Poly-γ-glutamic acid: production, properties and applications

Cell-penetrating activity of a short-chain ε-poly-l-α-lysine

Bacteria produce polycationic homopoly(amino acid)s, which are characterized by isopeptide backbones. We previously demonstrated that two representative bacterial polycationic isopeptides, ε-poly-l-α-lysine consisting of 25-35 l-α-lysine residues (ε-PαL25-35) and ε-poly-l-β-lysine consisting of l-β-lysine residues (ε-PβL4-13), were internalized into mammalian cells by both energy-independent direct penetration and energy-dependent endocytosis/macropinocytosis, and then diffused throughout the cytosol. In this study, we investigated the cell-penetrating activity of an ε-PαL short-chain derivative consisting of 5-14 l-α-lysine residues (ε-PαL5-14) to gain insight into the relationship between the isopeptide-chain length and the manner of cellular internalization. We prepared a conjugate of ε-PαL5-14 and a fluorescent dye (FAM) by click chemistry, and incubated the resulting polymer, ε-PαL5-14-FAM, with HeLa cells. Unlike ε-PαL25-35-FAM, ε-PαL5-14-FAM was internalized into cells only by energy-dependent endocytosis/macropinocytosis. Furthermore, a high concentration (>50 μM) was required for the internalization events. ε-PαL5-14 has a chain length almost equal to that of the membrane permeable ε-PβL4-13, which can enter cells at low concentrations. Considering that the basicity of the β-amino group is higher than that of α-amino acid at physiological pH, ε-PβL is expected to have a greater cell-penetrating capacity than ε-PαL, provided their isopeptide-chain lengths are similar, suggesting that a more extended chain derivative of ε-PβL would be more advantageous for cellular internalization of cargo proteins than ε-PαL25-35.

Chitosan/poly-γ-glutamic acid crosslinked hydrogels: Characterization and application as bio-glues

Ecofriendly hydrogels were prepared using chitosan (CH, 285 kDa) and two fractions of low molecular weight microbial poly-γ-glutamic acid (γ-PGA) (R1 and R2 of 59 kDa and 20 kDa, respectively). The hydrogels were synthesized through sustainable physical blending, employing three CH/γ-PGA mass ratios (1/9, 2/8, and 3/7), resulting in the formation of physically crosslinked materials. The six resulting CH/R1 and CH/R2 hydrogels were physico-chemically characterized and the ones with the highest yields (CH/R1 and CH/R2 ratio of 3/7), analyzed for rheological and morphological properties, showed to act as bio-glues on wood and aluminum compared to commercial vinyl- (V1) and acetovinyl (V2) glues. Lap shear analyses of CH/R1 and CH/R2 blends exhibited adhesive strength on wood, as well as adhesive/cohesive failure like that of V1 and V2. Conversely, CH/R2 had higher adhesive strength and adhesive/cohesive failure on aluminum, while CH/R1 showed an adhesion strength with adhesive failure on the metal similar to that of V1 and V2. Scanning electron microscopy revealed the formation of strong physical bonds between the hydrogels and both substrates. Beyond their use as bio-adhesives, the unique properties of the resulting crosslinked materials make them potentially suitable for various applications in paint, coatings, heritage preservation, and medical sector.

Heterologous synthesis of poly-γ-glutamic acid enhanced drought resistance in maize (Zea mays L.)

Drought stress is the main factor restricting maize yield. Poly-γ-glutamic acid (γ-PGA), as a water-retaining agent and fertilizer synergist, could significantly improve the drought resistance and yield of many crops. However, its high production costs and unclear long-term impact on soil ecology limit its large-scale application. In this study, an environmentally friendly green material γ-PGA was heterologous synthesized in maize for the first time using the synthetic biology method. The genes (PgsA, PgsB, PgsC) participated in γ-PGA synthesis were cloned from Bacillus licheniformis and transformed into maize to produce γ-PGA for the first time. Under drought stress, transgenic maize significantly increased the ear length, ear weight and grain weight by 50 % compared to the control, whereas the yield characteristic of ear weight, grain number per ear, grain weight per ear and 100-grain weight increased by 1.67 %-2.33 %, 3.78 %-13.06 %, 8.41 %-22.06 %, 6.03 %-19.28 %, and 11.85 %-18.36 %, respectively under normal growth conditions. γ-PGA was mainly expressed in the mesophyll cells of maize leaf rosette structure and improved drought resistance and yield by protecting and increasing the expression of genes for the photosynthetic and carbon fixation. This study is an important exploration for maize drought stress molecular breeding and building resource-saving agriculture.

Poly-γ-glutamic acid overproduction of Bacillus licheniformis ATCC 9945a by developing a novel optimum culture medium and glutamate pulse feeding using different experimental design approaches

The commercial production of multifunctional, biocompatible, and biodegradable biopolymers such as poly-γ-glutamic acid via microbial fermentation requires the development of simple and cheap methods for mass production. This study optimized the poly-γ-glutamic acid production of Bacillus licheniformis ATCC 9945a in several steps. At first, the most critical components of the culture medium, including l-glutamic acid, citric acid, and glycerol, were selected by screening nine factors through the Plackett-Burman experimental design and then were optimized using the response surface method and the central composite design algorithm. Under optimal conditions, the production of poly-γ-glutamic acid increased by more than 4.2 times from 11.2 to 47.2 g/L. This is one of the highest production rates of this strain in submerged batch fermentation reported so far using the optimized medium compared to the conventional base medium. A novel and efficient sudden pulse feeding strategy (achieved by a novel one-factorial statistical technique) of l-glutamic acid to the optimized medium increased biopolymer production from 47.2 to 66.1 g/L, the highest value reported in published literature with this strain. This simple, reproducible, and cheap fermentation process can considerably enhance the commercial applications of the poly-γ-glutamic acid synthesized by B. licheniformis ATCC 9945a.

Advances of biological macromolecules hemostatic materials: A review

Achieving hemostasis is a necessary intervention to rapidly and effectively control bleeding. Conventional hemostatic materials currently used in clinical practice may aggravate the damage at the bleeding site due to factors such as poor adhesion and poor adaptation. Compared to most traditional hemostatic materials, polymer-based hemostatic materials have better biocompatibility and offer several advantages. They provide a more effective method of stopping bleeding and avoiding additional damage to the body in case of excessive blood loss. Various hemostatic materials with greater functionality have been developed in recent years for different organs using diverse design strategies. This article reviews the latest advances in the development of polymeric hemostatic materials. We introduce the coagulation cascade reaction after bleeding and then discuss the hemostatic mechanisms and advantages and disadvantages of various polymer materials, including natural, synthetic, and composite polymer hemostatic materials. We further focus on the design strategies, properties, and characterization of hemostatic materials, along with their applications in different organs. Finally, challenges and prospects for the application of hemostatic polymeric materials are summarized and discussed. We believe that this review can provide a reference for related research on hemostatic materials, contributing to the further development of polymer hemostatic materials.

High-level production of poly-γ-glutamic acid by a newly isolated Bacillus sp. YJY-8 and potential use in increasing the production of tomato

Strain YJY-8, a new γ-polyglutamic acid producer, was separated from fermented soybean paste samples. The strain was identified as a genus of Bacillus by morphological and 16S rDNA sequence analysis and was named Bacillus sp. YJY-8. The optimal medium composition and cultural conditions were studied using a single-factor experiment and a response surface experiment. The optimized medium consisted of monosodium glutamate 70 g/L, glucose 54.3 g/L, glycerol 31.8 g/L, ammonium sulfate 11.1 g/L, yeast extract 3.2 g/L, tryptone 1.5 g/L, L-glutamic acid 6.8 g/L, MgSO4 7H2O 0.5 g/L, FeCl3 6H2O 0.02 g/L, KH2PO4 0.9 g/L, CaCl2 0.03 g/L, MnSO4 H2O 0.3 g/L, ammonium molybdate 0.02 g/L, pH 7.0. The optimal cultivation conditions were 35 °C and pH 7.0. Under the optimized conditions, after 48 hr of cultivation, the highest shaking flask fermentation level of γ-PGA reached 65.2 ± 0.36 g/L. In addition, through fed-batch fermentation in 30 L fermenters, the fermentation level of γ-PGA reached its highest level at 88.42 g/L and productivity was 1.23 g/(L hr) after 72 hr. Then, the effect of γ-PGA on tomato yield was investigated. At the seedling stage, the plant height and stem diameter of γ-PGA treated plants increased by 5.69 and 15.735% after spraying γ-PGA for 19 days. During the flowering and fruiting period, the stem diameter of the γ-PGA treatment group increased by 6.74%, with a maximum increase of 11.65%. The number of fruit branches increased by 0.56-16.29% and the number of fruit sets increased by 1.01-28.47%. At the fruit maturation stage, the yield of tomatoes increased by 10.51, 14.27, and 5.83%.

Fabrication of yeast β-glucan/sodium alginate/γ-polyglutamic acid composite particles for hemostasis and wound healing

Particles with a porous structure can lead to quick hemostasis and provide a good matrix for cell proliferation during wound healing. Recently, many particle-based wound healing materials have been clinically applied. However, these products show good hemostatic ability but with poor wound healing ability. To solve this problem, this study fabricated APGG composite particles using yeast β-glucan (obtained from Saccharomyces cerevisiae), sodium alginate, and γ-polyglutamic acid as the starting materials. The structure of yeast β-glucan was modified with many carboxymethyl groups to obtain carboxymethylated β-glucan, which could coordinate with Ca2+ ions to form a crosslinked structure. A morphology study indicated that the APGG particles showed an irregular spheroidal structure with a low density (<0.1 g cm-3) and high porosity (>40%). An in vitro study revealed that the particles exhibited a low BCI value, low hemolysis ratio, and good cytocompatibility against L929 cells. The APGG particles could quickly stop bleeding in a mouse liver injury model and exhibited better hemostatic ability than the commercially available product Celox. Furthermore, the APGG particles could accelerate the healing of non-infected wounds, and the expression levels of CD31, α-SMA, and VEGF related to angiogenesis were significantly enhanced.

Chitin: A versatile biopolymer-based functional therapy for cartilage regeneration

Chitin is the second most abundant biopolymer and its inherent biological characteristics make it ideal to use for tissue engineering. For many decades, its properties like non-toxicity, abundant availability, ease of modification, biodegradability, biocompatibility, and anti-microbial activity have made chitin an ideal biopolymer for drug delivery. Research studies have also shown many potential benefits of chitin in the formulation of functional therapy for cartilage regeneration. Chitin and its derivatives can be processed into 2D/3D scaffolds, hydrogels, films, exosomes, and nano-fibers, which make it a versatile and functional biopolymer in tissue engineering. Chitin is a biomimetic polymer that provides targeted delivery of mesenchymal stem cells, especially of chondrocytes at the injected donor sites to accelerate regeneration by enhancing cell proliferation and differentiation. Due to this property, chitin is considered an interesting polymer that has a high potential to provide targeted therapy in the regeneration of cartilage. Our paper presents an overview of the method of extraction, structure, properties, and functional role of this versatile biopolymer in tissue engineering, especially cartilage regeneration.

Cucumber (Cucumis sativus L.) with heterologous poly-γ-glutamic acid has skin moisturizing, whitening and anti-wrinkle effects

Three genes involved in poly-γ-glutamic acid(γ-PGA)synthesis cloned from Bacillus licheniformis were transformed into cucumber for the first time. Compared with control, its water content increased by 6-14 % and water loss rate decreased by 11-12 %. In zebrafish and human skin experiments, the moisturizing effect of transgenic cucumber was significantly higher than that of CK, γ-PGA and hyaluronic acid group. Transgenic cucumber reduced facial wrinkles and roughness by 19.58 % and 24.97 %, reduced skin melanin content by 5.27 %, increased skin topological angle and L-value by 5.89 % and 2.49 %, and increased the R2 and Q1 values of facial elasticity by 7.67 % and 5.64 %, respectively. The expressions of aqp3, Tyr, silv and OCA2 were down-regulated, eln1, eln2, col1a1a and col1a1b were up-regulated in zebrafish after treated with transgenic cucumber. This study provides an important reference for the endogenous synthesis of important skin care functional molecules in plants.

Culture-dependent and -independent analyses of bacterial compositions and its contributions to formation of γ-aminobutyric acid and poly-γ-glutamic acid in Cheonggukjang

This study was performed to unveil bacterial compositions and their contributions to the formation of γ-aminobutyric acid (GABA) and poly-γ-glutamic acid (γ-PGA) in Cheonggukjang. To predict possible key factors contributing to the content of the bioactive compounds in Cheonggukjang, commercial products were analyzed for various parameters. The content of GABA and γ-PGA showed a negative (R2 = 0.61 - 0.73) and positive correlation (R2 = 0.53 - 0.96) with antioxidative activity. Consistently, GABA content showed a moderate negative correlation with γ-PGA content (R2 = 0.58). Among the physicochemical and microbial parameters, only salinity showed a moderate negative correlation with γ-PGA content (R2 = 0.75), which might be due to the inhibition of bacterial growth. It was also suggested that multiple factors (including bacterial species) were involved in the formation of GABA and γ-PGA in Cheonggukjang. To reveal dominant bacterial species and further presume their contributions to the bioactive compound formation in Cheonggukjang, both culture-independent (metagenomic) and -dependent (culturomic) methods were used. Culture-independent method showed that Bacillus piscis was dominant (23.37 - 94.89 %), followed by B. hisashii (0.00 - 62.45 %) and B. coagulans (0.00 - 13.82 %). Considering the quantitative speciation data on the bioactive compound content in Cheonggukjang (and bacterial production capability) together, it was further elucidated that B. piscis contributed primarily to the bioactive compound formation. Unlike this, culture-dependent analysis revealed that B. licheniformis and B. subtilis were dominant (30.0 - 47.6 and 17.5 - 39.5 %, respectively). Based on the quantitative speciation data on the bacterial production capability of GABA and γ-PGA, B. subtilis was the primarily contributing bacterial species to the bioactive compound formation. Consequently, it was observed that the bacterial compositions and their contributions to the bioactive compound formation determined by the two methods differed considerably, i.e., B. piscis and B. subtilis were identified to be prominent bacterial contributors, respectively, depending on the method used.

Effective Removal of Different Heavy Metals Ion (Cu, Pb, and Cd) from Aqueous Solutions by Various Molecular Weight and Salt Types of Poly-γ-Glutamic Acid

In light of industrial developments, water pollution by heavy metals as hazardous chemicals has garnered attention. Addressing the urgent need for efficient heavy metal removal from aqueous environments, this study delves into using poly-γ-glutamic acid (γ-PGA) for the bioflocculation of heavy metals. Utilizing γ-PGA variants from Bacillus subtilis with different molecular weights and salt forms (Na-bonded and Ca-bonded), the research evaluates their adsorption capacities for copper (Cu), lead (Pb), and cadmium (Cd) ions. It was found that Na-bonded γ-PGA with a high molecular weight showed the highest heavy metal adsorption (92.2-98.3%), particularly at a 0.5% concentration which exhibited the highest adsorption efficiency. Additionally, the study investigated the interaction of γ-PGA in mixed heavy metal environments, and it was discovered that Na-γ-PGA-HM at a 0.5% concentration showed a superior adsorption efficiency for Pb ions (85.4%), highlighting its selectivity as a potential effective biosorbent for wastewater treatment. This research not only enlightens the understanding of γ-PGA's role in heavy metal remediation but also underscores its potential as a biodegradable and non-toxic alternative for environmental cleanup. The findings pave the way for further exploration into the mechanisms and kinetics of γ-PGA's adsorption properties.

Charge neutralized poly(β-amino ester) polyplex nanoparticles for delivery of self-amplifying RNA

Therapeutic self-amplifying RNA (saRNA) is a promising approach for disease treatment, as it can be administered in lower doses than messenger RNA (mRNA) to achieve comparable protein production levels. However, saRNA requires an appropriate delivery vehicle to protect it during transit and facilitate its transfection. A widely-adopted approach has been to use polycations to condense these large anionic macromolecules into polyplex nanoparticles, however their high charge density often elicits cytotoxic effects. In this study we postulated that we could improve the potency and tolerability of such delivery vehicles by co-formulating poly(β-amino ester)s saRNA polyplexes with a non-toxic anionic polymer, γ-polyglutamic acid (γ-PGA) to neutralize partially this positive charge. Accordingly, we prepared a poly(β-amino ester) from 1,6-hexanedioldiacrylate (HDDA) and 4-aminobutanol (ABOL) and initially evaluated the physicochemical properties of the binary polyplexes (i.e. formed from polymer and saRNA only). Optimised binary polyplex formulations were then taken forward for preparation of ternary complexes containing pHDDA-ABOL, saRNA and γ-PGA. Our findings demonstrate that γ-PGA integration into polyplexes significantly enhanced transfection efficacy in HEK293T and A431 cells without affecting polyplex size. Notably, γ-PGA incorporation leads to a pronounced reduction in zeta potential, which reduced the toxicity of the ternary complexes in moDC, NIH3T3, and A431 cells. Furthermore, the presence of γ-PGA contributed to colloidal stability, reducing aggregation of the ternary complexes, as evidenced by insignificant changes in polydispersity index (PDI) after freeze-thaw cycles. Overall, these results suggest that incorporating the appropriate ratio of a polyanion such as γ-PGA with polycations in RNA delivery formulations is a promising way to improve the in vitro delivery of saRNA.

Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability

Microbial biopolymers have emerged as promising solutions for environmental pollution-related human health issues. Poly-γ-glutamic acid (γ-PGA), a natural anionic polymeric compound, is composed of highly viscous homo-polyamide of D and L-glutamic acid units. The extracellular water solubility of PGA biopolymer facilitates its complete biodegradation and makes it safe for humans. The unique properties have enabled its applications in healthcare, pharmaceuticals, water treatment, foods, and other domains. It is applied as a thickener, taste-masking agent, stabilizer, texture modifier, moisturizer, bitterness-reducing agent, probiotics cryoprotectant, and protein crystallization agent in food industries. γ-PGA is employed as a biological adhesive, drug carrier, and non-viral vector for safe gene delivery in tissue engineering, pharmaceuticals, and medicine. It is also used as a moisturizer to improve the quality of hair care and skincare cosmetic products. In agriculture, it serves as an ideal stabilizer, environment-friendly fertilizer synergist, plant-growth promoter, metal biosorbent in soil washing, and animal feed additive to reduce body fat and enhance egg-shell strength.

Genotype-specific germination behavior induced by sustainable priming techniques in response to water deprivation stress in rice

Water stress brought about by climate change is among the major global concerns threatening food security. Rice is an important staple food which requires high water resources. Being a semi-aquatic plant, rice is particularly susceptible to drought. The aim of this work was to develop techniques directed to promote rice resilience to water deprivation stress during germination by implementing specific seed priming treatments. Five popular Italian rice varieties were subjected to priming treatments using novel, sustainable solutions, like poly-gamma-glutamic acid (γ-PGA), denatured γ-PGA (dPGA), and iron (Fe) pulsing, alone or in combination. The effect of the developed priming methods was tested under optimal conditions as well as under water deprivation stress imposed by polyethylene glycol (PEG) treatments. The priming efficacy was phenotypically determined in terms of germination behavior by measuring a series of parameters (germinability, germination index, mean germination time, seed vigor index, root and shoot length, germination stress tolerance index). Biochemical analyses were carried out to measure the levels of iron uptake and accumulation of reactive oxygen species (ROS). Integrative data analyses revealed that the rice varieties exhibited a strong genotype- and treatment-specific germination behavior. PEG strongly inhibited germination while most of the priming treatments were able to rescue it in all varieties tested except for Unico, which can be defined as highly stress sensitive. Molecular events (DNA repair, antioxidant response, iron homeostasis) associated with the transition from seed to seedling were monitored in terms of changes in gene expression profiles in two varieties sensitive to water deprivation stress with different responses to priming. The investigated genes appeared to be differentially expressed in a genotype-, priming treatment-, stress- and stage-dependent manner. The proposed seed priming treatments can be envisioned as sustainable and versatile agricultural practices that could help in addressing the impact of climate challenges on the agri-food system.

Minced Beef Meat Paste Characteristics: Gel Properties, Water Distribution, and Microstructures Regulated by Medium Molecular Mass of γ-Poly-Glutamic Acid

The influences of various m-γ-PGA (0.08-0.20%, w/w) concentrations on the properties of minced beef meat paste in terms of rheological properties, texture, moisture distribution, and microstructures were evaluated. The results indicated that m-γ-PGA enhanced the water-holding capacity, gel strength, texture, and whiteness of the minced beef meat paste. Based on the microstructural results, m-γ-PGA helped form a more organized and compact gel, thereby limiting the migration of water through the gel matrix. In contrast to the control group, the water-holding property, gel strength, and whiteness of minced meat paste gels with m-γ-PGA content of 0.12% increased from 75.89%, 584.51 g·cm, and 61.83 to 79.91%, 780.87 g·cm, and 62.54, respectively (p < 0.05), exhibiting the highest water-holding property and gel strength. Thus, m-γ-PGA exhibits great potential for minced meat paste products as a healthy gel water retainer and enhancer in low-fat meat products.

Poly-γ-glutamic acid improved biological nitrogen fixation, water-nitrogen productivity, and nitrate residue in cotton/soybean intercropping

BACKGROUND

Poly-γ-glutamic acid (γ-PGA) can promote crop growth and improve soil properties efficiently. However, the optimal application rate of γ-PGA in legume/non-legume intercropping systems is still unclear. A potted experiment was conducted to investigate the effects of five γ-PGA rates (0%, 0.1%, 0.2%, 0.3%, and 0.4%, represented by CK, P1, P2, P3, and P4, respectively) on biological nitrogen (N) fixation (BNF), water-N productivity, and nitrate distribution in a cotton/soybean intercropping system.

RESULTS

The results showed that the growth indicators (plant height, stem diameter, leaf area index, root dry weight, root length) of cotton and soybean increased first and then decreased with increasing γ-PGA rates, and all growth indicators of cotton and soybean showed peaks in P3 and P2 treatments. The stable 15 N isotope method indicated that γ-PGA promoted the BNF capacity of soybean and soil. In particular, the percentage of N derived from the atmosphere (Ndfa) in soybean reached 61.94% in the P2 treatment. Poly-γ-glutamic acid improved the water-N productivity, and the total N partial factor productivity (NPFP) and water productivity (WP) in P3 treatment increased by 23.80% and 43.86% compared with the CK treatment. The γ-PGA mitigation of potential nitrate residue also decreased first and then increased with increasing γ-PGA rates.

CONCLUSION

Multivariate regression analysis showed that 0.22% of the optimal γ-PGA application rate could obtain a higher yield and water-N productivity in cotton/soybean intercropping system simultaneously. © 2023 Society of Chemical Industry.

Poly-γ-glutamic acid nanoparticles as adjuvant and antigen carrier system for cancer vaccination

Vaccination is an innovative strategy for cancer treatment by leveraging various components of the patients' immunity to boost an anti-tumor immune response. Rationally designed nanoparticles are well suited to maximize cancer vaccination by the inclusion of immune stimulatory adjuvants. Also, nanoparticles might control the pharmacokinetics and destination of the immune potentiating compounds. Poly-γ-glutamic acid (γ-PGA) based nanoparticles (NPs), which have a natural origin, can be easily taken up by dendritic cells (DCs), which leads to the secretion of cytokines which ameliorates the stimulation capacity of T cells. The intrinsic adjuvant properties and antigen carrier properties of γ-PGA NPs have been the focus of recent investigations as they can modulate the tumor microenvironment, can contribute to systemic anti-tumor immunity and subsequently inhibit tumor growth. This review provides a comprehensive overview on the potential of γ-PGA NPs as antigen carriers and/or adjuvants for anti-cancer vaccination.

Advanced strategies for metabolic engineering of Bacillus to produce extracellular polymeric substances

Extracellular polymeric substances are mainly synthesized via a variety of biosynthetic pathways in bacteria. Bacilli-sourced extracellular polymeric substances, such as exopolysaccharides (EPS) and poly-γ-glutamic acid (γ-PGA), can serve as active ingredients and hydrogels, and have other important industrial applications. However, the functional diversity and widespread applications of these extracellular polymeric substances, are hampered by their low yields and high costs. Biosynthesis of extracellular polymeric substances is very complex in Bacillus, and there is no detailed elucidation of the reactions and regulations among various metabolic pathways. Therefore, a better understanding of the metabolic mechanisms is required to broaden the functions and increase the yield of extracellular polymeric substances. This review systematically summarizes the biosynthesis and metabolic mechanisms of extracellular polymeric substances in Bacillus, providing an in-depth understanding of the relationships between EPS and γ-PGA synthesis. This review provides a better clarification of Bacillus metabolic mechanisms during extracellular polymeric substance secretion and thus benefits their application and commercialization.

Colon-targeted EMSCs conditional medium hydrogel for treatment of ulcerative colitis in mice

Oral ecto-mesenchymal stem cells-conditional medium (EMSCs-CM) is a promising strategy for treating ulcerative colitis (UC). However, this therapy is currently limited by the harsh gastrointestinal environment and poor colonic targeting ability. Herein, a glutamine transaminase 2 (TG2) crosslinked EMSCs-CM hydrogel (EMSCs-CM-Gel) was fabricated by combining EMSCs-CM with negatively chargedγ-polyglutamic acid (γ-PGA) hydrogel. Intestinal epithelial cell 6 (IEC-6) was applied to construct a cell model with lipopolysaccharide to evaluate the anti-inflammatory potential of EMSCs-CMin vitro. The crosslinked gel was orally administered to mice in liquid form to access the effects of EMSCs-CM-Gelin vivo. This study was based on the fact that the hydrogel containing EMSCs-CM has negative charges, which ensure it remains at the positively charged inflamed colon tissue. The EMSCs-CM could continuously be released in the damaged colon mucosa along with the degradation of theγ-PGA hydrogel. Immunofluorescence and western blot were performed to assess the effects of EMSCs-CM-Gel on mice. The resultsin vivoshowed that EMSCs-CM-Gel could significantly suppress the expression of inflammatory cytokines, prevent the shortening of the length of the intestine and repair the intestinal barrier. Collectively, our findings provided a novel colon-targeted strategy, hoping to benefit UC patients a lot.

Biodegradable acids for pyrite depression and green flotation separation - an overview

Exponential increasing demands for base metals have made meaningful processing of their quite low-grade (>1%) resources. Froth flotation is the most important physicochemical pretreatment technique for processing low-grade sulfide ores. In other words, flotation separation can effectively upgrade finely liberated base metal sulfides based on their surface properties. Various sulfide surface characters can be modified by flotation surfactants (collectors, activators, depressants, pH regulators, frothers, etc.). However, these reagents are mostly toxic. Therefore, using biodegradable flotation reagents would be essential for a green transition of ore treatment plants, while flotation circuits deal with massive volumes of water and materials. Pyrite, the most abundant sulfide mineral, is frequently associated with valuable minerals as a troublesome gangue. It causes severe technical and environmental difficulties. Thus, pyrite should be removed early in the beneficiation process to minimize its problematic issues. Recently, conventional inorganic pyrite depressants (such as cyanide, lime, and sulfur-oxy compounds) have been successfully assisted or even replaced with eco-friendly and green reagents (including polysaccharide-based substances and biodegradable acids). Yet, no comprehensive review is specified on the biodegradable acid depression reagents (such as tannic, lactic, humic acids, etc.) for pyrite removal through flotation separation. This study has comprehensively reviewed the previously conducted investigations in this area and provides suggestions for future assessments and developments. This robust review has systematically explored depression performance, various adsorption mechanisms, and aspects of these reagents on pyrite surfaces. Furthermore, factors affecting their efficiency were analyzed, and gaps within each area were highlighted.

The Antimicrobial Effects of Colistin Encapsulated in Chelating Complex Micelles for the Treatment of Multi-Drug-Resistant Gram-Negative Bacteria: A Pharmacokinetic Study

Background: Infections caused by multi-drug-resistant Gram-negative bacteria (MDR-GNB) are an emerging problem globally. Colistin is the last-sort antibiotic for MDR-GNB, but its toxicity limits its clinical use. We aimed to test the efficacy of colistin-loaded micelles (CCM-CL) against drug-resistant Pseudomonas aeruginosa and compare their safety with that of free colistin in vitro and in vivo. Materials and methods: We incorporated colistin into chelating complex micelles (CCMs), thus producing colistin-loaded micelles (CCM-CL), and conducted both safety and efficacy surveys to elucidate their potential uses. Results: In a murine model, the safe dose of CCM-CL was 62.5%, which is much better than that achieved after the intravenous bolus injection of 'free' colistin. With a slow drug infusion, the safe dose of CCM-CL reached 16 mg/kg, which is double the free colistin, 8 mg/kg. The area under the curve (AUC) levels for CCM-CL were 4.09- and 4.95-fold higher than those for free colistin in terms of AUC0-t and AUC0-inf, respectively. The elimination half-lives of CCM-CL and free colistin groups were 12.46 and 102.23 min, respectively. In the neutropenic mice model with carbapenem-resistant Pseudomonas aeruginosa pneumonia, the 14-day survival rate of the mice treated with CCM-CL was 80%, which was significantly higher than the 30% in the free colistin group (p < 0.05). Conclusions: Our results showed that CCM-CL, an encapsulated form of colistin, is safe and effective, and thus may become a drug of choice against MDR-GNB.

Hydrophobic Modification of Poly(γ-glutamic acid) by Grafting 4-Phenyl-butyl Side Groups for the Encapsulation and Release of Doxorubicin

The delivery of drugs is a great challenge, since most of active pharmaceutical ingredients developed today are hydrophobic and poorly water soluble. From this perspective, drug encapsulation on biodegradable and biocompatible polymers can surpass this problem. Poly(γ-glutamic acid) (PGGA), a bioedible and biocompatible polymer has been chosen for this purpose. Carboxylic side groups of PGGA have been partially esterified with 4-phenyl-butyl bromide, producing a series of aliphatic-aromatic ester derivatives with different hydrophilic-lipophilic balances. Using nanoprecipitation or emulsion/evaporation methods, these copolymers were self-assembled in a water solution, forming nanoparticles with average diameters between 89 and 374 nm and zeta potential values between -13.1 and -49.5 mV. The hydrophobic core containing 4-phenyl-butyl side groups was used for the encapsulation of an anticancer drug, such as Doxorubicin (DOX). The highest encapsulation efficiency was reached for a copolymer derived from PGGA, with a 46 mol% degree of esterification. Drug release studies carried out for 5 days at different pHs (4.2 and 7.4) indicated that DOX was released faster at pH 4.2, revealing the potential of these nanoparticles as chemotherapy agents.

Preparation, function, and safety evaluation of a novel degradable dermal filler, the cross-linked poly-γ-glutamic acid hydrogel particles

Poly-γ-glutamic acid (PGA) is a naturally degradable hydrophilic linear microbial polymer with moisturizing, immunogenic, cross-linking, and hydrogel water absorption properties similar to hyaluronic acid, a biomaterial that is commonly used as a dermal filler. To explore the development feasibility of cross-linked PGA as a novel dermal filler, we studied the local skin response to PGA fillers and the effect of various cross-linking preparations on the average longevity of dermal injection. Injection site inflammation and the formation of collagen and elastin were also determined. PGA hydrogel particles prepared using 28% PGA and 10% 1,4-butanediol diglycidyl ether showed optimal filler properties, resistance to moist heat sterilization, and an average filling longevity of 94.7 ± 61.6 days in the dermis of rabbit ears. Local redness and swelling due to filler injection recovered within 14.2 ± 3.6 days. Local tissue necrosis or systemic allergic reactions were not observed, and local collagen formation was promoted. Preliminary results suggested that dermal injection of cross-linked PGA particles appeared safe and effective, suggesting that cross-linked PGA particles could be developed as a new hydrogel dermal filler.

Cooperative Action of Fulvic Acid and Bacillus paralicheniformis Ferment in Regulating Soil Microbiota and Improving Soil Fertility and Plant Resistance to Bacterial Wilt Disease

Excessive continuous cropping and soil degradation, such as acidification, hardening, fertility decline, and the degradation of microbial community, lead to the epidemic of soilborne diseases and cause great loss in agriculture production. Application of fulvic acid can improve the growth and yield of various crops and effectively suppress soilborne plant diseases. Bacillus paralicheniformis strain 285-3 producing poly-gamma-glutamic acid is used to remove the organic acid that can cause soil acidification and increase the fertilizer effect of fulvic acid and the effect of improving soil quality and inhibiting soilborne disease. In field experiments, the application of fulvic acid and Bacillus paralicheniformis ferment effectively reduced the incidence of bacterial wilt disease and improved soil fertility. Both fulvic acid powder and B. paralicheniformis ferment improved soil microbial diversity and increased the complexity and stability of the microbial network. For B. paralicheniformis ferment, the molecular weight of poly-gamma-glutamic acid became smaller after heating, which could better improve the soil microbial community and network structure. In fulvic acid and B. paralicheniformis ferment-treated soils, the synergistic interaction between microorganisms increased and the number of keystone microorganisms increased, which included antagonistic bacteria and plant growth-promoting bacteria. Changes in the microbial community and network structure were the main reason for the reduced incidence of bacterial wilt disease. Application of fulvic acid and Bacillus paralicheniformis ferment improved soil physicochemical properties and effectively controlled bacterial wilt disease by changing microbial community and network structure and enriching antagonistic and beneficial bacteria. IMPORTANCE Continuous cropping tobacco has led to soil degradation and caused soilborne bacterial wilt disease. Fulvic acid as a biostimulator was applied to restore soil and control bacterial wilt disease. For improving its effect, fulvic acid was fermented with Bacillus paralicheniformis strain 285-3 producing poly-gamma-glutamic acid. Fulvic acid and B. paralicheniformis ferment inhibited bacterial wilt disease, improved soil quality, enriched beneficial bacteria, and increased microbial diversity and microbial network complexity. Some keystone microorganisms in fulvic acid and B. paralicheniformis ferment-treated soils had potential antimicrobial activity and plant growth-promoting attributes. Fulvic acid and B. paralicheniformis 285-3 ferment could be used to restore soil quality and microbiota and control bacterial wilt disease. This study found new biomaterial to control soilborne bacterial disease by combining fulvic acid and poly-gamma-glutamic acid application.

A triple-network carboxymethyl chitosan-based hydrogel for hemostasis of incompressible bleeding on wet wound surfaces

Hydrogel is a kind of hemostatic agent with good application prospect. However, the water molecules on the wound made the hydrogel less adhesive to wet wound tissue. Herein, the carboxymethyl chitosan (CMCS)/oxidized dextran (OD)/γ-polyglutamic acid (γ-PGA) hydrogel was prepared using a double-barreled syringe for hemostasis of diffuse and incompressible wound bleeding. The hydrogel formation was based on the intramolecular lactam bonds, intermolecular amide bonds, and Schiff base bonds. In the hydrogel, the super hydrophilic γ-PGA could drain the surface moisture of the wound and create a local dry environment for enhanced surface adhesion. In vivo study showed that the CMCS/ODex/γ-PGA hydrogel possesses a good biosafety and biodegradability. Interestingly, the CMCS/ODex/γ-PGA hydrogel exhibited excellent hemostatic abilities in dynamic humid environment and resisted a high blood pressure of 238 mmHg, which exceeds the threshold systolic blood pressure of healthy adults (i.e., 120 mmHg). Together with the antibacterial and reactive nitrogen species scavenging activities, this study is expected to provide a new method to design the wet-surface adhesives for the efficient hemostatic application.

Effects of Fe2+ addition to sugarcane molasses on poly-γ-glutamic acid production in Bacillus licheniformis CGMCC NO. 23967

BACKGROUND

Poly-γ-glutamic acid (γ-PGA) is biodegradable, water-soluble, environment-friendly, and edible. Consequently, it has a variety of industrial applications. It is crucial to control production cost and increase output for industrial production γ-PGA.

RESULTS

Here γ-PGA production from sugarcane molasses by Bacillus licheniformis CGMCC NO. 23967 was studied in shake-flasks and bioreactors, the results indicate that the yield of γ-PGA could reach 40.668 g/L in a 5L stirred tank fermenter. Further study found that γ-PGA production reached 70.436 g/L, γ-PGA production and cell growth increased by 73.20% and 55.44%, respectively, after FeSO₄·7H₂O was added. Therefore, we investigated the metabolomic and transcriptomic changes following FeSO₄·7H₂O addition. This addition resulted in increased abundance of intracellular metabolites, including amino acids, organic acids, and key TCA cycle intermediates, as well as upregulation of the glycolysis pathway and TCA cycle.

CONCLUSIONS

These results compare favorably with those obtained from glucose and other forms of biomass feedstock, confirming that sugarcane molasses can be used as an economical substrate without any pretreatment. The addition of FeSO₄·7H₂O to sugarcane molasses may increase the efficiency of γ-PGA production in intracellular.

Bacillaene, sharp objects consist in the arsenal of antibiotics produced by Bacillus

Bacillus species act as plant growth-promoting rhizobacteria (PGPR) that can produce a large number of bioactive metabolites. Bacillaene, a linear polyketide/nonribosomal peptide produced by Bacillus strains, is synthesized by the trans-acyltransferase polyketide synthetase. The complexity of the chemical structure, particularity of biosynthesis, potent bioactivity, and the important role of competition make Bacillus an ideal antibiotic weapon to resist other microbes and maintain the optimal rhizosphere environment. This review provides an updated view of the structural features, biological activity, biosynthetic regulators of biosynthetic pathways, and the important competitive role of bacillaene during Bacillus survival.

Production of polyglutamic acid-like mucilage protein by Peribacillus simplex strain 8h

Polyglutamic acid (PGA), a protein in the mucilage of PGA-producing Bacillus spp., has expected applications in medical and biotechnological industries. Although the Bacillaceae family contains over 100 genera, research on bacterial PGA has exclusively focused on the genus Bacillus, especially B. subtilis var. natto and B. licheniformis. In the present study, indigenous Bacillaceae family strains were isolated from withered leaves and soil samples and screened for PGA production. As a result of the screening, the strain 8h was found to produce a mucilage possessing greater viscosity than PGA of B. subtilis var. natto (natto PGA). Biochemical analyses revealed that the 8h mucilage contains 63% protein and 37% polysaccharide, while mucilage of B. subtilis var. natto is composed of 61% protein and 39% polysaccharide. The most plentiful amino acid in 8h mucilage protein was glutamate (43%, mol/mol), which is similar to that of natto PGA, suggesting that it possesses characteristics of PGA. Although natto mucilage contains fructan, glucan was found as the polysaccharide of 8h mucilage. While phylogenetic studies indicated that the strain 8h belongs to Peribacillus simplex, the yield of the viscous mucilage by strain 8h was significantly higher than P. simplex type strain, suggesting that 8h is a mucilage-overproducing strain of P. simplex. Interestingly, 8h mucilage protein was found to contain more hydrophobic amino acid residues than natto PGA, suggesting that its amphiphilicity is suitable as a drug carrier and adjuvant. The present study is the first report of viscous mucilage and PGA-like protein produced by the genus Peribacillus.

Targeted poly(L-glutamic acid)-based hybrid peptosomes co-loaded with doxorubicin and USPIONs as a theranostic platform for metastatic breast cancer

Peptosomes, as a vesicular polypeptide-based system and a versatile carrier for co-delivery of hydrophilic and hydrophobic materials, provide great delivery opportunities due to the intrinsic biocompatibility and biodegradability of the polypeptides backbone. In the current study, a novel poly(L-glutamic acid)-block-polylactic acid di-block copolymer (PGA-PLA) was synthesized in two steps. Firstly, γ-benzyl L-glutamate-N-carboxy anhydride (BLG-NCA) and 3,6-dimethyl-1,4-dioxane-2,5-dione were polymerized using N-hexylamine and benzyl alcohol as initiators to produce poly(γ-benzyl L-glutamate (PBLG) and polylactic acid. Then, PBLG was deprotected to produce PGA. Secondly, PGA was conjugated to the benzyl-PLGA to fabricate PGA-PLA diblock copolymer. The synthesized diblock copolymer was used for the encapsulation of doxorubicin, as hydrophilic anticancer and ultra-small superparamagnetic iron oxide nanoparticles (USPIONs) as hydrophobic contrast agent within aqueous core and bilayer of vesicular peptosome, respectively via double emulsion method. The prepared peptosomes (Pep@USPIONs-DOX) controlled the release of DOX (<15 % of the encapsulated DOX release up to 240 h of incubation at the physiological conditions) while increasing the stability and solubility of the hydrophobic USPIONs. Then, AS1411 DNA aptamer was decorated on the surface of the PGA-PLA peptosomes (Apt-Pep@USPIONs-DOX). The prepared targeted and non-targeted platforms showed spherical morphology with hydrodynamic sizes of 265 ± 52 and 229 ± 44 nm respectively. In vitro cellular cytotoxicity and cellular uptake were studied in nucleolin positive (4T1) and nucleolin negative (CHO) cell lines. Cellular uptake of the targeted formulation was greater than that of non-targeted peptosome, while cellular internalization of these peptosomes was identical in CHO cells. Moreover, targeted peptosomes showed greater toxicity than non-targeted peptosome in 4T1 cell line. The prepared theranostic targeted peptosomes demonstrated improved capability in terms of survival rate, biodistribution, tumor suppression efficiency, and MR imaging in the 4T1 tumor-bearing mice.

A novel manganese dioxide-based drug delivery strategy via in situ coating γ-polyglutamic acid/cisplatin for intelligent anticancer therapy

Cisplatin (CDDP) is one of the most frequently used chemotherapeutic drugs due to its broad-spectrum and potent antitumor activity. Unfortunately, inactivation due to glutathione (GSH) substances and insufficient cellular uptake of CDDP greatly hinder its clinical applications. Herein, manganese dioxide (MnO₂) was reported as an efficient glutathione (GSH) consumption material for promoting the accumulation and preventing premature leakage of CDDP in tumor cells. In this work, γ-polyglutamic acid/cisplatin (PGA/CDDP) conjugates and PGA/CDDP nanoparticles (NPs) were respectively constructed via the ligand exchange reaction and electrostatic interaction. Furthermore, PGA/CDDP NPs were in situ coated with MnO₂ (PGA/CDDP@MnO₂ NPs) through the redox reaction of the residual carboxyl group (-COOH) and potassium permanganate (KMnO₄). As a result, the PGA/CDDP@MnO₂ NPs achieved a satisfactory drug-loading efficiency (ca. 37.26%) and multi-responsive controlled drug release. Remarkably, the MnO₂ shells exhibited excellent performance for efficient glutathione (GSH) consumption and significantly enhanced the killing effect (ca. 2-3 times) in human lung cancer cells (A549) compared with pure CDDP. Moreover, it was observed that PGA/CDDP@MnO₂ NPs could also inhibit the migration and invasion of A549 cells. Overall, these remarkable performances of PGA/CDDP@MnO₂ NPs make MnO₂ promising for controlled drug release and intelligent anticancer therapy.

Poly-gamma-glutamic acid biopolymer: a sleeping giant with diverse applications and unique opportunities for commercialization

Poly-gamma-glutamic acid (γ-PGA) is a biodegradable, non-toxic, ecofriendly, and non-immunogenic biopolymer. Its phenomenal properties have gained immense attention in the field of regenerative medicine, the food industry, wastewater treatment, and even in 3D printing bio-ink. The γ-PGA has the potential to replace synthetic non-degradable counterparts, but the main obstacle is the high production cost and lower productivity. Extensive research has been carried out to reduce the production cost by using different waste; however, it is unable to match the commercialization needs. This review focuses on the biosynthetic mechanism of γ-PGA, its production using the synthetic medium as well as different wastes by L-glutamic acid-dependent and independent microbial strains. Furthermore, various metabolic engineering strategies and the recovery processes for γ-PGA and their possible applications are discussed. Finally, highlights on the challenges and unique approaches to reduce the production cost and to increase the productivity for commercialization of γ-PGA are also summarized.

Online measurement of the viscosity in shake flasks enables monitoring of γ-PGA production in depolymerase knockout mutants of Bacillus subtilis with the phosphate-starvation inducible promoter Ppst

Poly-γ-glutamic acid (γ-PGA) is a biopolymer with a wide range of applications, mainly produced using Bacillus strains. The formation and concomitant secretion of γ-PGA increases the culture broth viscosity, while enzymatic depolymerisation and degradation of γ-PGA decreases the culture broth viscosity. In this study, the recently published ViMOS (Viscosity Monitoring Online System) is applied for optical online measurements of broth viscosity in eight parallel shake flasks. It is shown that the ViMOS is suitable to monitor γ-PGA production and degradation online in shake flasks. This online monitoring enables the detailed analysis of the P_pst promoter and γ-PGA depolymerase knockout mutants in genetically modified Bacillus subtilis 168. The P_pst promoter becomes active under phosphate starvation. The different single depolymerase knockout mutants are ∆ggt, ∆pgdS, ∆cwlO and a triple knockout mutant. An increase in γ-PGA yield in g_γ-PGA /g_glucose of 190% could be achieved with the triple knockout mutant compared to the P_pst reference strain. The single cwlO knockout also increased γ-PGA production, while the other single knockouts of ggt and pgdS showed no impact. Partial depolymerisation of γ-PGA occurred despite the triple knockout. The online measured data are confirmed with offline measurements. The online viscosity system directly reflects γ-PGA synthesis, γ-PGA depolymerisation, and changes in the molecular weight. Thus, the ViMOS has great potential to rapidly gain detailed and reliable information about new strains and cultivation conditions. The broadened knowledge will facilitate the further optimization of γ-PGA production.

A circular bioprocess application of algal-based substrate for Bacillus subtilis natto production of γ-PGA

Poly-γ-glutamic acid (γ-PGA) is a bio-derived water-soluble, edible, hydrating, non-immunogenic polymer. Bacillus subtilis natto is a wild-type γ-PGA producer originally isolated from Japanese fermented natto beans whose activity has been shown to be enhanced through ion-specific activation of Extrachromosomal DNA maintenance mechanisms. Being a GRAS γ-PGA producer, this microorganism has attracted great interest in its use within an industrial context. Here we successfully synthesised amorphous, crystalline and semi-crystalline γ-PGA between 11-27 g/L. In line with circular economy principles, scalable macroalgal biomass has been evaluated as substrate for γ-PGA, displaying great potential in both yields and material composition. In this study whole cell, freeze dried seaweed -namely Laminaria digitata, Saccharina latissima and Alaria esculenta-were pre-treated by means of mechanical methods, sterilised and subsequently inoculated with B. subtilis natto. High shear mixing was found to be the most suitable pre-treatment technique. Supplemented L. digitata (9.1 g/L), S. latissima (10.2 g/L), A. esculenta (13 g/L) displayed γ-PGA yields comparable to those of standard GS media (14.4 g/L). Greatest yields of pure γ-PGA were obtained during the month of June for L. digitata (Avg. 4.76 g/L) comparable to those obtained with GS media (7.0 g/L). Further, pre-treated S. latissima and L. digitata complex media enabled for high molar mass (4,500 kDa) γ-PGA biosynthesis at 8.6 and 8.7 g/L respectively. Compared to standard GS media, algal derived γ-PGA displayed significantly higher molar masses. Further studies will be necessary to further evaluate the impact of varying ash contents upon the stereochemical properties and modify the properties of algal media based γ-PGA with the aid of key nutrients; however, the material synthesised to date can directly displace a number of fossil fuel derived chemicals in drug delivery applications, cosmetics, bioremediation, wastewater treatment, flocculation and as cryoprotectants.

High Molecular Weight Poly(glutamic acid) to Improve BMP2-Induced Osteogenic Differentiation

FDA-approved bone morphogenetic protein 2 (BMP2) has serious side effects due to the super high dose requirement. Heparin is one of the most well-studied sulfated polymers to stabilize BMP2 and improve its functionality. However, the clinical use of heparin is questionable because of its undesired anticoagulant activity. Recent studies suggest that poly(glutamic acid) (pGlu) has the potential to improve BMP2 bioactivity with less safety concerns; however, the knowledge on pGlu's contribution remains largely unknown. Therefore, we aimed to study the role of pGlu in BMP2-induced osteogenesis and its potential application in bone tissue engineering. Our data, for the first time, indicated that both low (L-pGlu) and high molecular weight pGlu (H-pGlu) were able to significantly improve the BMP2-induced early osteoblastic differentiation marker (ALP) in MC3T3-E1 preosteoblasts. Importantly, the matrix mineralization was more rapidly enhanced by H-pGlu compared to L-pGlu. Additionally, our data indicated that only α-H-pGlu could significantly improve BMP2's activity, whereas γ-H-pGlu failed to do so. Moreover, both gene expression and mineralization data demonstrated that α-H-pGlu enabled a single dose of BMP2 to induce a high level of osteoblastic differentiation without multiple doses of BMP2. To study the potential application of pGlu in tissue engineering, we incorporated the H-pGlu+BMP2 nanocomplexes into the collagen hydrogel with significantly elevated osteoblastic differentiation. Furthermore, H-pGlu-coated 3D porous gelatin and chitosan scaffolds significantly enhanced osteogenic differentiation through enabling sustained release of BMP2. Thus, our findings suggest that H-pGlu is a promising new alternative with great potential for bone tissue engineering applications.

The combined application of γ-PGA-producing bacteria and biochar reduced the content of heavy metals and improved the quality of tomato (Solanum lycopersicum L.)

Plant growth-promoting bacteria and biochar have been widely used as immobilizers to remediate heavy metal contaminated soil. However, few studies have unraveled the effect and synergistic mechanism of combined application of plant growth-promoting bacteria and biochar on in situ heavy metal contaminated soil remediation and plant yield and quality improvement under heavy metal pollution stress. In this study, the effects of biochar, γ-PGA-producing bacteria (Bacillus amyloliquefaciens strain W25) and their combined application on Cd and Pb immobilization, γ-PGA production in soil filtrate, the bacterial community in rhizosphere soil, physicochemical properties of soil, heavy metal uptake, and quality and yield of tomato in heavy metal-contaminated soil were investigated. The application of W25, biochar, and their combinations significantly reduced Cd content in mature tomato fruits by 22-60%, increased the single fruit weight and lycopene content by 7-21% and 23-48%, respectively, and the combination of biochar and W25 had the best effect. All the treatments significantly reduced DTPA-Cd and DTPA-Pb contents in rhizosphere soil (42-53% and 6.5-35%), increased the pH value and the activities of urease-alkaline phosphatase of soil, but did not affect the expression of heavy metal transporter gene LeNRAMP1 in tomato roots. Biochar + W25 increased the relative abundance of plant growth-promoting bacteria such as Bacillus and Streptomyces. Biochar-enhanced plant growth-promoting bacteria to settle and colonize in soil significantly improved the ability of strain W25 to produce γ-PGA, and immobilized Cd in soil filtrate. The combination of biochar and plant growth-promoting bacteria ensures safe crop production in heavy metal-contaminated soil.

Cytokine Therapy Combined with Nanomaterials Participates in Cancer Immunotherapy

Immunotherapy has gradually become an emerging treatment modality for tumors after surgery, radiotherapy, and chemotherapy. Cytokine therapy is a promising treatment for cancer immunotherapy. Currently, there are many preclinical theoretical bases to support this treatment strategy and a variety of cytokines in clinical trials. When cytokines were applied to tumor immunotherapy, it was found that the efficacy was not satisfactory. As research on tumor immunity has deepened, the role of cytokines in the tumor microenvironment has been further explored. Meanwhile, the study of nanomaterials in drug delivery has been fully developed in the past 20 years. Researchers have begun to think about the possibility of combining cytokine therapy with nanomaterials. Herein, we briefly review various nano-delivery systems that can directly deliver cytokines or regulate the expression of cytokines in tumor cells for cancer immunotherapy. We further discussed the feasibility of the combination of various therapies. We looked forward to the main challenges, opportunities, and prospects of tumor immunotherapy with multiple cytokines and a nano-delivery system.

Poly-γ-glutamic acid promoted maize root development by affecting auxin signaling pathway and the abundance and diversity of rhizosphere microbial community

BACKGROUND

The root systems of higher plants play an important role in plant growth and development. In our present study, it was found that poly-γ-glutamic acid (γ-PGA), an environmentally friendly biomacromolecule, significantly improved root development in maize.

RESULTS

After treatment with γ-PGA for 7 days, the fresh weight of maize roots was significantly increased and the differences between γ-PGA treated group and control group were mainly caused by the number (higher by 71.87% compared to the control) and length of lateral roots. RNAseq and RT-PCR analyses showed that γ-PGA treatment upregulated the expression of genes related to the synthesis of auxins and auxin signal in maize roots. In addition, γ-PGA promoted the accumulation of plant growth-promoting bacteria, such as Azospirillum, Azohydromonas, Ramlibacter, and Sphingobium (Proteobacteria), Streptomyces (Actinobacteria), Parasegetibacter (Bacteroidetes), and Gemmatimonas (Gemmatimonadetes) in rhizosphere soil and the secretion of auxins. The results of this study deepened our understanding of the effects and mechanism of γ-PGA on maize root development, and as well as highlighted the possibility of using γ-PGA to improve crop growth and soil environment.

CONCLUSIONS

γ-PGA promotes early growth and development of maize roots by inducing the secretion and accumulation of auxin in roots and in rhizosphere soil, and increasing the abundance of plant growth promoting bacteria.

Comparative transcriptomics reveal different genetic adaptations of biofilm formation in Bacillus subtilis isolate 1JN2 in response to Cd2+ treatment

Biofilm plays important roles in the life cycle of Bacillus species, such as promoting host and object surface colonization and resisting heavy metal stress. This study utilized transcriptomics to evaluate the impacts of cadmium on the components, morphology, and function of biofilms of Bacillus subtilis strain 1JN2. Under cadmium ion stress, the morphology of the B. subtilis 1JN2 biofilm was flattened, and its mobility increased. Moreover, differential gene expression analysis showed that the main regulator of biofilm formation, Spo0A, decreased in expression under cadmium ion stress, thereby inhibiting extracellular polysaccharide synthesis through the SinI/SinR two-component regulatory system and the AbrB pathway. Cadmium ion treatment also increased the SigD content significantly, thereby increasing the expression of the flagella encoding and assembly genes in the strain. This promoted poly-γ-glutamic acid production via the DegS/DegU two-component regulatory system and the conversion of biofilm extracellular polysaccharide to poly-γ-glutamic acid. This conferred cadmium stress tolerance in the strain. Additionally, the cadmium ion-mediated changes in the biofilm composition affected the colonization of the strain on the host plant root surface. Cadmium ions also induced surfactin synthesis. These findings illustrate the potential of Bacillus species as biocontrol strains that can mitigate plant pathogenic infections and heavy metal stress. The results also provide a basis for the screening of multifunctional biocontrol strains.

Construction of a double-responsive modified guar gum nanoparticles and its application in oral insulin administration

The use of intelligent insulin delivery systems has become more important for treating diabetes. In this study, a dual-responsive oral insulin delivery nanocarrier that responds to glucose and pH has been developed. First, the oleic acid hydrophobic modified guar gum (GG) was synthesized by the esterification reaction, and the γ-polyglutamic acid (γ-PGA) was coupled with GG by the amidation reaction. The obtained pH-responsive copolymer (γ-PGA-GG) was cross-linked by concanavalin A to obtain pH/glucose dual-responsive nanocarriers, and insulin was effectively loaded into the dual-responsive nanocarriers. The insulin-loaded nanoparticles can achieve effective pH and glucose responses, releasing insulin on demand. In vitro and in vivo studies demonstrated the dual-responsive nanoparticles can protect insulin against the pH changes in the digestive tract and deliver insulin into the body to exert a hypoglycemic effect. Moreover, the dual-responsive nanoparticles have significant potential to be employed for oral insulin delivery.

Tissue-Engineered Models of the Human Brain: State-of-the-Art Analysis and Challenges

Neurological disorders affect billions of people across the world, making the discovery of effective treatments an important challenge. The evaluation of drug efficacy is further complicated because of the lack of in vitro models able to reproduce the complexity of the human brain structure and functions. Some limitations of 2D preclinical models of the human brain have been overcome by the use of 3D cultures such as cell spheroids, organoids and organs-on-chip. However, one of the most promising approaches for mimicking not only cell structure, but also brain architecture, is currently represented by tissue-engineered brain models. Both conventional (particularly electrospinning and salt leaching) and unconventional (particularly bioprinting) techniques have been exploited, making use of natural polymers or combinations between natural and synthetic polymers. Moreover, the use of induced pluripotent stem cells (iPSCs) has allowed the co-culture of different human brain cells (neurons, astrocytes, oligodendrocytes, microglia), helping towards approaching the central nervous system complexity. In this review article, we explain the importance of in vitro brain modeling, and present the main in vitro brain models developed to date, with a special focus on the most recent advancements in tissue-engineered brain models making use of iPSCs. Finally, we critically discuss achievements, main challenges and future perspectives.

Structural and genetic insights into a poly-γ-glutamic acid with in vitro antioxidant activity of Bacillus velezensis VCN56

Poly-γ‑glutamic acid (γ‑PGA) produced by Bacillus species is a natural biopolymer, which is widely used in various fields including food, pharmaceuticals, and cosmetics. In this study, the screening of 19 Bacillus isolates derived from traditionally fermented foods revealed that Bacillus velezensis VCN56 was the most potent γ‑PGA producer. The maximum concentration of crude γ‑PGA was 32.9 ± 1.5 g/L in the PGA-3 medium containing glycerol, citric acid, sodium glutamate, NH₄Cl, and starch. The resulting γ-PGA was purified and then characterized by HPLC, FTIR, and ¹H-NMR analyses. Molecular weight of purified γ‑PGA was estimated to be 98 kDa with a polydisperse index of 2.04. Notably, the pure γ‑PGA showed significant in vitro antioxidant scavenging activities against 1,1-diphenyl-2-picrylhydrazyl (72.0 ± 1.5%), hydroxyl (81.0 ± 0.6%), and superoxide (43.9 ± 0.8%) radicals at the concentration of 4 mg/mL. Using whole-genome sequencing, the genetic organization of pgs operon responsible for γ‑PGA biosynthesis in B. velezensis VCN56 differs from those in other Bacillus genomes. Further genome analysis revealed metabolic pathways for γ-PGA production and degradation. For the first time, the present study provides a better understanding of γ-PGA with a promising antioxidant activity produced by B. velezensis at the phenotypic, biochemical, and genomic levels, which hold potential applications in the foods, cosmetics, and pharmaceutical industries.

Preparation of gamma poly-glutamic acid/hydroxyapatite/collagen composite as the 3D-printing scaffold for bone tissue engineering

Background

All types of movements involve the role of articular cartilage and bones. The presence of cartilage enables bones to move over one another smoothly. However, repetitive microtrauma and ischemia as well as genetic effects can cause an osteochondral lesion. Numerous treatment methods such as microfracture surgergy, autograft, and allograft, have been used, however, it possesses treatment challenges including prolonged recovery time after surgery and poses a financial burden on patients. Nowadays, various tissue engineering approaches have been developed to repair bone and osteochondral defects using biomaterial implants to induce the regeneration of stem cells. 

Methods

In this study, a collagen (Col)/γ-polyglutamate acid (PGA)/hydroxyapatite (HA) composite scaffold was fabricated using a 3D printing technique. A Col/γ-PGA/HA 2D membrane was also fabricated for comparison. The scaffolds (four layers) were designed with the size of 8 mm in diameter and 1.2 mm in thickness. The first layer was HA/γ-PGA and the second to fourth layers were Col/γ-PGA. In addition, a 2D membrane was constructed from hydroxyapatite/γ-PGA and collagen/γ-PGA with a ratio of 1:3. The biocompatibility property and degradation activity were investigated for both scaffold and membrane samples. Rat bone marrow mesenchymal stem cells (rBMSCs) and human adipose-derived stem cells (hADSCs) were cultured on the samples and were tested in-vitro to evaluate cell attachment, proliferation, and differentiation. In-vivo experiments were performed in the rat and nude mice models.

Results

In-vitro and in-vivo results show that the developed scaffold is of well biodegradation and biocompatible properties, and the Col-HA scaffold enhances the mechanical properties for osteochondrogenesis in both in-vitro and animal trials.

Conclusions

The composite would be a great biomaterial application for bone and osteochondral regeneration.

Poly-Gamma-Glutamic Acid Secretion Protects Bacillus subtilis from Zinc and Copper Intoxication

Zinc and copper are essential micronutrients that serve as a cofactors for numerous enzymes. However, when present at elevated concentrations, zinc and copper are highly toxic to bacteria. To combat the effects of zinc and copper excess, bacteria have evolved a wide array of defense mechanisms. Here, we show that the Gram-positive soil bacterium, Bacillus subtilis, produces the extracellular polymeric substance, poly-gamma-glutamate (γ-PGA) as a protective mechanism in response to zinc and copper excess. Furthermore, we provide evidence that zinc and copper dependent γ-PGA production is independent of the DegS-DegQ two-component regulatory system and likely occurs at a posttranscriptional level through the small protein, PgsE. These data provide new insight into bacterial metal resistance mechanisms and contribute to our understanding of the regulation of bacterial γ-PGA biosynthesis. IMPORTANCE Zinc and copper are potent antimicrobial compounds. As such, bacteria have evolved a diverse range of tools to prevent metal intoxication. Here, we show that the Gram-positive model organism, Bacillus subtilis, produces poly-gamma-glutamic acid (γ-PGA) as a protective mechanism against zinc and copper intoxication and that zinc and copper dependent γ-PGA production occurs by a yet undefined mechanism independent of known γ-PGA regulation pathways.

Small RNAs couple embryonic developmental programs to gut microbes

Embryogenesis has long been known for its robustness to environmental factors. Although developmental tuning of embryogenesis to the environment experienced by the parent may be beneficial, little is understood on whether and how developmental patterns proactively change. Here, we show that Caenorhabditis elegans undergoes alternative embryogenesis in response to maternal gut microbes. Harmful microbes result in altered endodermal cell divisions; morphological changes, including left-right asymmetric development; double association between intestinal and primordial germ cells; and partial rescue of fecundity. The miR-35 microRNA family, which is controlled by systemic endogenous RNA interference and targets the β-transducin repeat-containing protein/cell division cycle 25 (CDC25) pathway, transmits intergenerational information to regulate cell divisions and reproduction. Our findings challenge the widespread assumption that C. elegans has an invariant cell lineage that consists of a fixed cell number and provide insights into how organisms optimize embryogenesis to adapt to environmental changes through epigenetic control.

Recent Advances in Microbial Synthesis of Poly-γ-Glutamic Acid: A Review

Poly-γ-glutamic acid (γ-PGA) is a natural, safe, non-immunogenic, biodegradable, and environmentally friendly glutamic biopolymer. γ-PGA has been regarded as a promising bio-based materials in the food field, medical field, even in environmental engineering field, and other industrial fields. Microbial synthesis is an economical and effective way to synthesize γ-PGA. Bacillus species are the most widely studied producing strains. γ-PGA biosynthesis involves metabolic pathway of racemization, polymerization, transfer, and catabolism. Although microbial synthesis of γ-PGA has already been used extensively, productivity and yield remain the major constraints for its industrial application. Metabolic regulation is an attempt to solve the above bottleneck problems and meet the demands of commercialization. Therefore, it is important to understand critical factors that influence γ-PGA microbial synthesis in depth. This review focuses on production strains, biosynthetic pathway, and metabolic regulation. Moreover, it systematically summarizes the functional properties, purification procedure, and industrial application of γ-PGA.

Enhanced production of poly-γ-glutamic acid via optimizing the expression cassette of Vitreoscilla hemoglobin in Bacillus licheniformis

Poly-γ-glutamic acid (γ-PGA) is a natural polymer with various applications, and its high-viscosity hinders oxygen transmission and improvement of synthesis level. Vitreoscilla hemoglobin (VHB) has been introduced into various hosts as oxygen carrier, however, its expression strength and contact efficiency with oxygen hindered efficient oxygen transfer and metabolite synthesis. Here, we want to optimize the expression cassette of VHB for γ-PGA production. Firstly, our results implied that γ-PGA yields were enhanced when introducing twin-arginine translocation (Tat) signal peptides (SP_YwbN, SP_PhoD and SP_TorA) into VHB expression cassette, and the best performance was attained by SP_YwbN from Bacillus subtilis, the γ-PGA yield of which was 18.53% higher than that of control strain, and intracellular ATP content and oxygen transfer coefficient (K_La) were increased by 29.71% and 73.12%, respectively, indicating that VHB mediated by SP_YwbN benefited oxygen transfer and ATP generation for γ-PGA synthesis. Furthermore, four promoters were screened, and P_vgb was proven as the more suitable promoter for VHB expression and γ-PGA synthesis, and γ-PGA yield of attaining strain WX/pPvgb-YwbN-Vgb was further increased to 40.59 g/L by 10.18%. Finally, WX/pPvgb-YwbN-Vgb was cultivated in 3 L fermentor for fed-batch fermentation, and 46.39 g/L γ-PGA was attained by glucose feeding, increased by 49.26% compared with the initial yield (31.01 g/L). Taken together, this study has attained an efficient VHB expression cassette for oxygen transfer and γ-PGA synthesis, which could also be applied in the production of other metabolites.

Antibacterial Hydrogels Derived from Poly(γ-glutamic acid) Nanofibers

Biocompatible hydrogels with antibacterial properties derived from γ-polyglutamic acid (γ-PGA) were prepared from bulk and electrospun nanofibers. The antibacterial drugs loaded in these hydrogels were triclosan (TCS), chlorhexidine (CHX) and polyhexamethylene biguanide (PHMB); furthermore, bacteriophages were loaded as an alternative antibacterial agent. Continuous and regular γ-PGA nanofibers were successfully obtained by the electrospinning of trifluoroacetic acid solutions in a narrow polymer concentration range and restricted parameter values of flow rate, voltage and needle-collector distance. Hydrogels were successfully obtained by using cystamine as a crosslinking agent following previous published procedures. A closed pore structure was characteristic of bulk hydrogels, whereas an open but structurally consistent structure was found in the electrospun hydrogels. In this case, the morphology of the electrospun nanofibers was drastically modified after the crosslinking reaction, increasing their diameter and surface roughness according to the amount of the added crosslinker. The release of TCS, CHX, PHMB and bacteriophages was evaluated for the different samples, being results dependent on the hydrophobicity of the selected medium and the percentage of the added cystamine. A high efficiency of hydrogels to load bacteriophages and preserve their bactericide activity was demonstrated too.