three different approaches, we constructed a tunable promoter library comprising 33 promoters that can be used for the metabolic engineering of Methylomonas sp. DH-1. The library had an expression level of 0.24-410% when compared with the strength of the lac promoter. For practical application of the promoter library, we fine-tuned the expressions of cadA and cadB genes, required for cadaverine synthesis and export, respectively. The strain with P_rpmB-cadA and P_DnaA-cadB produced the highest cadaverine titre (18.12 ± 1.06 mg/L) in Methylomonas sp. DH-1, which was up to 2.8-fold higher than that obtained from a non-optimized strain. In addition, cell growth and lysine (a precursor of cadaverine) production assays suggested that gene expression optimization through transcription tuning can afford a balance between the growth and precursor supply.

CONCLUSIONS

The tunable promoter library provides standard and tunable components for gene expression, thereby facilitating the use of methanotrophs, specifically Methylomonas sp. DH-1, as a sustainable cell factory.

Ameliorating end-product inhibition to improve cadaverine production in engineered Escherichia coli and its application in the synthesis of bio-based diisocyanates

Cadaverine is an important C5 platform chemical with a wide range of industrial applications. However, the cadaverine inhibition on the fermenting strain limited its industrial efficiency of the strain. In this study, we report an engineered Escherichia coli strain with high cadaverine productivity that was generated by developing a robust host coupled with metabolic engineering to mitigate cadaverine inhibition. First, a lysine producing E. coli was treated with a combination of radiation (ultraviolet and visible spectrum) and ARTP (atmospheric and room temperature plasma) mutagenesis to obtain a robust host with high cadaverine tolerance. Three mutant targets including HokD, PhnI and PuuR are identified for improved cadaverine tolerance. Further transcriptome analysis suggested that cadaverine suppressed the synthesis of ATP and lysine precursor. Accordingly, the related genes involved in glycolysis and lysine precursor, as well as cadaverine exporter was engineered to release the cadaverine inhibition. The final engineered strain was fed-batch cultured and a titer of 58.7 g/L cadaverine was achieved with a yield of 0.396 g/g, both of which were the highest level reported to date in E. coli. The bio-based cadaverine was purified to >99.6% purity, and successfully used for the synthesis of polyurethane precursor 1,5-pentamethylene diisocyanate (PDI) through the approach of carbamate decomposition.

Production of Cadaverine in Recombinant Corynebacterium glutamicum Overexpressing Lysine Decarboxylase (ldcC) and Response Regulator dr1558

In this study, the response regulator DR1558 from Deinococcus radiodurans was overexpressed in recombinant Corynebacterium glutamicum with lysine decarboxylase (ldcC). The recombinant C. glutamicum strain overexpressing dr1558 and ldcC produced 5.9 g/L of cadaverine by flask cultivation, whereas the control strain overexpressing only ldcC produced 4.5 g/L of cadaverine. To investigate the mechanism underlying the effect of DR1558, the expression levels of genes related to central metabolism and lysine-biosynthesis were analyzed by quantitative-real time polymerase chain reaction. The results showed that phosphoenolpyruvate carboxykinase (pck) was downregulated, and pyruvate kinase (pyk) and other lysine biosynthesis genes were upregulated. Furthermore, in fed-batch fermentation, C. glutamicum coexpressing dr1558 produced 25.14 g/L of cadaverine, a 1.25-fold increase in concentration relative to the control. These results suggested that the heterologous expression of dr1558 may improve the production of biorefinery products by recombinant C. glutamicum.

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.

Au@ZIF-8 SERS paper for food spoilage detection

Putrescine and cadaverine are important volatile indicators for the evaluation of food spoilage. In this study, a metal-organic framework (MOF)-coated surface-enhanced Raman scattering (SERS) paper platform for the detection of putrescine and cadaverine is developed. Au@ zeolite imidazolate framework-8 (ZIF-8) SERS paper is fabricated by the coating of ZIF-8 layer on a Au nanoparticle-impregnated paper that is prepared by dry plasma reduction. The Au@ZIF-8 SERS paper is characterized by scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray diffraction, and N₂ sorption isotherm. The ZIF-8 layer enables the accumulation of gaseous molecules and also provides enhancement of SERS signals. The fluorescence, SERS, and simulation results prove the improved detection ability of the Au@ZIF-8 platform for the volatile molecules. For the selective detection of putrescine and cadaverine, the Au@ZIF-8 SERS paper is functionalized with 4-mercatobenzaldehyde (4-MBA). The 4-MBA molecule acts as a Raman reporter and also a specific receptor for the volatile amine molecules. Using the intensity ratiometric detection of 4-MBA-functionalized Au@ZIF-8 SERS paper, putrescine and cadaverine are quantitatively detected with detection limits of 76.99 and 115.88 parts per billion, respectively. Furthermore, the detection of volatile amine molecules released from spoiled salmon, chicken, beef, and pork samples is demonstrated. It is anticipated that the MOF-coated SERS paper platforms will be applicable not only in food safety but other applications including disease diagnosis and environmental monitoring.

High cell density cultivation enables efficient and sustainable recombinant polyamine production in the microalga Chlamydomonas reinhardtii

Modern chemical industry calls for new resource-efficient and sustainable value chains for production of key base chemicals such as polyamines. The green microalga Chlamydomonas reinhardtii offers great potential as an innovative green-cell factory by combining fast and inexpensive, phototrophic growth with mature genetic engineering. Here, overexpression of recombinant lysine decarboxylases in C. reinhardtii enabled the robust accumulation of the non-native polyamine cadaverine, which serves as building block for bio-polyamides. The issue of low cell densities, limiting most microalgal cultivation processes was resolved by systematically optimizing cultivation parameters. A new, easy-to-apply and fully phototrophic medium enables high cell density cultivations of C. reinhardtii with a 6-fold increase in biomass and cell count (20 g/L biomass dry weight, ~2·10⁸ cells/mL). Application of high cell density cultivations in established photobioreactors resulted in a 10-fold increase of cadaverine yields, with up to 0.24 g/L after 9 days and maximal productivity of 0.1 g/L/d.

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.

Enhanced Cadaverine Production by Engineered Escherichia coli Using Soybean Residue Hydrolysate (SRH) as a Sole Nitrogen Source

An economical source of nitrogen is one of the major limiting factors for sustainable cadaverine production. The utilization potential of soybean residue for enhanced cadaverine production by engineered Escherichia coli DFC1001 was investigated in this study. The SRH from soybean residue could get the protein extraction rate (PE) of 67.51% and the degree of protein hydrolysis (DH) of 22.49%. The protein molecular weights in SRH were mainly distributed in 565 Da (72.28%) and 1252 Da (17.11%). These proteins with small molecular weights and concentrated molecular weight distribution were favorable to be transformed by engineered E. coli DFC1001, and then SRH replaced completely yeast powder as an only nitrogen source for cadaverine production. The maximum cadaverine productivity was 0.52 g/L/h, achieved with a constant speed feeding strategy in the optimized SRH fermentation medium containing an initial total sugar concentration of 30 g/L and exogenous added minerals, which indicated that soybean residue could be a potential feedstock for economic cadaverine production.

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.

Integrated gene engineering synergistically improved substrate-product transport, cofactor generation and gene translation for cadaverine biosynthesis in E. coli

Several approaches for efficient production of cadaverine, a bio-based diamine with broad industrial applications have been explored. Here, Serratia marcescens lysine decarboxylase (SmcadA) was expressed in E. coli; mild surfactants added in biotransformation reactions; the E. coli native lysine/cadaverine antiporter cadB, E. coli pyridoxal kinases pdxK and pdxY overexpressed and synthetic RBS libraries screened. Addition of mild surfactants and overexpression of antiporter cadB increased cadaverine biosynthesis of SmcadA. Moreover, expression of pdxY gene yielded 19.82 g/L in a reaction mixture containing added cofactor precursor pyridoxal (PL), without adding exogenous PLP. The screened synthetic RBS1, applied to fully exploit pdxY gene expression, ultimately resulted in PLP self-sufficiency, producing 27.02 g/L cadaverine using strain T7R1_PL. To boost SmcadA catalytic activity, the designed mutants Arg595Lys and Ser512Ala had significantly improved cumulative cadaverine production of 219.54 and 201.79 g/L respectively compared to the wild-type WT (181.62 g/L), after 20 h reaction. Finally, molecular dynamics simulations for WT and variants indicated that increased flexibility at the binding sites of the protein enhanced residue-ligand interactions, contributing to high cadaverine synthesis. This work demonstrates potential of harnessing different pull factors through integrated gene engineering of efficient biocatalysts and gaining insight into the mechanisms involved through MD simulations.

Metabolic manipulation through CRISPRi and gene deletion to enhance cadaverine production in Escherichia coli

Due to the limiting natural resources, greenhouse effect and global warming crisis, the bio-based chemicals which are environmentally friendly materials have gradually become urgent and important. Cadaverine, a 1,5-diaminopentane (DAP), is widely used as block chemicals for synthesis of biopolymer, which can be produced from lysine by lysine decarboxylase (EC 4.1.1.18) in Escherichia coli. However, the DAP will be further utilized into by-products through downstream genes of speE, puuA, speG and ygjG, which decrease the amount of product. In this study, two approaches including Lambda-Red system for gene knockout, and clustered regularly interspaced short palindromic repeats interference (CRISPRi) for gene knockdown; are explored to manipulate the metabolic flux among 26 genetic E. coli. As a result, CadA driven by inducible T7 promoter accumulated more DAP from CRISPRi targeted on single-gene repressive strains such as BT7AiE, BT7AiP, BT7AiG and BT7AiY. The highest DAP titer and productivity was obtained to 38 g/L and 2.67 g/L/h in BT7AiY (repression of ygjG). We also investigated the co-factor pyridoxal 5'-phosphate (PLP) effect on lysine consumption and DAP production from different E. coli derivatives. In contrast to CRISPRi-mediated strains, 4 genes knockout strain (BT7AdEPGY) deal with 98% lysine consumption and achieved 37.45 g/L DAP and 3.17 g/L/h DAP productivity. The metabolic regulation by CRISPRi is a simple strategy and the results are consistent with gene knockout to manipulate the pathway for DAP production.

High-efficiency and low-cost production of cadaverine from a permeabilized-cell bioconversion by a Lysine-induced engineered Escherichia coli

Cadaverine is the monomer of bio-based nylons polyamide 5.4, 5.6 and 5.10. In this study, a litre-scale integrated strategy was developed for high-efficiency and low-cost production of cadaverine using an engineered Escherichia coli. Firstly, the engineered strain BL21-P_cad-CadA induced by cheap l-lysine-HCl instead of IPTG was constructed. Then the permeabilized cells were served as the biocatalyst for the production of cadaverine, because the enhanced permeability facilitated the mass transfer of the substrate and the release of products. After the replacement of industrial materials and the solution of the scale-up permeabilization process, cadaverine concentration reached 205 g/L with the yield of 92.1% after 20 h in a 2 L bioconversion system, achieving the level of industrial production. Furthermore, the costs of industrial materials for 2 L integrated strategy ($2.78) was only 1/11 of the lab reagents ($30.88). Therefore, the proposed strategy is a promising candidate for the industrial process of cadaverine.

Freshness Evaluation in Chub Mackerel (Scomber japonicus) Using Near-Infrared Spectroscopy Determination of the Cadaverine Content

We analyzed the volatile basic nitrogen content, pH, total viable cell count, and biogenic amine contents in chub mackerel (Scomber japonicus) stored at 5 and 25°C to examine changes in freshness. Among the various parameters, we found the volatile basic nitrogen content had the highest correlation with cadaverine content (r² = 0.72 to 0.88). We also tried to measure cadaverine contents at different times during storage by using near-infrared (NIR) spectroscopy. However, because of the high water content in the fish, we could not obtain meaningful results. Next, we prepared samples for NIR spectroscopy by dilution with 0.1 N HCl, ultrafiltration (3 or 10 kDa) with a glass filter, and dehydration. The samples prepared with the 3-kDa filter had peaks in the NIR spectra between 1,379.3 and 1,388.9 nm, and those prepared with the 10-kDa filter had peaks in the spectra between 1,897.3 and 1,898.6 nm. The correlation coefficient (r²) between the NIR spectroscopy and high-performance liquid chromatography with cadaverine results was 0.98 to 0.99. We concluded that the biogenic amine content could be used to evaluate freshness in fish products, and that NIR measurements could be used to rapidly and accurately determine freshness.

Investigation of biogenic amines content in fermented idli batter during storage

Idli is a cereal-pulse based fermented food. This study profiles the qualitative and quantitative analysis of biogenic amines formed in the fermented idli batter prepared using varying proportions of rice to black gram dal at 1:1, 2:1, 3:1 and 4:1 (w/w) ratios and stored at 30 and 4 °C for 7 days. Histamine, tyramine, putrescine, cadaverine, spermidine, and spermine were investigated for the first time in the idli batter using HPLC technique. Putrescine and cadaverine were the predominant biogenic amines found in both prepared and market samples. Histamine and spermine were not detected in all batter samples. Increasing the proportion of rice in the idli batter resulted in the decrease in the total biogenic amines formed in the fermented batter with batter having more black gram dal (1:1) showing the maximum formation of total biogenic amines. Idli is a safe, easily digestible food to consume as the highest total biogenic amines quantified (366.87 µg/g) in 1:1 variant batter was below the harmful limit (1000 µg/g).

Enhanced production of cadaverine by the addition of hexadecyltrimethylammonium bromide to whole cell system with regeneration of pyridoxal-5'-phosphate and ATP

Cadaverine, also known as 1,5-pentanediamine, is an important platform chemical with a wide range of applications and can be produced either by fermentation or bioconversion. Bioconversion of cadaverine from l-lysine is the preferred method because of its many benefits, including rapid reaction time and an easy downstream process. In our previous study, we replaced pyridoxal-5-phosphate (PLP) with pyridoxal kinase (PdxY) along with pyridoxal (PL) because it could achieve 80% conversion with 0.4 M of l-lysine in 6 h. However, conversion was sharply decreased in the presence of high concentrations of l-lysine (i.e., 1 M), resulting in less than 40% conversion after several hours. In this study, we introduced an ATP regeneration system using polyphosphate kinase (ppk) into systems containing cadaverine decarboxylase (CadA) and PdxY for a sufficient supply of PLP, which resulted in enhanced cadaverine production. In addition, to improve transport efficiency, the use of surfactants was tested. We found that membrane permeabilization via hexadecyltrimethylammonium bromide (CTAB) increased the yield of cadaverine in the presence of high concentrations of l-lysine. By combining these two strategies, the ppk system and addition of CTAB, we enhanced cadaverine production up to 100% with 1 M of l-lysine over the course of 6 h.

Minicircle DNA purification: Performance of chromatographic monoliths bearing lysine and cadaverine ligands

Minicircle DNA (mcDNA) technology is in the vanguard of vectors designed for gene therapy, since the absence of prokaryotic sequences confers to mcDNA higher biosafety in comparison to other DNA vectors. However, the presence of other isoforms and non-recombined parental molecules hampers the isolation of supercoiled (sc) mcDNA with the chromatographic methods already established for plasmid purification. In this work, two monolithic supports were modified with lysine and its decarboxylated derivative, cadaverine, to explore their performance in the sc mcDNA purification. Increasing NaCl gradients and different pH values (from 6 to 9) were tested in both modified monoliths. In general, cadaverine modified support established stronger interactions with mcDNA than lysine modified monolith, at acidic pH. For instance, at pH 6.0 the retention time for RNA and DNA molecules in lysine modified monolith was 11.58 and 14.59, respectively, while for cadaverine modified monolith was 20.32 and 27.12, respectively. The lysine modified monolith was able to successfully isolate sc mcDNA from the lysate sample. However, recovery yield was significantly sacrificed to guarantee high purity levels of sc mcDNA. The cadaverine modified monolith showed better selectivity than the previous monolith, achieving the successful sc mcDNA isolation from the lysate sample. The final sc mcDNA sample, obtained by the column that showed the best performance, was characterized by real-time PCR, presenting 98.4% purity and 78.6% recovery yield. The impurities content, namely genomic DNA, proteins and endotoxins, was found within the criteria established by regulatory agencies. Overall, a simple and practical chromatographic strategy to purify sc mcDNA was for the first time implemented by exploring a modified monolithic column, with no significant reduction on the purity and recovery and without resorting to backbone modification or specific enzymatic digestion. Such features will surely be crucial in the industrial scale-up of this chromatographic strategy since it will not be associated with significant cost-increase.

Biogenic Amine Production by and Phylogenetic Analysis of 23 Photobacterium Species

Photobacterium species are members of the bacterial communities typically associated with scombrotoxin-forming fish. Reclassification and discovery of new Photobacterium species has caused confusion as to which species are capable of biogenic amine production. We analyzed histamine, cadaverine, and putrescine production by 104 Photobacterium strains representing 23 species. The presence of the genes for histidine decarboxylase ( hdc), lysine decarboxylase ( ldc), and ornithine decarboxylase ( odc) was determined by real-time or conventional PCR and whole genome sequencing. Significant histamine production (>200 ppm) was detected in five Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. damselae, and P. phosphoreum. The hdc gene was detected in all of these histamine-producing species except P. phosphoreum. Cadaverine was produced by eight Photobacterium species: P. angustum, P. aquimaris, P. damselae, P. iliopiscarium, P. kishitanii, P. leiognathi, P. mandapamensis, and P. phosphoreum. Putrescine was produced by six Photobacterium species: P. angustum, P. aquimaris, P. kishitanii, P. leiognathi, P. mandapamensis, and Photobacterium sp. Cadaverine production correlated closely with the presence of the ldc gene, but putrescine production did not correlate closely with the presence of the odc gene. Characterization of the biogenic amine production by Photobacterium species will allow identification of these marine bacteria and help ensure that current guidelines account for mitigation of these bacteria.

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

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

Characterizing the glymphatic influx by utilizing intracisternal infusion of fluorescently conjugated cadaverine

AIMS

Accumulating evidence supports that cerebrospinal fluid (CSF) in the subarachnoid space (SAS) could reenter the brain parenchyma via the glymphatic influx. The present study was designed to characterize the detailed pathway of subarachnoid CSF influx by using a novel CSF tracer.

MAIN METHODS

Fluorescently conjugated cadaverine (A488-ca), for the first time, was employed to investigate CSF movement in the brain. Following intracisternal infusion of CSF tracers, mice brain was sliced and prepared for fluorescence imaging. Some brain sections were immunostained in order to observe tracer distribution and cellular uptake.

KEY FINDINGS

A488-ca moved into the brain parenchyma rapidly, and the influx was time and region dependent. A488-ca entered the mice brain more readily and spread more widely than another commonly used CSF tracer-fluorescently conjugated ovalbumin (OA-45). Furthermore, A488-ca could enter the brain parenchyma either along the paravascular space or across the pial surface. Suppression of glymphatic transport by administration with acetazolamide strikingly reduced the influx of A488-ca. More importantly, relative to OA-45 largely remained in the extracellular space, A488-ca exhibited obvious cellular uptake by astrocytes surrounding the blood vessels and neurons in the cerebral cortex.

SIGNIFICANCE

Subarachnoid CSF could flow into the brain parenchyma via the glymphatic influx, in which the transcellular pathway was faithfully traced by intracisternal infusion with fluorescently conjugated cadaverine. These observations extend our comprehension on the glymphatic influx pathway.

Enhancement of the thermal and alkaline pH stability of Escherichia coli lysine decarboxylase for efficient cadaverine production

OBJECTIVE

To enhance the thermal and alkaline pH stability of the lysine decarboxylase from Escherichia coli (CadA) by engineering the decameric interface and explore its potential for industrial applications.

RESULTS

The mutant T88S was designed for improved structural stability by computational analysis. The optimal pH and temperature of T88S were 7.0 and 55 °C (5.5 and 50 °C for wild-type). T88S showed higher thermostability with a 2.9-fold increase in the half-life at 70 °C (from 11 to 32 min) and increased melting temperature (from 76 to 78 °C). Additionally, the specific activity and pH stability (residual activity after 10 h incubation) of T88S at pH 8.0 were increased to 164 U/mg and 78% (58 U/mg and 57% for wild-type). The productivity of cadaverine with T88S (284 g L-lysine L^-1 and 5 g DCW L^-1) was 40 g L^-1 h^-1, in contrast to 28 g L^-1 h^-1 with wild-type.

CONCLUSION

The mutant T88S showed high thermostability, pH stability, and activity at alkaline pH, indicating that this mutant is a promising biocatalyst for industrial production of cadaverine.

Microbial Production of Amino Acid-Related Compounds

Corynebacterium glutamicum is the workhorse of the production of proteinogenic amino acids used in food and feed biotechnology. After more than 50 years of safe amino acid production, C. glutamicum has recently also been engineered for the production of amino acid-derived compounds, which find various applications, e.g., as synthons for the chemical industry in several markets including the polymer market. The amino acid-derived compounds such as non-proteinogenic ω-amino acids, α,ω-diamines, and cyclic or hydroxylated amino acids have similar carbon backbones and functional groups as their amino acid precursors. Decarboxylation of amino acids may yield ω-amino acids such as β-alanine, γ-aminobutyrate, and δ-aminovalerate as well as α,ω-diamines such as putrescine and cadaverine. Since transamination is the final step in several amino acid biosynthesis pathways, 2-keto acids as immediate amino acid precursors are also amenable to production using recombinant C. glutamicum strains. Approaches for metabolic engineering of C. glutamicum for production of amino acid-derived compounds will be described, and where applicable, production from alternative carbon sources or use of genome streamline will be referred to. The excellent large-scale fermentation experience with C. glutamicum offers the possibility that these amino acid-derived speciality products may enter large-volume markets.

Safety assessment of commensal enterococci from dogs

Enterococci form a complex, diverse, and very important group of bacteria from the technological and food safety aspect, or from the health-improving aspect as probiotics. Generally, enterococci are considered to be of low pathogenic potential, which is associated mostly with clinical strains. In these strains, production of virulence factors as well as resistance to many antimicrobial drugs could complicate treatment of nosocomial infections. Because there is a lack of information on incidence of these attributes in animal commensal enterococci, we screened 160 strains originating from feces of clinically healthy dogs in Eastern Slovakia (n = 105). The predominant species were Enterococcus faecium (57.5%) followed by Enterococcus faecalis (21.9%), and Enterococcus hirae (17.5%), while Enterococcus casseliflavus (1.9%) and Enterococcus mundtii (1.2%) rarely occurred. Among the tested antibiotics, gentamicin (high level) was the most effective drug against canine enterococci (95% of isolates were sensitive). In contrast, the highest resistance recorded (71.9%) was to teicoplanin. PCR screening showed the highest incidence of virulence genes in E. faecalis species. The most frequently detected were genes encoding adhesins efa _Afm and efa _Afs and sex pheromone cpd. IS16 gene, a marker specific for hospital strains, appeared in nine E. faecium strains. No strain was positive for DNase activity, 8.8% of the isolated strains showed gelatinase activity, and almost 100% strains produced tyramine. It seems commensal-derived enterococci from dogs could also to some extent be potential reservoir of risk factors for other microbiota or organisms.

Metabolomics and neuroanatomical evaluation of post-mortem changes in the hippocampus

Understanding the human brain is the ultimate goal in neuroscience, but this is extremely challenging in part due to the fact that brain tissue obtained from autopsy is practically the only source of normal brain tissue and also since changes at different levels of biological organization (genetic, molecular, biochemical, anatomical) occur after death due to multiple mechanisms. Here we used metabolomic and anatomical techniques to study the possible relationship between post-mortem time (PT)-induced changes that may occur at both the metabolomics and anatomical levels in the same brains. Our experiments have mainly focused on the hippocampus of the mouse. We found significant metabolomic changes at 2 h PT, whereas the integrity of neurons and glia, at the anatomical/ neurochemical level, was not significantly altered during the first 5 h PT for the majority of histological markers.

Synthetic redesign of Escherichia coli for cadaverine production from galactose

BACKGROUND

With increasing concerns over the environment, biological production of cadaverine has been suggested as an alternative route to replace polyamides generated from the petroleum-based process. For an ideal bioprocess, cadaverine should be produced with high yield and productivity from various sugars abundant in biomass. However, most microorganisms are not able to efficiently metabolize other biomass-derived sugars as fast as glucose. This results in reduced growth rate and low carbon flux toward the production of desired bio-chemicals. Thus, redesign of microorganisms is necessary for utilizing those carbon sources with enhanced carbon flux and product formation.

RESULTS

In this study, we engineered Escherichia coli to produce cadaverine with rapid assimilation of galactose, a promising future feedstock. To achieve this, genes related to the metabolic pathway were maximally expressed to amplify the flux toward cadaverine production via synthetic expression cassettes consisting of predictive and quantitative genetic parts (promoters, 5'-untranslated regions, and terminators). Furthermore, the feedback inhibition of metabolic enzymes and degradation/re-uptake pathways was inactivated to robustly produce cadaverine. Finally, the resultant strain, DHK4, produced 8.80 g/L cadaverine with high yield (0.170 g/g) and productivity (0.293 g/L/h) during fed-batch fermentation, which was similar to or better than the previous glucose fermentation.

CONCLUSIONS

Taken together, synthetic redesign of a microorganism with predictive and quantitative genetic parts is a prerequisite for converting sugars from abundant biomass into desired platform chemicals. This is the first report to produce cadaverine from galactose. Moreover, the yield (0.170 g/g) was the highest among engineered E. coli systems.

A fluorescence anisotropy-based assay for determining the activity of tissue transglutaminase

Tissue transglutaminase (TGase 2) is the most abundantly expressed enzyme of the transglutaminase family and involved in a large variety of pathological processes, such as neurodegenerative diseases, disorders related to autoimmunity and inflammation as well as tumor growth, progression and metastasis. As a result, TGase 2 represents an attractive target for drug discovery and development, which requires assays that allow for the characterization of modulating agents and are appropriate for high-throughput screening. Herein, we report a fluorescence anisotropy-based approach for the determination of TGase 2's transamidase activity, following the time-dependent increase in fluorescence anisotropy due to the enzyme-catalyzed incorporation of fluorescein- and rhodamine B-conjugated cadaverines 1-3 (acyl acceptor substrates) into N,N-dimethylated casein (acyl donor substrate). These cadaverine derivatives 1-3 were obtained by solid-phase synthesis. To allow efficient conjugation of the rhodamine B moiety, different linkers providing secondary amine functions, such as sarcosyl and isonipecotyl, were introduced between the cadaverine and xanthenyl entities in compounds 2 and 3, respectively, with acyl acceptor 3 showing the most optimal substrate properties of the compounds investigated. The assay was validated for the search of both irreversible and reversible TGase 2 inhibitors using the inactivators iodoacetamide and a recently published L-lysine-derived acrylamide and the allosteric binder GTP, respectively. In addition, the fluorescence anisotropy-based method was proven to be suitable for high-throughput screening (Z' factor of 0.86) and represents a non-radioactive and highly sensitive assay for determining the active TGase 2 concentration.

Biotransformation of lysine into cadaverine using barium alginate-immobilized Escherichia coli overexpressing CadA

In this study, Escherichia coli cells overexpressing lysine decarboxylase (CadA) were used for cadaverine production. Barium alginate was selected as a matrix for immobilization of E. coli YH91. Free cells and immobilized cells (IC) were characterized for their physiochemical properties, and the optimum pH and temperature were determined as 6 and 37 °C, respectively. Immobilized cells were three times more thermally stable compared to free cells at the optimum temperature and had a half-life (t 1/2) of 131 h. The free cells lost most of lysine decarboxylase activity after nine cycles, but in contrast immobilized cells retained 56% of their residual activity even after the 18th cycle. The immobilized cells gave a maximum production of cadaverine (75.8 g/L) with 84% conversion.

Production of carbon-13-labeled cadaverine by engineered Corynebacterium glutamicum using carbon-13-labeled methanol as co-substrate

Methanol, a one-carbon compound, can be utilized by a variety of bacteria and other organisms as carbon and energy source and is regarded as a promising substrate for biotechnological production. In this study, a strain of non-methylotrophic Corynebacterium glutamicum, which was able to produce the polyamide building block cadaverine as non-native product, was engineered for co-utilization of methanol. Expression of the gene encoding NAD+-dependent methanol dehydrogenase (Mdh) from the natural methylotroph Bacillus methanolicus increased methanol oxidation. Deletion of the endogenous aldehyde dehydrogenase genes ald and fadH prevented methanol oxidation to carbon dioxide and formaldehyde detoxification via the linear formaldehyde dissimilation pathway. Heterologous expression of genes for the key enzymes hexulose-6-phosphate synthase and 6-phospho-3-hexuloisomerase of the ribulose monophosphate (RuMP) pathway in this strain restored growth in the presence of methanol or formaldehyde, which suggested efficient formaldehyde detoxification involving RuMP key enzymes. While growth with methanol as sole carbon source was not observed, the fate of 13C-methanol added as co-substrate to sugars was followed and the isotopologue distribution indicated incorporation into central metabolites and in vivo activity of the RuMP pathway. In addition, 13C-label from methanol was traced to the secreted product cadaverine. Thus, this synthetic biology approach led to a C. glutamicum strain that converted the non-natural carbon substrate methanol at least partially to the non-native product cadaverine.

Enzymatic assay to test diamines produced by vaginal bacteria

An enzymatic assay was developed to determine the concentration of diamines (DA) in clinical samples of vaginal fluids. Putrescine and cadaverine are DA produced by anaerobic bacteria and are typically present in the vaginal fluids of women with an abnormal microbiota, as occurs in bacterial vaginosis. The vaginal DA (VADA) assay is based on the enzyme diamine oxidase which reacts with putrescine and cadaverine to produce H2O2 in a quantitative manner. H2O2 concentration is measured spectrophotometrically by a chromogenic reaction catalyzed by horseradish peroxidase. The VADA assay proved to be capable of detecting DA concentrations as low as 4 mM and showed a dose-response relationship which was linear over DA concentrations ranging from 4 to 256 mM. Using clinical samples it was possible to show that the VADA assay can be performed on human vaginal swabs and that the mean DA concentration is significantly higher in samples positive for microbial pathogens.

Determination of biogenic amines by high-performance liquid chromatography (HPLC-DAD) in probiotic cow's and goat's fermented milks and acceptance

This study evaluated the presence of biogenic amines in fermented cow's and goat's milks containing probiotic bacteria, during the first 10 days of chilled storage (4 ± 2°C), when the probiotic strains are most viable. The overall acceptance of both fermented milks, produced using the same starter culture and probiotics, was tested. In both products, the initially high levels of tyramine (560 mg kg⁻¹ means for both fermented milks), the predominant biogenic amine, increased during the storage period, which may be considered this amine as a quality index for fermented milks. The other principal biogenic amines (putrescine, cadaverine, histamine, and spermidine) were produced on days 1–5 of storage, and thereafter decreased. At the end of the 10th day, these amines, respectively, showed values of fermented cow's milk 20.26, 29.09, 17.97, and 82.07 mg kg⁻¹; and values of fermented goat's milk 22.92, 29.09, 34.85, and 53.85 mg kg⁻¹, in fermented cow's and goat's milk. Fermented cow's milk was well accepted compared to fermented goat's milk. The results suggested that the content of biogenic amines may be a criterion for selecting lactic acid bacteria used to produce fermented milks.

Biogenic amines, amino acids and microflora changes in Indian mackerel (Rastrellinger kanagurta) stored at ambient (25-29 °C) and ice temperature (0 °C)

Biogenic amines formation in Indian mackerel of tropical region was investigated during storage at ambient (25-29 °C) and ice temperature (0 °C) in relation with changes of amino acids content and amines forming bacteria. All amines increased significantly during storage at two temperatures except for spermidine and spermine. Histamine concentration of 363.5 ppm was detected after 16 h stored at ambient temperature. Aerobic plate count of fish stored at ambient temperature reached 6.98 log CFU g(-1) after 16 h, close to the upper limit (7 log CFU g(-1)) suggested by International Commission on the Microbiological Specifications for Foods (ICMSF). However, proper icing procedure retarded the formation of histamine effectively, resulting only 8.31 ppm after 16 days of ice storage. Aerobic plate count of 5.99 and 7.72 log CFU g(-1) were recorded for fish stored in ice after 16 days and ambient temperature after 20 h, respectively. Histamine exhibited high correlation with histidine (r(2) = -0.963, P < 0.01) as well as cadaverine with lysine (r(2) = -0.750, P < 0.05). However, tyramine-tyrosine demonstrated a weaker relationship (r(2) = -0.138, P > 0.05). As storage time progressed, the amines forming bacteria grew significantly except for that stored in ice.

Arabidopsis mutant plants with diverse defects in polyamine metabolism show unequal sensitivity to exogenous cadaverine probably based on their spermine content

Arabidopsis plants do not synthesize the polyamine cadaverine, a five carbon-chain diamine and structural analog of putrescine. Mutants defective in polyamine metabolic genes were exposed to exogenous cadaverine. Spermine-deficient spms mutant grew well while a T-DNA insertion mutant (pao4-1) of polyamine oxidase (PAO) 4 was severely inhibited in root growth compared to wild type (WT) or other pao loss-of-function mutants. To understand the molecular basis of this phenomenon, polyamine contents of WT, spms and pao4-1 plants treated with cadaverine were analyzed. Putrescine contents increased in all the three plants, and spermidine contents decreased in WT and pao4-1 but not in spms. Spermine contents increased in WT and pao4-1. As there were good correlations between putrescine (or spermine) contents and the degree of root growth inhibition, effects of exogenously added putrescine and spermine were examined. Spermine mimicked the original phenomenon, whereas high levels of putrescine evenly inhibited root growth, suggesting that cadaverine-induced spermine accumulation may explain the phenomenon. We also tested growth response of cadaverine-treated WT and pao4-1 plants to NaCl and found that spermine-accumulated pao4-1 plant was not NaCl tolerant. Based on the results, the effect of cadaverine on Arabidopsis growth and the role of PAO during NaCl stress are discussed.

Simultaneous determination of cadaverine and putrescine using a disposable monoamine oxidase based biosensor

The selective and simultaneous amperometric determination of putrescine (Put) and cadaverine (Cad) has been carried out using a novel design of screen-printed carbon electrode (SPCE) with two working electrodes connected in array mode. A mixture of 3% of tetrathiafulvalene (TTF), as mediator, and carbon ink was used for the construction of the screen-printed working electrode. The employment of different amounts of monoamine oxidase (MAO) enzyme on these modified TTF/SPCEs and the use of gold nanoparticles (AuNPs) allowed performing the simultaneous determination of both analytes. The amperometric detection has been performed by measuring the oxidation current of the mediator at a potential of+250 mV vs. screen-printed Ag/AgCl reference electrode. A linear response in the Cad concentration range from 19.6 till 107.1 µM and from 9.9 till 74.1 μM for Put was obtained at the MAO/AuNPs/TTF/SPCE biosensor. This device showed a capability of detection of 9.9 and 19.9±0.9 µM (n=4 α=β=0.05) and a precision of 4.9% and 10.3% in terms of relative standard deviation for Put and Cad, respectively. The developed biosensor was successfully applied to the simultaneous determination of Put and Cad in octopus samples.