Recent advances in microbial ε-poly-L-lysine fermentation and its diverse applications

Enhancing the Production of ε-Poly-l-Lysine by Engineering the Sucrose Metabolism Pathway in Streptomyces albulus PD-1 Using Cane Molasses

Cane molasses, a sugar-rich agro-industrial byproduct, was used to enhance the production of ε-poly-l-lysine (ε-PL) in Streptomyces albulus PD-1 as a cost-effective carbon source. The sucrose metabolism pathway was engineered by heterologously expressing sucrose-6-phosphate hydrolase from Escherichia coli W. The optimization of various promoters identified the SP44 promoter, increasing the total sugar utilization rate by 2.76-fold compared with the ermEp* promoter. Additionally, adaptive laboratory evolution improved the total sugar utilization rate. The evolved strain achieved an ε-PL titer of 2.65 ± 0.15 g/L in flask experiments, increasing the ε-PL titer by 7.16-fold compared with the unevolved strain. Comparative transcriptomic analyses revealed that the enhanced tolerance of the evolved strain to high concentrations of cane molasses was primarily due to modifications in the sucrose metabolism pathways, microbial metabolism in heavy metals and phenols, and the amino acids transport and metabolic pathways. These changes enabled more efficient ε-PL production. During fed-batch fermentation in a 5-L fermentor using a concentration of 50 g/L cane molasses, the ε-PL titer reached 36.88 ± 0.62 g/L, and dry cell weight was 41.1 ± 1.0 g/L. This study illustrates that cane molasses is an economical carbon source for producing ε-PL on an industrial scale.

Optimizing Escherichia coli strains and fermentation processes for enhanced L-lysine production: a review

lysine is an essential amino acid with significant importance, widely used in the food, feed, and pharmaceutical industries. To meet the increasing demand, microbial fermentation has emerged as an effective and sustainable method for L-lysine production. Escherichia coli has become one of the primary microorganisms for industrial L-lysine production due to its rapid growth, ease of genetic manipulation, and high production efficiency. This paper reviews the recent advances in E. coli strain engineering and fermentation process optimization for L-lysine production. Additionally, it discusses potential technological breakthroughs and challenges in E. coli-based L-lysine production, offering directions for future research to support industrial-scale production.

Macrophage metabolic reprogramming-based diabetic infected bone defect/bone reconstruction though multi-function silk hydrogel with exosome release

Diabetic infected bone defects (DIBD) with abnormal immune metabolism are prone to the hard-to-treat bacterial infections and delayed bone regeneration, which present significant challenges in clinic. Control of immune metabolism is believed to be important in regulating fundamental immunological processes. Here, we developed a macrophage metabolic reprogramming hydrogel composed of modified silk fibroin (Silk-6) and poly-l-lysine (ε-PL) and further integrated with M2 Macrophage-derived Exo (M2-Exo), named Silk-6/ε-PL@Exo. This degradable hydrogel showed a broad-spectrum antibacterial performance against both Gram-positive and -negative bacteria. More importantly, the release of M2-Exo from Silk-6/ε-PL@Exo could target M1 macrophages, modulating the activity of the key enzyme hexokinase II (HK2) to control the inflammation-related NF-κB pathway, alleviate lactate accumulation, and inhibit glycolysis to normalize the cycle, thereby promoting M1-to-M2 balance. Using a rat model of DIBD, Silk-6/ε-PL@Exo hydrogel promoted infection control, balanced immune responses and accelerated the bone defect healing. Overall, this study demonstrates that this Silk-6/ε-PL @Exo is a promising filler biomaterial with multi-function to treat DIBD and emphasizes the importance of metabolic reprogramming in bone regeneration.

Synergistic Polymer Coatings with Antibacterial and Antiviral Properties for Healthcare Applications

The role of frequently touched surfaces in the transmission of infectious diseases is well-documented, and the urgent need for effective surface technologies with antipathogen activity has been highlighted by the recent global pandemic and rise in antimicrobial resistance. Here, we have explored combinations of up to 3 different classes of compounds within a polymeric matrix to enable the fabrication of coatings with broad-spectrum activity. Compounds were either based on metals or metal oxides, namely, copper, silver, and copper oxide, essential oils, namely, cinnamaldehyde, tea tree oil, and carvacrol oil, or cationic polymers, namely, poly(ε-lysine) and poly(hexamethylene biguanide). These compounds were mixed into a polymer matrix, coated, and dried to yield durable coatings. Coatings containing up to 7.5% (w/w) of the compounds were assessed in the zone of inhibition and biofilm assays using Staphylococcus aureus and Pseudomonas aeruginosa, as well as infectivity assays using human coronavirus OC43. Our data demonstrate that a selected combination of additives was able to provide a 5-log reduction in the colony-forming units of both bacteria and a 4-log reduction in viral infectivity. This simple but highly effective technology is expected to find applications in environments such as hospitals, aged care facilities, or public transport.

Multi-step strategies for synergistic treatment of urinary tract infections based on D-xylose-decorated antimicrobial peptide carbon dots

Urinary tract infections (UTIs) caused by Uropathogenic Escherichia coli (UPEC), often reoccur due to the formation of intracellular bacterial colonies (IBCs) and antibiotic resistance. Given the significance of YadC for UPEC infection in our previous study, we developed D-xylose-decorated ɛ-poly-L-lysine (εPL)-based carbon dots (D-xyl@εPLCDs) that can be traced, and employed multi-step approaches to elucidate the functional roles of D-xyl@εPLCDs in UPEC infection. Compared to undecorated particles, D-xyl@εPLCDs demonstrate YadC-dependent bacterial targeting and exhibit enhanced bactericidal activities both intracellularly and extracellularly. Moreover, pre-treatment of D-xyl@εPLCDs before infection blocked the subsequent adhesion and invasion of UPEC to bladder epithelial cells 5637. Increase of ROS production and innate immune responses were observed in bladder epithelial cells 5637 treated with D-xyl@εPLCDs. In addition, treatment of D-xyl@εPLCDs post-infection facilitated clearance of UPEC in the bladders of the UTI mouse model, and reduced ultimate number of neutrophils, macrophages and inflammatory responses raised by invaded bacteria. Collectively, we presented a comprehensive evaluating system to show that D-xyl@εPLCDs exhibits superior bactericidal effects against UPEC, making them a promising candidate for drug development in clinical UTI therapeutics.

Graphene oxide/ε-poly-L-lysine self-assembled functionalized coatings improve the biocompatibility and antibacterial properties of titanium implants

The construction of an antibacterial biological coating on titanium surface plays an important role in the long-term stability of oral implant restoration. Graphene oxide (GO) has been widely studied because of its excellent antibacterial properties and osteogenic activity. However, striking a balance between its biological toxicity and antibacterial properties remains a significant challenge with GO. ε-poly-L-lysine (PLL) has broad-spectrum antibacterial activity and ultra-high safety performance. Using Layer-by-layer self-assembly technology (LBL), different layers of PLL/GO coatings and GO self-assembly coatings were assembled on the surface of titanium sheet. The materials were characterized using scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and contact angle test. The antibacterial properties of Porphyromonas gingivalis (P.g.) were analyzed through SEM, coated plate experiment, and inhibition zone experiment. CCK-8 was used to determine the cytotoxicity of the material to MC3T3 cells, and zebrafish larvae and embryos were used to determine the developmental toxicity and inflammatory effects of the material. The results show that the combined assembly of 20 layers of GO and PLL exhibits good antibacterial properties and no biological toxicity, suggesting a potential application for a titanium-based implant modification scheme.

Design and optimization of ε-poly-l-lysine with specific functions for diverse applications

ε-Poly-l-lysine (ε-PL) is a natural homo-poly(amino acid) which can be produced by microorganisms. With the advantages in broad-spectrum antimicrobial activity, biodegradability, and biocompatibility, ε-PL has been widely used as a preservative in the food industry. Different molecular architectures endow ε-PL and ε-PL-based materials with versatile applications. However, the microbial synthesis of ε-PL is currently limited by low efficiencies in genetic engineering and molecular architecture modification. This review presents recent advances in ε-PL production and molecular architecture modification of microbial ε-PL, with a focus on the current challenges and solutions for the improvement of the productivity and diversity of ε-PL. In addition, we highlight recent examples where ε-PL has been applied to expand the versability of edible films and nanoparticles in various applications. Commercial production and the challenges and future research directions in ε-PL biosynthesis are also discussed. Currently, although the main use of ε-PL is as a food preservative, ε-PL and ε-PL-based polymers have shown excellent application potential in biomedical fields. With the development of synthetic biology, the design and synthesis of ε-PL with a customized molecular architecture are possible in the near future. ε-PL-based polymers with specific functions will be a new trend in biopolymer manufacturing.

Metabolic perturbation of Streptomyces albulus by introducing NADP-dependent glyceraldehyde 3-phosphate dehydrogenase

The available resources of Streptomyces represent a valuable repository of bioactive natural products that warrant exploration. Streptomyces albulus is primarily utilized in the industrial synthesis of ε-poly-L-lysine (ε-PL). In this study, the NADP-dependent glyceraldehyde 3-phosphate dehydrogenase (GapN) from Streptococcus mutans was heterologously expressed in S. albulus CICC11022, leading to elevated intracellular NADPH levels and reduced NADH and ATP concentrations. The resulting perturbation of S. albulus metabolism was comprehensively analyzed using transcriptomic and metabolomic methodologies. A decrease in production of ε-PL was observed. The expression of gapN significantly impacted on 23 gene clusters responsible for the biosynthesis of secondary metabolites. A comprehensive analysis revealed a total of 21 metabolites exhibiting elevated levels both intracellularly and extracellularly in the gapN expressing strain compared to those in the control strain. These findings underscore the potential of S. albulus to generate diverse bioactive natural products, thus offering valuable insights for the utilization of known Streptomyces resources through genetic manipulation.

Auricularia auricula Anionic Polysaccharide Nanoparticles for Gastrointestinal Delivery of Pinus koraiensis Polyphenol Used in Bone Protection under Weightlessness

Auricularia auricula polysaccharides used in Pinus koraiensis polyphenol encapsulation and delivery under weightlessness are rarely reported. In this study, an anionic polysaccharide fragment named AAP Iα with a molecular weight of 133.304 kDa was isolated and purified to construct a polyphenol encapsulation system. Nanoparticles named NPs-PP loaded with a rough surface for Pinus koraiensis polyphenol (PP) delivery were fabricated by AAP Iα and ε-poly-L-lysine (ε-PL). SEM and the DLS tracking method were used to observe continuous changes in AAP Iα, ε-PL and PP on the nanoparticles' rough surface assembly, as well as the dispersion and stability. Hydrophilic, monodisperse and highly negative charged nanoparticles can be formed at AAP Iα 0.8 mg/mL, ε-PL 20 μg/mL and PP 80 μg/mL. FT-IR was used to determine their electrostatic interactions. Release kinetic studies showed that nanoparticles had an ideal gastrointestinal delivery effect. NPs-PP loaded were assembled through electrostatic interactions between polyelectrolytes after hydrogen bonding formation in PP-AAP Iα and PP-ε-PL, respectively. Colon adhesion properties and PP delivery in vivo of nanoparticles showed that NPs-PP loaded had high adhesion efficiency to the colonic mucosa under simulated microgravity and could enhance PP bioavailability. These results suggest that AAP Iα can be used in PP encapsulation and delivery under microgravity in astronaut food additives.

Additive effect of the Streptomyces albus XJC2-1 and dimethomorph control pepper blight (Capsicum annuum L.)

BACKGROUND

Pepper blight, caused by Phytophthora capsici, is a destructive soilborne disease, which poses a serious threat to pepper, Capsicum annuum L., production. Chemical fungicides, which mainly are used to control pepper blight, have a negative effect on the environment, rendering biological control as a promising alternative to maintain the balance between ecology and pest management. The purpose of this study was to screen the biocontrol bacteria, reduce the dosage of fungicides and increase the stability of biocontrol bacteria, and to find the mixing ratio of biocontrol bacteria and fungicides giving the best control effect.

RESULTS

We isolated actinomycetes strains from the soil surrounding the roots of healthy pepper plants amongst field-grown plants infected with P. capsici. Of these, Streptomyces albus XJC2-1 showed a strong inhibition effect on the growth of P. capsici, with an inhibition rate of ≤85%. XJC2-1 effectively inhibited the formation of sporangium and release of zoospores of P. capsici as well as directly destroyed its hyphae, to achieve the inhibitory effect. Transcriptomic profiling of pepper leaves, postirrigation of plants with the XJC2-1 fermentation broth, revealed upregulation of genes related to the photosynthesis pathway in pepper. Furthermore, XJC2-1 treatment improved the net photosynthetic rate and intercellular CO2 concentration, thereby improving the pepper plant's resistance to pathogens. The combination of XJC2-1 with the fungicide dimethomorph (8 μg mL-1 ) displayed strong synergism in inhibition of P. capsici infection, with a control efficiency as high as 75.16%, thus providing a basis for its application in the field.

CONCLUSION

Our study demonstrated that S. albus XJC2-1 inhibited Phytophthora pathogens from infecting pepper plants and enhanced plant host resistance. The combination of XJC2-1 and dimethomorph displayed a more stable and stronger control effect on pepper blight, showing potential for the future application of XJC2-1 in the field of biological control. © 2023 Society of Chemical Industry.

ε-Polylysine Derived from Marine Bacteria-A Possible Natural Preservative for Raw Milk Storage

Despite the fact that researchers have been working on the preservation of raw milk at room temperature for several decades, most of the processes are limited to the use of chemical preservatives. One of the major problems of raw milk self-life is its spoilage at ambient temperature during the summer season. Therefore, in the present study, research has been conducted to control raw milk spoilage at 4 °C and 35 °C (considered in different regions’ ambient temperatures). ε-Polylysine, a natural preservative approved for food use, was isolated from the fermentation broth of Bacillus licheniformis PL26 grown in an M3G medium, and its antimicrobial preservation properties for milk applications were tested. The raw milk samples containing 0.02% w/v ε-polylysine could be stored at 4 °C for up to 16 days without spoilage, however, raw milk samples without ε-polylysine as preservative spoiled on the 8th day even at 4 °C refrigeration conditions. Raw milk containing 0.02% ε-polylysine in combination with 0.2% sodium bicarbonate (added to avoid acidification) could be stored at ambient temperature (35 °C) for up to 48 h. The changes in milk composition, especially of the casein, lactose, and fat stability, during storage under different conditions with/without ε-polylysine, were studied as well. The present study proves that ε-polylysine can be successfully used as a new biopreservative. Therefore, for the dairy industry, a natural preservative to store milk at room temperature during the summer season, replacing synthetic preservatives derived from renewable sources, can be proposed. Once again, marine bacteria seem to be one of the promising sustainable and renewable sources of biologically active compounds such as new food biopreservatives

Carboxylated ε-Poly-l-lysine Improves Post-Thaw Quality, Mitochondrial Functions and Antioxidant Defense of Goat Cryopreserved Sperm

Carboxylated ε-poly-l-lysine (CPLL), a novel cryoprotectant, can protect the sperm membranes by inhibiting ice crystal formation during the cryopreservation process. The present study was conducted to investigate the consequence of CPLL supplementation on the post-thaw quality of cryopreserved goat sperm. For this, different doses (0, 0.5%, 1%, 1.5%, and 2%; v/v) of CPLL were added to the cryopreservation medium, and the motility, membrane and acrosome integrity, mitochondrial membrane potential (MMP), ATP level, ROS production, anti-oxidant defense system, malondialdehyde (MDA) level, and apoptosis in post-thaw sperm were evaluated. It was observed that the addition of 1% CPLL significantly (p < 0.05) increased the total motility, membrane integrity, acrosome integrity, and catalase (CAT) activity of post-thaw sperm compared to those of control and other CPLL doses. The ATP content was observed significantly (p < 0.05) higher in 0.5% and 1% CPLL, however, the SOD activity and progressive motility were significantly (p < 0.05) increased by adding CPLL at 1% and 1.5% level. Moreover, the addition of CPLL at 1% dose not only showed a lower percentage of apoptosis, but also significantly (p < 0.05) increased the MMP while reducing ROS production and MDA levels compared to those of other CPLL doses and/or control. Therefore, it is clear that the supplementation of 1% CPLL can remarkably improve the post-thaw goat sperm motility, membrane and acrosome integrity, antioxidant abundance, mitochondrial potentials, and ATP supply by protecting the sperm from cryodamage and undergoing apoptosis. These findings will provide novel insights into sperm cryobiology.

Transcriptomic and metabolomic analyses for providing insights into the influence of polylysine synthetase on the metabolism of Streptomyces albulus

ε-poly-L-lysine (ε-PL) is the main secondary metabolite of Streptomyces albulus, and it is widely used in the food industry. Polylysine synthetase (Pls) is the last enzyme in the ε-PL biosynthetic pathway. Our previous study revealed that Pls overexpressed in S. albulus CICC11022 result in the efficient production of ε-PL. In this study, a Pls gene knockout strain was initially constructed. Then, genomic, transcriptomic and metabolomic approaches were integrated to study the effects of the high expression and knockout of Pls on the gene expression and metabolite synthesis of S. albulus. The high expression of Pls resulted in 598 significantly differentially expressed genes (DEGs) and 425 known differential metabolites, whereas the inactivation of Pls resulted in 868 significant DEGs and 374 known differential metabolites. The expressions of 8 and 35 genes were negatively and positively associated with the Pls expression, respectively. Subsequently, the influence mechanism of the high expression and inactivation of Pls on the ε-PL biosynthetic pathway was elucidated. Twelve metabolites with 30% decreased yield in the high-expression strain of Pls but 30% increased production in the Pls knockout strain were identified. These results demonstrate the influence of Pls on the metabolism of S. albulus. The present work can provide the theoretical basis for improving the production capacity of ε-PL by means of metabolic engineering or developing bioactive substances derived from S. albulus.