Occurrence, biosynthesis, biodegradation, and industrial and medical applications of a naturally occurring ε-poly-L-lysine

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.

Silver and Antimicrobial Polymer Nanocomplexes to Enhance Biocidal Effects

Antimicrobial resistance has become a major problem over the years and threatens to remain in the future, at least until a solution is found. Silver nanoparticles (Ag-NPs) and antimicrobial polymers (APs) are known for their antimicrobial properties and can be considered an alternative approach to fighting resistant microorganisms. Hence, the main goal of this research is to shed some light on the antimicrobial properties of Ag-NPs and APs (chitosan (CH), poly-L-lysine (PLL), ε-poly-L-lysine (ε-PLL), and dopamine (DA)) when used alone and complexed to explore the potential enhancement of the antimicrobial effect of the combination Ag-NPs + Aps. The resultant nanocomplexes were chemically and morphologically characterized by UV-visible spectra, zeta potential, transmission electron microscopy, and Fourier-transform infrared spectroscopy. Moreover, the Ag-NPs, APs, and Ag-NPs + APs nanocomplexes were tested against Gram-positive Staphylococcus aureus (S. aureus) and the Gram-negative Escherichia coli (E. coli) bacteria, as well as the fungi Candida albicans (C. albicans). Overall, the antimicrobial results showed potentiation of the activity of the nanocomplexes with a focus on C. albicans. For the biofilm eradication ability, Ag-NPs and Ag-NPs + DA were able to significantly remove S. aureus preformed biofilm, and Ag-NPs + CH were able to significantly destroy C. albicans biofilm, with both performing better than Ag-NPs alone. Overall, we have proven the successful conjugation of Ag-NPs and APs, with some of these formulations showing potential to be further investigated for the treatment of microbial infections.

Biosynthesis of Antifungal Solanimycin May Involve an Iterative Nonribosomal Peptide Synthetase Module

Dickeya solani, a plant-pathogenic bacterium, produces solanimycin, a potent hybrid polyketide/nonribosomal peptide (PKS/NRPS) anti-fungal compound. The biosynthetic gene cluster responsible for synthesis of this compound has been identified. Because of instability, the complete structure of the compound has not yet been elucidated, but LC-MS2 identified that the cluster produces two main compounds, solanimycin A and B, differing by a single hydroxyl group. The fragmentation pattern revealed that the central part of solanimycin A is a hexapeptide, Gly-Dha-Dha-Dha-Dha-Dha (where Dha is dehydroalanine). This is supported by isotopic labeling studies using labeled serine and glycine. The N-terminal group is a polyketide-derived C16 acyl group containing a conjugated hexaene, a hydroxyl, and an amino group. The additional hydroxyl group in solanimycin B is on the α-carbon of the glycine residue. The incorporation of five sequential Dha residues is unprecedented because there is only one NRPS module in the cluster that is predicted to activate and attach serine (which is subsequently dehydrated to Dha), meaning that this NRPS module must act iteratively. While a few other iterative NRPS modules are known, they all involve iteration of two or three modules. We believe that the repetitive use of a single module makes the solanimycin biosynthetic pathway unique among NRPSs so far reported.

Poly-L-Lysine to Fight Antibiotic Resistances of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major hospital-associated pathogen that can cause severe infections, most notably in patients with cystic fibrosis (CF) or those hospitalized in intensive care units. Given its remarkable ability to resist antibiotics, P. aeruginosa eradication has grown more challenging. Therefore, there is an urgent need to discover and develop new strategies that can counteract P. aeruginosa-resistant strains. Here, we evaluated the efficacy of poly-L-lysine (pLK) in combination with commonly used antibiotics as an alternative treatment option against P. aeruginosa. First, we demonstrated by scanning electron microscopy that pLK alters the integrity of the surface membrane of P. aeruginosa. We also showed using a fluorometry test that this results in an enhanced permeability of the bacteria membrane. Based on these data, we further evaluated the effect of the combinations of pLK with imipenem, ceftazidime, or aztreonam using the broth microdilution method in vitro. We found synergies in terms of bactericidal effects against either sensitive or resistant P. aeruginosa strains, with a reduction in bacterial growth (up to 5-log₁₀ compared to the control). Similarly, these synergistic and bactericidal effects were confirmed ex vivo using a 3D model of human primary bronchial epithelial cells maintained in an air-liquid interface. In conclusion, pLK could be an innovative antipseudomonal molecule, opening its application as an adjuvant antibiotherapy against drug-resistant P. aeruginosa strains.

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

The naturally occurring homo-polyamide biopolymer, ε-poly-L-lysine (ε-PL) consists of 25-35 L-lysine residues with amide linkages between α-carboxyl groups and ε-amino groups. ɛ-PL exhibits several useful properties because of its unusual structure, such as biodegradability, water solubility, no human toxicity, and broad-spectrum antibacterial activities; it is widely applied in the fields of food, medicine, clinical chemistry and electronics. However, current industrial production of ε-PL is only performed in a few countries. Based on an analysis of the physiological characteristics of ε-PL fermentation, current advances that enhance ε-PL fermentation, from strain improvement to product isolation are systematically reviewed, focusing on: (1) elucidating the metabolic pathway and regulatory mechanism of ε-PL synthesis; (2) enhancing biosynthetic performance through mutagenesis, fermentation optimization and metabolic engineering; and (3) understanding and improving the biological activity and functional properties of ε-PL. Finally, perspectives on engineering and exploiting ε-PL as a source material for the production of various advanced materials are also discussed, providing scientific guidelines for researchers to further improve the ε-PL fermentation process.

A Study of Type II ɛ-PL Degrading Enzyme (pldII) in Streptomyces albulus through the CRISPRi System

ε-Poly-L-lysine (ε-PL) is a widely used antibacterial peptide polymerized of 25–35 L-lysine residues. The antibacterial effect of ε-PL is closely related to the polymerization degree. However, the mechanism of ε-PL degradation in S. albulus remains unclear. This study utilized the integrative plasmid pSET152-based CRISPRi system to transcriptionally repress the ε-PL degrading enzyme (pldII). The expression of pldII is regulated by changing the recognition site of dCas9. Through the ε-PL bacteriostatic experiments of repression strains, it was found that the repression of pldII improves the antibacterial effect of the ε-PL product. The consecutive MALDI-TOF-MS results confirmed that the molecular weight distribution of the ε-PL was changed after repression. The repression strain S1 showed a particular peak with a polymerization degree of 44, and other repression strains also generated ε-PL with a polymerization degree of over 40. Furthermore, the homology modeling and substrate docking of pldII, a typical endo-type metallopeptidase, were performed to resolve the degradation mechanism of ε-PL in S. albulus. The hydrolysis of ε-PL within pldII, initiated from the N-terminus by two amino acid-binding residues, Thr194 and Glu281, led to varying levels of polymerization of ε-PL.

Nonribosomal Peptide Synthesis Definitely Working Out of the Rules

Nonribosomal peptides are microbial secondary metabolites exhibiting a tremendous structural diversity and a broad range of biological activities useful in the medical and agro-ecological fields. They are built up by huge multimodular enzymes called nonribosomal peptide synthetases. These synthetases are organized in modules constituted of adenylation, thiolation, and condensation core domains. As such, each module governs, according to the collinearity rule, the incorporation of a monomer within the growing peptide. The release of the peptide from the assembly chain is finally performed by a terminal core thioesterase domain. Secondary domains with modifying catalytic activities such as epimerization or methylation are sometimes included in the assembly lines as supplementary domains. This assembly line structure is analyzed by bioinformatics tools to predict the sequence and structure of the final peptides according to the sequence of the corresponding synthetases. However, a constantly expanding literature unravels new examples of nonribosomal synthetases exhibiting very rare domains and noncanonical organizations of domains and modules, leading to several amazing strategies developed by microorganisms to synthesize nonribosomal peptides. In this review, through several examples, we aim at highlighting these noncanonical pathways in order for the readers to perceive their complexity.

Synergistic antimicrobial interactions of nisin A with biopolymers and solubilising agents for oral drug delivery

In order to develop bacteriocins, like the lantibiotic nisin A, into effective alternatives to existing antibiotics, their biophysical and physicochemical properties must first be assessed, from solubility, to susceptibility and absorption. It has been well established that formulation strategies at early drug development stages can be crucial for successful outcomes during preclinical and clinical phases of development, particularly for molecules with challenging physicochemical properties. This work elucidates the physicochemical challenges of nisin A in terms of its susceptibility to digestive enzymes like pepsin, pancreatin and proteinase K and its poor solubility at physiological pHs. Low solution concentrations, below the minimum inhibitory concentration against Staphylococcus aureus, were obtained in phosphate buffered saline (PBS, pH 7.4) and in fasted state simulated intestinal fluid (FaSSIF, pH 6.5), while higher solubilities at more acidic pH's such as in a KCl/HCl buffer (pH 2) and in fasted state simulated gastric fluid (FaSSGF, pH 1.6) are observed. Tween® 80 (0.01% v/v) significantly increased the solution concentration of nisin A in PBS (pH 7.4, 24 hr). Pancreatin doubled nisin A's solution concentration at pH 7.4 (PBS) but reduced its' inhibitory activity to ∼ 20%, and pepsin almost completely degraded nisin (after 24 hr), but retained activity at biologically relevant exposure times (∼ 15 min). Harnessing synergism between nisin A and either glycol chitosan or ε-poly lysine, combined with the solubilizing effect of Tween®, increased the antimicrobial activity of nisin A six fold in an in vitro oral administration model.

ε-poly-L-lysine Affects the Vegetative Growth, Pathogenicity and Expression Regulation of Necrotrophic Pathogen Sclerotinia sclerotiorum and Botrytis cinerea

Microbial secondary metabolites produced by Streptomyces are applied to control plant diseases. The metabolite, ε-poly-l-lysine (ε-PL), is a non-toxic food preservative, but the potential application of this compound as a microbial fungicide in agriculture is rarely reported. In this study, the effect and mode of action of ε-PL on two necrotrophic pathogenic fungi, Sclerotinia sclerotiorum and Botrytis cinerea, were investigated. The results showed that ε-PL effectively inhibited the mycelial growth of S. sclerotiorum and B. cinerea with EC₅₀ values of 283 μg/mL and 281 μg/mL, respectively. In addition, ε-PL at the dose of 150 and 300 μg/mL reduced S. sclerotiorum sclerotia formation. The results of the RNA-seq and RT-qPCR validation indicated that ε-PL significantly regulated the gene expression of critical differential expressed genes (DEGs) involved in fungal growth, metabolism, pathogenicity, and induced an increase in the expression of the fungal stress responses and the detoxification genes. These results provided new insights for understanding the modes of action of ε-PL on S. sclerotiorum and B. cinerea and improved the sustainable management of these plant diseases.

Amino acids dominate diffusive nitrogen fluxes across soil depths in acidic tussock tundra

Organic nitrogen (N) is abundant in soils, but early conceptual frameworks considered it nonessential for plant growth. It is now well recognised that plants have the potential to take up organic N. However, it is still unclear whether plants supplement their N requirements by taking up organic N in situ: at what rate is organic N diffusing towards roots and are plants taking it up? We combined microdialysis with live-root uptake experiments to measure amino acid speciation and diffusion rates towards roots of Eriophorum vaginatum. Amino acid diffusion rates (321 ng N cm^-2  h^-1 ) were c. 3× higher than those for inorganic N. Positively charged amino acids made up 68% of the N diffusing through soils compared with neutral and negatively charged amino acids. Live-root uptake experiments confirmed that amino acids are taken up by plants (up to 1 µg N g^-1  min^-1 potential net uptake). Amino acids must be considered when forecasting plant-available N, especially when they dominate the N supply, and when acidity favours proteolysis over net N mineralisation. Determining amino acid production pathways and supply rates will become increasingly important in projecting the extent and consequences of shrub expansion, especially considering the higher C : N ratio of plants relative to soil.

Solution-Blown Poly(hydroxybutyrate) and ε-Poly-l-lysine Submicro- and Microfiber-Based Sustainable Nonwovens with Antimicrobial Activity for Single-Use Applications

Antimicrobial nonwovens for single use applications (e.g., diapers, sanitary napkins, medical gauze, etc.) are of utmost importance as the first line of defense against bacterial infections. However, the utilization of petrochemical nondegradable polymers in such nonwovens creates sustainability-related issues. Here, sustainable poly(hydroxybutyrate) (PHB) and ε-poly-l-lysine (ε-PLL) submicro- and microfiber-based antimicrobial nonwovens produced by a novel industrially scalable process, solution blowing, have been proposed. In such nonwovens, ε-PLL acts as an active material. In particular, it was found that most of ε-PLL is released within the first hour of deployment, as is desirable for the applications of interest. The submicro- and microfiber mat was tested against C. albicans and E. coli, and it was found that ε-PLL-releasing microfibers result in a significant reduction of bacterial colonies. It was also found that ε-PLL-releasing antimicrobial submicro- and microfiber nonwovens are safe for human cells in fibroblast culture. Mechanical characterization of these nonwovens revealed that, even though they are felt as soft and malleable, they possess sufficient strength, which is desirable in the end-user applications.

Characterization of an L-α,β-diaminopropionic acid polymer with comb-like structure isolated from a poly(ε-L-lysine)-producing Streptomyces sp

Polymers of basic amino acids function as polycationic compounds under physiological conditions and exhibit intriguing biological properties, such as antimicrobial and antiviral activities, immunopotentiating ability, and DNA-binding activity. Poly(ε-L-lysine) (ε-PL) produced by some strains of Streptomyces spp. is a cationic homopolymer of L-lysine linking between ε-amino and α-carboxylic acid functional groups and has been used as a food preservative based on its biocompatibility and biodegradability. An ε-PL-producing strain of Streptomyces sp. USE-33 was found to secrete a novel polycationic substance into its culture broth along with ε-PL. High-performance liquid chromatography analyses and one- and two-dimensional ¹H and ¹³C nuclear magnetic resonance (NMR) experiments, accompanied by NMR titration studies, revealed that the secreted substance was poly[β-(L-diaminopropionyl-L-diaminopropionic acid)], PAP, characterized by an isopeptide backbone linking between the β-amino and α-carboxylic acid groups of L-α,β-diaminopropionic acid (L-Dpr) with pendent L-Dpr residues. PAP had a molecular weight of 500 to 1400, and copolymers composed of the two amino acids L-Dpr and L-lysine were not detected in the producer strain USE-33. The strain coproduced high levels of the two poly(amino acid)s in the presence of glycerol, citrate, and ammonium sulfate at pH 4.0 in a two-stage cultivation procedure. PAP exhibited strong inhibitory activities against several yeasts and weaker activities against bacteria than ε-PL. PAP may share a number of biological functions with ε-PL, and the use of PAP along with ε-PL has potential as a specific and advanced material for technical applications in various fields.Key points• Novel cationic poly(amino acid) was found in an ε-PL-producing Streptomyces species.• The l-α,β-diaminopropionic acid polymer was characterized by a comb-like structure.• The novel poly(amino acid), PAP, exhibited antibacterial and antifungal activities.

Packaging of beef fillet with active chitosan film incorporated with ɛ-polylysine: An assessment of quality indices and shelf life

In the current study, the effect on packaged beef fillets (1 × 5 × 8 cm) of using active chitosan film (1%) was investigated. The fillets were stored at 4 °C for 12 days, and the film contained ɛ-polylysine (ɛ-PL) (0.3, 0.6, and 0.9% w/w). Chemical, microbiological, sensory properties, and quality indices of the fillets were investigated. Added to these factors was an assessment of the influence of ɛ-polylysine incorporation on the optical, structural, barrier, and mechanical specifications (elongation at break and tensile strength) of chitosan films. Based on the findings, a significant difference among the corresponding values to thickness, color, water vapor permeability (WVP), and mechanical specifications between the treated films by ɛ-PL and untreated films were noted. In addition, higher values of thickness and tensile strength were correlated with ɛ-PL added active chitosan films while compared with control samples. Additionally, no significant differences regarding the proximate composition (including protein, moisture, and fat) among beef fillet samples were observed. In this regard, due to significantly lower levels of pH, TVB-N, and TBARS ɛ-PL in enriched films, this technique demonstrated some protective effects on beef fillets. Another observation was that lower levels of the total viable count, coliform, mold, yeasts, and higher sensory properties were significantly associated with samples with added ɛ-PL (0.9%). Therefore, adding ɛ-PL into chitosan films could be introduced as an effective technique to extend the shelf life of beef fillets and maintain their quality indices during refrigerated storage.

Polymeric approach to combat drug-resistant methicillin-resistant Staphylococcus aureus

ABSTRACT

The current global death rate has threatened humans due to increase in deadly unknown infections caused by pathogenic microorganisms. On the contrary, the emergence of multidrug-resistant bacteria is also increasing which is leading to elevated lethality rate worldwide. Development of drug-resistant bacteria has become one of the daunting global challenges due to failure in approaching to combat against them. Methicillin-resistant Staphylococcus aureus (MRSA) is one of those drug-resistant bacteria which has led to increase in global mortality rate causing various lethal infections. Polymer synthesis can be one of the significant approaches to combat MRSA by fabricating polymeric coatings to prevent the spread of infections. This review provides last decade information in the development of various polymers against MRSA.

GRAPHICAL ABSTRACT

Layer-by-layer assembled PLGA nanoparticles carrying miR-34a cargo inhibit the proliferation and cell cycle progression of triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) accounts for 15-25% of diagnosed breast cancers, and its lack of a clinically defined therapeutic target has caused patients to suffer from earlier relapse and higher mortality rates than patients with other breast cancer subtypes. MicroRNAs (miRNAs) are small non-coding RNAs that regulate the expression of multiple genes through RNA interference to maintain normal tissue function. The tumor suppressor miR-34a is downregulated in TNBC, and its loss-of-expression correlates with worse disease outcomes. Therefore, delivering miR-34a mimics into TNBC cells is a promising strategy to combat disease progression. To achieve this goal, we synthesized layer-by-layer assembled nanoparticles (LbL NPs) comprised of spherical poly(lactic-co-glycolic acid) cores surrounded by alternating layers of poly-L-lysine (PLL) and miR-34a. TNBC cells internalized these LbL NPs to a greater extent than polyplexes comprised of PLL and miRNA, and confocal microscopy showed that LbL NPs delivered a substantial fraction of miR-34a cargo into the cytosol. This yielded robust suppression of the miR-34a target genes CCND-1, Notch-1, Bcl-2, Survivin, and MDR-1, which reduced TNBC cell proliferation and induced cell cycle arrest. These data validate that miR-34a delivery can impair TNBC cell function and support continued investigation of this platform for treatment of TNBC.

Effects of ε-poly-l-lysine on vegetative growth, pathogenicity and gene expression of Alternaria alternata infecting Nicotiana tabacum

Microbial secondary metabolites produced by Streptomyces are applied to control plant diseases. ε-poly-l-lysine (ε-PL) is a non-toxic food preservative, but the potential application of ε-PL as a microbial fungicide in agriculture has rarely been reported. In this study, Alternaria alternata (A. alternata) was used to reveal the effect and mode of action for ε-PL on the plant pathogenic fungi. The results showed that ε-PL effectively inhibited necrotic-lesion development caused by A. alternata on tobacco. Mycelial growth was also significantly inhibited in vitro by 100 μg/ml ε-PL using in vitro analysis. Moreover, 25 μg/ml ε-PL inhibited spore germination and induced abnormal morphological development of A. alternata hyphae. To clarify the molecular-genetic antifungal mechanisms, we selected several crucial genes involved in the development and pathogenesis of A. alternata and studied their expression regulated by ε-PL. Results of real-time quantitative PCR showed that a mycelium morphology and pathogenic process related cyclic adenosine monophosphate protein (cAMP) dependent protein kinase A (PKA), Alternaria alternata cAMP-dependent protein kinase catalytic subunit (AAPK1) and the early infection-related glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were down-regulated after ε-PL treatment. The results provide novel insights for the application of ε-PL in the control of plant diseases caused by A. alternata.

Effect of ion form of the ion-exchange resin on ε-poly-l-lysine purification from microbial fermentation broth

ε-Poly-l-lysine (ε-PL) is an added-value natural product with widespread application in the fields of food, pharmaceuticals and biopolymer materials. However, the high production cost reduces its application. To improve the efficiency of ε-PL purification for decreasing the cost of downstream processes, the ion form of the ion-exchange resin, which is widely used for ε-PL purification, was investigated systematically in this study. Among eleven cation-exchange resins tested, the Amberlite IRC-50 resin offered the best adsorption capability and the highest desorption ratio. The adsorption kinetics of IRC-50 resin with H⁺, Na⁺ and NH₄ ⁺ ion forms followed a pseudo-second-order model. The dynamic adsorption and desorption parameters of ε-PL were optimized with a column packed with IRC-50 resin with Na⁺ and NH₄ ⁺. It is suggested that NH₄ ⁺ is the optimal ion form of IRC-50 resin for ε-PL extraction. Under optimal conditions, the IRC-50 resin with NH₄ ⁺ achieved the highest ε-PL adsorption capability, purity and recovery ratio of 307.96 mg g^-1, 76.52% and 96.2%, respectively. After further purification, a final ε-PL purity of 97.10% was achieved with a total recovery ratio of 66.01%. This is the first report on improving the ε-PL purification efficiency through optimizing the ion form of the ion-exchange resin. Moreover, it would offer guidance for other natural product recovery processes by ion-exchange chromatography.

Purification and Structural Analysis of the Effective Anti-TMV Compound ε-Poly-l-lysine Produced by Streptomyces ahygroscopicus

Microbial secondary metabolites produced by actinomycetes are important natural products widely applied to control plant diseases. A variety of actinomycetes were isolated from soil samples collected from Tianzhu Mountain in Shenyang, China. A Streptomyces strain Shenyang Tianzhu (STZ) exhibits effective antiviral activity against Tobacco mosaic virus (TMV). The isolate was identified as Streptomyces ahygroscopicus based on its cultural, morphological, physiological, biochemical characteristics as well as the phylogenetic analysis using 16S rRNA sequences. To obtain the pure anti-TMV compound from Streptomyces STZ, the culture broth was subjected to Amberlite IRC-50 ion-exchange resin, SX-8 macroporous adsorption resin and Sephadex G-25 gel column chromatography. The purified active compound was confirmed to be ε-poly-l-lysine (ε-PL), with molecular mass in the range of 3454⁻4352 Da by structural analysis with infrared (IR), matrix-assisted laser desorption ionization-time-of-flight MS (MALDI-TOF), thin-layer chromatography (TLC) and high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR). The protective and curative effects of the purified compound ε-PL were tested and the results showed that the compound exhibited significant protective and curative activity against TMV. The potential application of ε-PL as an efficient anti-plant virus agent was expected.

Efficacy of Various Preservatives on Extending Shelf Life of Vacuum-Packaged Raw Pork during 4°C Storage

Uncontrolled bacterial growth and metabolic activities are responsible for the short shelf life of raw pork. Culture-independent analysis by 16S ribosome cDNA could reveal viable bacteria in raw pork. This study investigated microbial growth and volatile organic compounds of raw pork supplemented with various preservatives. Vacuum-packaged raw pork was stored at 4°C, after soaking in solutions of potassium sorbate, ε-poly-l-lysine, kojic acid (KA), or sodium diacetate, individually. Spoilage of raw pork was monitored by determining pH and total volatile basic nitrogen, whereas bacterial growth was determined by culture-dependent and culture-independent analyses. Data indicated that all the preservatives were able to inhibit bacterial growth and extend the shelf life of pork. High-throughput sequencing of 16S ribosome cDNA indicated that Pseudomonas was inhibited under vacuum conditions, whereas facultative anaerobes ( Acinetobacter, Photobacterium, Brochothrix, and Myroides) were the most active genera in the spoiled pork. Photobacterium was further inhibited by each preservative. The inhibition of Acinetobacter, Photobacterium, and Myroides could be responsible for the extended shelf life of vacuum-packaged pork; they were effectively inhibited by KA, which also induced the longest shelf life. Moreover, 19 types of volatile organic compounds were detected. 3-Methylbutanol, 3-methylbutanol acetate, 2-butanone, toluene, benzeneacetaldehyde, dimethyl trisulfide, and acetoin were associated with spoilage. Furthermore, KA is a potential preservative in raw pork; because no phenol was detectable within 35 days, excessive intake of phenol induced by preservatives was avoided.

NP108, an Antimicrobial Polymer with Activity against Methicillin- and Mupirocin-Resistant Staphylococcus aureus

Staphylococcus aureus is a clinically significant human pathogen that causes infectious diseases ranging from skin and soft tissue infections (SSTI) and health care-associated infections (HAI) to potentially fatal bacteremia and endocarditis. Nasal carriage of S. aureus, especially for persistent carriage, is associated with an increased risk of subsequent infection, particularly nosocomial and surgical site infections (SSI), usually via autoinfection. NP108 is a cationic antimicrobial polymer composed of generally recognized as safe (GRAS) amino acid building blocks. NP108 is broad spectrum and rapidly bactericidal (3-log kill in ≤3 h), killing bacteria by membrane disruption and cell lysis. NP108, contrary to many antibiotics, shows equally effective antimicrobial activity against a variety of S. aureus (MIC₁₀₀ = 8 to 500 mg/liter) and S. epidermidis (MIC₁₀₀ = 4 to 8 mg/liter) isolates, whether exponentially growing or in stationary phase. NP108 is antimicrobially active under nutrient-limiting conditions similar to those found in the anterior nares (MIC₁₀₀ = 8 mg/liter) and kills antibiotic-resilient small colony variants (MIC₁₀₀ = 32 mg/liter) and S. aureus biofilms (prevention, MIC₁₀₀ = 1 to 4 mg/liter; eradication, MIC₁₀₀ ≥ 31.25 mg/liter). NP108 is active against isolates of S. aureus resistant to the current standard-of-care decolonization agent, mupirocin, with no significant increase in the MIC₁₀₀ NP108 is water soluble and has been formulated into compatible aqueous gel vehicles for human use in which antimicrobial efficacy is retained (2.0% [wt/vol]). NP108 is a potential nonantibiotic antimicrobial alternative to antibiotics for the nasal decolonization of S. aureus, with clear advantages in its mechanism of action over the existing gold standard, mupirocin.

Polymeric lipid vesicles with pH-responsive turning on-off membrane for programed delivery of insulin in GI tract

A kind of polymeric lipid vesicles (PLVs) with pH-responsive turning on-off membrane for programed delivery of insulin in gastrointestinal (GI) tract was developed, which was self-assembled from the grafted amphipathic polymer of N-tocopheryl-N'-succinyl-ɛ-poly-l-lysine (TP/SC-g-PLL). By controlling the grafting ratio of hydrophobic alkane and ionizable carboxyl branches, the permeability of membrane was adjustable and thus allowing insulin release in a GI-pH dependent manner. The effects of grafting degree of substitution (DS) on the pH-responsive behavior of the formed vesicles were confirmed by critical aggregation concentration determination, morphology and size characterization. Their transepithelial permeability across the GI tract was proved by both confocal visualization in vitro model of Caco-2 cellular monolayer and in vivo hypoglycemic study in diabetic rats. Accordingly, the work described here indicated that the self-assembled PLVs could be a promising candidate for improving the GI delivery of hydrophilic biomacromolecule agents.

Identification of genetic variations associated with epsilon-poly-lysine biosynthesis in Streptomyces albulus ZPM by genome sequencing

The biosynthesis of the antibiotic epsilon-poly-lysine (ε-PL) in Streptomyces albulus is performed by polylysine synthase (pls); however, the regulatory mechanism of this process is still unknown. Here, we first obtained the complete genome sequence of S. albulus ZPM, which consists of 9,784,577 bp and has a GC content of 72.2%. The genome houses 44 gene clusters for secondary metabolite biosynthesis, in which 20 gene clusters are involved in the biosynthesis of polyketides and nonribosomally synthesized peptides. High-throughput sequencing was further performed, and genetic variants were identified from pooled libraries consisting of the 30 highest-yield mutants or 30 lowest-yield mutants. More than 350 genetic variants associated with ε-PL yield have been identified. One hundred sixty-two affected proteins, from important metabolic enzymes to novel transcriptional regulators, were identified as being related to ε-PL synthesis. HrdD, one of the affected genes, is a sigma factor that shows the most sensitive response to pH change and contains a non-synonymous mutation (A132V) in mutant strains with lower ε-PL yields. Electrophoretic mobility shift assays showed that the pls gene is likely regulated by transcriptional activator HrdD. The data obtained in this study will facilitate future studies on ε-PL yield improvement and industrial bioprocess optimization.

Size and medium conductivity dependence on dielectrophoretic behaviors of gas core poly-L-lysine shell nanoparticles

Dynamic (dis)assembly of biocompatible nanoparticles into 3D, packed structures would benefit drug delivery, films, and diagnostics. Dielectrophoretic (DEP) microdevices can rapidly assemble and manipulate polarizable particles within nonuniform electric fields. DEP has primarily discerned micrometer particles since nanoparticles experience smaller forces. This work examines conductivity and size DEP dependencies of previously unexplored spherical core-shell nanoparticle (CSnp) into 3D particle assemblies. Poly-L-lysine shell material was custom synthesized around a gas core to form CSnps. DEP frequencies from 1 kHz to 80 MHz at fixed 5 volts peak-to-peak and medium conductivities of 10(-5) and 10(-3) S/m were tested. DEP responses of ∼220 and ∼400 nm poly-L-lysine CSnps were quantified via video intensity densitometry at the microdevice's quadrapole electrode center for negative DEP (nDEP) and adjacent to electrodes for positive DEP. Intensity densitometry was then translated into a relative DEP response curve. An unusual nDEP peak occurred at ∼57 MHz with 25-80 times greater apparent nDEP force. All electrical circuit components were then impedance matched, which changed the observed response to weak positive DEP at low frequencies and consistently weak nDEP from ∼100 kHz to 80 MHz. This impedance-matched behavior agrees with conventional Clausius-Mossotti DEP signatures taking into account the gas core's contributions to the polarization mechanisms. This work describes a potential pitfall when conducting DEP at higher frequencies in microdevices and concurrently demonstrates nDEP behavior for a chemically and structurally distinct particle system. This work provides insight into organic shell material properties in nanostructures and strategies to facilitate dynamic nanoparticle assemblies.

Amphiphilic cationic nanogels as brain-targeted carriers for activated nucleoside reverse transcriptase inhibitors

Progress in AIDS treatment shifted emphasis towards limiting adverse effects of antiviral drugs while improving the treatment of hard-to-reach viral reservoirs. Many therapeutic nucleoside reverse transcriptase inhibitors (NRTI) have a limited access to the central nervous system (CNS). Increased NRTI levels induced various complications during the therapy, including neurotoxicity, due to the NRTI toxicity to mitochondria. Here, we describe an innovative design of biodegradable cationic cholesterol-ε-polylysine nanogel carriers for delivery of triphosphorylated NRTIs that demonstrated high anti-HIV activity along with low neurotoxicity, warranting minimal side effects following systemic administration. Efficient CNS targeting was achieved by nanogel modification with brain-specific peptide vectors. Novel dual and triple-drug nanoformulations, analogous to therapeutic NRTI cocktails, displayed equal or higher antiviral activity in HIV-infected macrophages compared to free drugs. Our results suggest potential alternative approach to HIV-1 treatment focused on the effective nanodrug delivery to viral reservoirs in the CNS and reduced neurotoxicity.

The antimicrobial mechanism of action of epsilon-poly-l-lysine

Epsilon-poly-l-lysine (ε-PL) is a natural antimicrobial cationic peptide which is generally regarded as safe (GRAS) as a food preservative. Although its antimicrobial activity is well documented, its mechanism of action is only vaguely described. The aim of this study was to clarify ε-PL's mechanism of action using Escherichia coli and Listeria innocua as model organisms. We examined ε-PL's effect on cell morphology and membrane integrity and used an array of E. coli deletion mutants to study how specific outer membrane components affected the action of ε-PL. We furthermore studied its interaction with lipid bilayers using membrane models. In vitro cell studies indicated that divalent cations and the heptose I and II phosphate groups in the lipopolysaccharide layer of E. coli are critical for ε-PL's binding efficiency. ε-PL removed the lipopolysaccharide layer and affected cell morphology of E. coli, while L. innocua underwent minor morphological changes. Propidium iodide staining showed that ε-PL permeabilized the cytoplasmic membrane in both species, indicating the membrane as the site of attack. We compared the interaction with neutral or negatively charged membrane systems and showed that the interaction with ε-PL relied on negative charges on the membrane. Suspended membrane vesicles were disrupted by ε-PL, and a detergent-like disruption of E. coli membrane was confirmed by atomic force microscopy imaging of supported lipid bilayers. We hypothesize that ε-PL destabilizes membranes in a carpet-like mechanism by interacting with negatively charged phospholipid head groups, which displace divalent cations and enforce a negative curvature folding on membranes that leads to formation of vesicles/micelles.

Poly-L-Lysine compacts DNA, kills bacteria, and improves protease inhibition in cystic fibrosis sputum

RATIONALE

Neutrophil serine proteases in cystic fibrosis (CF) lung secretions partially resist inhibition by natural and exogenous inhibitors, mostly because DNA impairs their control. Cationic polypeptides display the property of condensing DNA and retain antimicrobial properties. We hypothesized that DNA condensation by cationic polypeptides in CF sputum would result in a better control of CF inflammation and infection.

OBJECTIVES

We examined whether poly-L-lysine would compact DNA in CF lung secretions and liquefy CF sputum, improve the control of extracellular proteases by exogenous inhibitors, and whether it displays antibacterial properties toward CF-associated bacteria.

METHODS

We used fluorogenic methods to measure proteolytic activities and inhibition by protease inhibitors in whole sputum homogenates from patients with CF before and after treatment with poly-L-lysine. Antibacterial properties of poly-L-lysine were measured in bacterial cultures and in whole CF sputum. Poly-L-lysine toxicity was evaluated after aerosolization by histologic analysis, flow cytometry, and quantification of proinflammatory cytokines.

MEASUREMENTS AND MAIN RESULTS

Poly-L-lysine compacts CF sputum DNA, generating a liquid phase that improves ciliary beating frequency at the lung epithelial surface, and allows the control of neutrophil elastase and cathepsin G by their natural inhibitors. It retains antimicrobial properties against Pseudomonas aeruginosa and Staphylococcus aureus at doses that induce no inflammation in the mouse lung after aerosol administration.

CONCLUSIONS

Poly-L-lysine may be an alternative to dornase-α to liquefy sputum with added benefits because it helps natural inhibitors to better control the deleterious effects of extracellularly released neutrophil serine proteases and has the ability to kill bacteria in CF sputum.

Draft Genome Sequence of Streptomyces albulus Strain CCRC 11814, an {varepsilon}-Poly-L-Lysine-Producing Actinomycete

Here, we report the draft genome sequence of Streptomyces albulus strain CCRC 11814, a soil-dwelling, Gram-positive bacterium. S. albulus produces ε-poly-l-lysine, which has diverse antimicrobial activity. The genome is 9.43 Mb in size, with a G+C content of 72.2%, and contains 9,177 protein-coding sequences.

Investigation of alginate-ε-poly-L-lysine microcapsules for cell microencapsulation

Cell microencapsulation is a promising approach for cell implantation, cell-based gene therapy, and large-scale cell culture. The well-studied α-AP (alginate-α-poly-L-lysine) microcapsules have been restricted to large-scale cell-culture and clinical applications because of high costs and cytotoxic effects in some cases. This study used ε-poly-L-lysine (ε-PLL), a high-biocompatible and low-cost food additives produced by fermentation, to prepare ε-AP (alginate-ε-PLL) microcapsules with various thickness membranes and swelling behaviors. ε-AP microcapsules were permeable to BSA, a standard protein of culture medium. ε-AP-microencapsulated Chinese hamster ovary (CHO) cells proliferated with culture time; no obvious difference with α-AP-microencapsulated CHO cells during the early 19 days. Whereas ε-AP-microencapsulated CHO cells kept higher viability (OD = 0.646 ± 0.012) on the 22nd day and microcapsule strength (integrity rate of 88%) on the 24th day than that of α-AP microcapsules (OD = 0.558 ± 0.025, integrity rate of 80%). ε-AP (alginate-ε-PLL) microcapsules exhibited more superior properties and could lower the costs to broaden the applications of microencapsulation technology.