γ-PGA Concentration Research Articles

Rheology, physicochemical properties, and microstructure of fish gelatin emulsion gel modified by γ-polyglutamic acid.

In this work, the effect of the addition of γ-polyglutamic acid (γ-PGA) on the rheology, physicochemical properties, and microstructure of fish gelatin (FG) emulsion gel was investigated. Samples of the emulsion gel were evaluated for rheological behavior and stability prior to gelation. The mechanical properties and water-holding capacity (WHC) of the emulsion were determined after gelation. The microstructure of the emulsion gel was further examined using confocal laser scanning microscopy (CLSM). The results indicated a gradual increase in the apparent viscosity and gelation temperature of the emulsion at a higher concentration of γ-PGA. Additionally, frequency scan results revealed that on the addition of γ-PGA, FG emulsion exhibited a stronger structure. The emulsion containing 0.1% γ-PGA exhibited higher stability than that of the control samples. The WHC and gel strength of the emulsion gel increased on increasing the γ-PGA concentration. CLSM images showed that the addition of γ-PGA modified the structure of the emulsion gel, and the droplets containing 0.1% γ-PGA were evenly distributed. Moreover, γ-PGA could regulate the droplet size of the FG emulsion and its size distribution. These findings suggest that the viscoelasticity and structure of FG emulsion gels could be regulated by adjusting the γ-PGA concentration. The γ-PGA-modified FG emulsion gel also exhibited improved rheology and physicochemical properties. The results showed that γ-PGA-modified FG emulsion gel may find potential applications in food, medicine, cosmetics, and other industries.

Electrofermentation increases concentration of poly γ-glutamic acid in Bacillus subtilis biofilms.

Fluctuations in redox conditions in bioprocesses can alter the end-products, reduce their concentration, and lengthen the process time. Electrofermentation enables rapid metabolic modulation of biosynthesis and allows control of redox imbalances in biofilm-based fermentation processes. In this study, electrofermentation is used to boost the production of the bacterial biopolymer poly-γ-glutamic acid (γ-PGA) from Bacillus subtilis ATCC 6051. When compared to control experiments (3.3 ± 0.99 g L-1 ), the application of an electrode potential E = 0.4 V versus Ag/AgCl results in a more than two-fold increase in the production of γ-PGA (9.13 ± 1.4 g L-1 ). Using an engineered B. subtilis strain, in which γ-PGA production is driven by isopropyl β-d-1-thiogalactopyranoside, electrofermentation improves polymer concentrations from 15.4 ± 1.5 to 23.1 ± 1.6 versus g L-1 . These results confirm that electrofermentation conditions can be adopted to increase the concentration of γ-PGA and perhaps other extracellular biopolymers in industrial strains.

The influence of γ-PGA on the quality of cooked frozen crayfish during temperature fluctuations

The purpose of this study was to compare the influences of gamma-poly glutamic acid (γ-PGA) (1, 2, 3, and 4 %) to see which could outperform conventional cryoprotectant mixture (4 % sorbitol + 4 % sucrose) on cooked crayfish properties, such as physicochemical, textural qualities, oxidation reaction, water distributions, and microstructure integrity, during different freeze–thaw cycles. Crayfish quality characteristics improved significantly as γ-PGA concentration increased compared to control samples.Adding γ-PGA 4 % reduced the carbonyl content from 4.20 to 3.00 nmol/ mg protein during fluctuation-1 (F1), and from 4.15 to 2.80 nmol/ mg protein during fluctuation-2 (F2) compared to control samples. Furthermore, it increased the total sulfhydryl content from 4.15 and 4.76 to 6.19 and 6.47 mol/105 g protein during F1 and F2 and after five freeze–thaw cycles (FTC). This suggests that this concentration was more effective at controlling protein changes than other concentrations. γ-PGA generally enhanced the water-holding capacity by preventing protein denaturation and limiting ice crystal recrystallization. As a result, microstructure stability was evident, texture degradation was avoided, and the crayfish's color was preserved.

The effect of gamma-poly glutamic acid as a cryoprotectant on crayfish physicochemical and texture properties during frozen storage

Because of the potential health risks associated with current cryoprotectants, there is a need for cryoprotectants with a high level of safety. The feasibility of two gamma-polyglutamic acid concentrations (2 and 4%) as cryoprotectants compared to a conventional cryoprotectant mixture of 4% sucrose + 4% sorbitol (S–S) on the quality of cooked crayfish during a 2-month storage period at −20 °C was investigated in this study. Microstructural imaging demonstrated that γ-PGA treatments restrict the formation of ice crystals in muscle fibers, thereby slowing the progression of crayfish muscle fiber damage during storage. When treated with 2% and 4% γ-PGA, the total sulfhydryl and carbonyl contents were 4.45 and 5.14 mol/105 g protein and 3.68 and 3.17 nmol/mg protein, respectively, compared to the control sample, which had 3.94 mol/105 g protein and 4.04 nmol/mg protein at the end of storage. Furthermore, samples treated with 2 and 4% γ-PGA increased their water-holding capacity from 61.54 to 65.14 and 71.64%, respectively, compared to the control sample. This demonstrates the potency and efficiency of the 4% γ-PGA concentration. Our study could provide useful guidelines for using γ-PGA as an effective cryoprotectant rather than sucrose-sorbitol mixtures in frozen crayfish preservation and related products.

Implication of organic solvents in the precipitation of γ-polyglutamic acid for application as a sustainable flocculating agent

γ-Polyglutamic (γ-PGA) acid is a homopolyamide composed of D- and l-glutamic acid units. It is an anionic biopolymer that has properties such as water solubility, non-toxicity, and biodegradability. γ-PGA, has many environmental applications, including use as an increment to the flocculation process in water treatment. This study evaluated the extraction and quantification of γ-PGA using different organic solvents, following by application as a sustainable flocculating agent. The results demonstrate that the use of methanol was able to precipitate 6.83 mg γ-PGA g−1 natto, followed by 5.44 and 4.24 mg γ-PGA g−1 natto, respectively for ethanol and acetone. The adoption of refrigeration (12 h) is an advantage to increase the yield of the biopolymer for methanol (46.27%), ethanol (52.25%), and acetone (14.25%) as a precipitating agent. The γ-PGA yield increased in overnight extraction with ethanol, enabling the use of ethanol as an alternative to methanol. Due to steric stabilization, it was observed that increasing the γ-PGA concentration resulted in a reduction in the flocculation rate. The highest flocculation rate (92.9%) was achieved at 10 mg L−1 of γ-PGA extracted with methanol, followed by acetone at 10 mg L−1 of γ-PGA (92.43%) and ethanol at 5 mg L−1 of γ-PGA (92.2%).

Microbial Poly-γ-Glutamic Acid (γ-PGA) as an Effective Tooth Enamel Protectant.

Poly-γ-glutamic acid (γ-PGA) is a bio-derived water-soluble, edible, non-immunogenic nylon-like polymer with the biochemical characteristics of a polypeptide. This Bacillus-derived material has great potential for a wide range of applications, from bioremediation to tunable drug delivery systems. In the context of oral care, γ-PGA holds great promise in enamel demineralisation prevention. The salivary protein statherin has previously been shown to protect tooth enamel from acid dissolution and act as a reservoir for free calcium ions within oral cavities. Its superb enamel-binding capacity is attributed to the L-glutamic acid residues of this 5380 Da protein. In this study, γ-PGA was successfully synthesised from Bacillus subtilis natto cultivated on supplemented algae media and standard commercial media. The polymers obtained were tested for their potential to inhibit demineralisation of hydroxyapatite (HAp) when exposed to caries simulating acidic conditions. Formulations presenting 0.1, 0.25, 0.5, 0.75, 1, 2, 3 and 4% (w/v) γ-PGA concentration were assessed to determine the optimal conditions. Our data suggests that both the concentration and the molar mass of the γ-PGA were significant in enamel protection (p = 0.028 and p < 0.01 respectively). Ion Selective Electrode, combined with Fourier Transform Infra-Red studies, were employed to quantify enamel protection capacity of γ-PGA. All concentrations tested showed an inhibitory effect on the dissolution rate of calcium ions from hydroxyapatite, with 1% (wt) and 2% (wt) concentrations being the most effective. The impact of the average molar mass (M) on enamel dissolution was also investigated by employing commercial 66 kDa, 166 kDa, 440 kDa and 520 kDa γ-PGA fractions. All γ-PGA solutions adhered to the surface of HAp with evidence that this remained after 60 min of continuous acidic challenge. Inductively Coupled Plasma analysis showed a significant abundance of calcium ions associated with γ-PGA, which suggests that this material could also act as a responsive calcium delivery system. We have concluded that all γ-PGA samples tested (commercial and algae derived) display enamel protection capacity regardless of their concentration or average molar mass. However, we believe that γ-PGA D/L ratios might affect the binding more than its molar mass.

Efficient molasses utilization for low-molecular-weight poly-γ-glutamic acid production using a novel Bacillus subtilis strain

BackgroundPoly-γ-glutamic acid (γ-PGA) is a biopolymer and has various applications based on its biocompatibility, non-toxicity, and edibility. Low-molecular-weight (Mw)-γ-PGA has promising applications in agriculture and pharmaceuticals. It is traditionally produced by enzymatic hydrolysis. Cost-effective bioproduction of low-Mw-γ-PGA is essential for commercial application of γ-PGA.ResultsBacillus subtilis 242 is a newly isolated low-Mw-γ-PGA-producing strain. To develop cost-effective production of γ-PGA using this newly isolated strain, cane molasses and corn steep liquor were used to produce γ-PGA. The concentration of cane molasses was optimized and 100 g/L cane molasses resulted in high γ-PGA production. The effects of yeast extract and corn steep liquor on γ-PGA yield were investigated. High concentration of γ-PGA was obtained in the medium with corn steep liquor. A concentration of 32.14 g/L γ-PGA was achieved in fed-batch fermentation, with a productivity of 0.67 g/L/h and a percentage yield (gγ-PGA/gglutamate) of 106.39%. The Mw of γ-PGA was 27.99 kDa.ConclusionThis study demonstrated the potential application of B. subtilis 242 for cost-effective production of low-Mw-γ-PGA from cane molasses.

γ-PGA Fermentation by Bacillus subtilis PG-001 with Glucose Feedback Control pH-stat Strategy.

Poly-γ-glutamic acid (γ-PGA) is an important biopolymer with many applications due to its biodegradable and non-toxic characteristics. γ-PGA is produced industrially by fermentation of Bacillus species. The optimal pH range for producing γ-PGA by Bacillus subtilis PG-001 was firstly studied by glucose fed-batch fermentation with non-controlled pH. Result showed that both cell growth and γ-PGA synthesis were repressed when pH was lower than pH 6. Further investigation with γ-PGA fed-batch fermentation showed that pH 6.5 is more suitable for γ-PGA fermentation than pH 7. Under comparable consumption of glutamic acid and glucose, 11.8 g/L γ-PGA and 0.7 g/g yield were achieved by fermentation at pH 6.5, which was significantly higher than 10.5 g/L and 0.56 g/g yield of fermentation at pH 7. In addition, γ-PGA degradation during later phase of fermentation was repressed at pH 6.5 as 9238cP of final broth viscosity was achieved from fermentation at pH 6.5 while it was only 346 cP for fermentation at pH 7. Finally, a glucose feedback control pH-stat strategy was performed for reducing alkali consumption during γ-PGA fermentation, which further increased final γ-PGA concentration to 15.5 g/L with much higher viscosity (11458 cP); meanwhile the consumption of alkali decreased 57%. The fed-batch γ-PGA fermentation with glucose feedback control pH-stat strategy showed high feasibility for industrial scaling-up.

Poly-γ-glutamic acid production by simultaneous saccharification and fermentation using corn straw and its fertilizer synergistic effect evaluation.

Agricultural wastes rich in lignocellulosic biomass have been used in the production of poly-γ-glutamic acid (γ-PGA) through separate hydrolysis and fermentation (SHF), but this process is complicated and generates a lot of wastes. In order to find a simpler and greener way to produce γ-PGA using agricultural wastes, this study attempted to establish simultaneous saccharification and fermentation (SSF) with citric acid-pretreated corn straw. The possibility of Bacillus amyloliquefaciens JX-6 using corn straw as substrate to synthesize γ-PGA was validated, and the results showed that increasing the proportion of glucose in the substrate could improve the γ-PGA yield. Based on these preliminary results, the corn straw was pretreated using citric acid. Then, the liquid fraction (xylan-rich) was used for cultivation of seed culture, and the solid fraction (glucan-rich) was used as the substrate for SSF. In a 10-L fermenter, the maximum cumulative γ-PGA concentration in batch and fed-batch SSF were 5.08 ± 0.78g/L and 10.78 ± 0.32g/L, respectively. Moreover, the product from SSF without γ-PGA extraction was used as a fertilizer synergist, increasing the yield of pepper by 13.46% (P < 0.05). Our study greatly simplified the production steps of γ-PGA, and each step achieved zero emission as far as possible. The SSF process for γ-PGA production provided a simple and green way for lignocellulose biorefinery and sustainable cultivation in agriculture.

Bacillus amyloliquefaciens (IAE635) and their metabolites could purify pollutants, Vibrio spp. and coliform bacteria in coastal aquaculture wastewater

High-density aquaculture often causes the emission of polluted water to the marine environment in the coastal areas of China. To solve the aquaculture-related water quality problems, it is appropriate to adapt eco-friendly methods, such as using microbes and their metabolic products to purify polluted water. In this study, the purifying effects of Bacillus amyloliquefaciens (IAE635) metabolites (poly-γ-glutamic acid; PP) and IAE635 combined with their metabolites (MP) on turbidity, COD, NO3–-N, NH4+-N, Vibrio spp. and coliform bacteria in coastal aquaculture wastewater were conducted in the lab and in situ ponds. The results showed that the removal of turbidity, COD, NH4+-N and NO3–-N with PP and MP was more significant (p < 0.05). Compared to Control treatment (Co), the turbidity, COD, NH4+-N and NO3–-N concentrations at 24th hour were evidently reduced by 86.6%, 87.5%, 83.3% and 58.0% for PP, 87.9%, 93.5%, 86.5% and 78.0% for MP, respectively. The populations of water pathogens under PP and MP were also significantly (p < 0.05) removed compared with those of Co; at 24th hour, the Vibrio spp. and coliform bacteria were decreased by 68.7% and 66.3% for PP, 75.0% and 67.1% for MP, respectively. The water purifying effect of MP was slightly better than that of PP. In situ pond purification test demonstrated that MP significantly lowered the concentrations of turbidity, COD, NH4+-N, NO3–-N and NO2–-N, which was more effective than EM. A significantly higher (p < 0.05) γ-PGA concentration and the total bacterial population for MP compared to PP indicated that MP purifies the coastal aquaculture wastewater by both flocculation and microbial decomposition. The application of MP will benefit the aquaculture industry by providing a novel method for the removal of chemical pollutants and pathogens. Keywords: coastal aquaculture, Bacillus amyloliquefaciens and their metabolites (MP), bio-flocculants, chemical pollutants, Vibrio spp., coliform bacteria, wastewater purification DOI: 10.25165/j.ijabe.20211402.6082 Citation: Shao Y L, Zhong H, Wang L K, Elbashier M M A. Bacillus amyloliquefaciens (IAE635) and their metabolites could purify pollutants, Vibrio spp. and coliform bacteria in coastal aquaculture wastewater. Int J Agric & Biol Eng, 2021; 14(2): 205–210.

Bacillus amyloliquefaciens (IAE635) and their metabolites could purify pollutants, Vibrio spp. and coliform bacteria in coastal aquaculture wastewater

High-density aquaculture often causes the emission of polluted water to the marine environment in the coastal areas of China. To solve the aquaculture-related water quality problems, it is appropriate to adapt eco-friendly methods, such as using microbes and their metabolic products to purify polluted water. In this study, the purifying effects of Bacillus amyloliquefaciens (IAE635) metabolites (poly-γ-glutamic acid; PP) and IAE635 combined with their metabolites (MP) on turbidity, COD, NO3–-N, NH4+-N, Vibrio spp. and coliform bacteria in coastal aquaculture wastewater were conducted in the lab and in situ ponds. The results showed that the removal of turbidity, COD, NH4+-N and NO3–-N with PP and MP was more significant (p < 0.05). Compared to Control treatment (Co), the turbidity, COD, NH4+-N and NO3–-N concentrations at 24th hour were evidently reduced by 86.6%, 87.5%, 83.3% and 58.0% for PP, 87.9%, 93.5%, 86.5% and 78.0% for MP, respectively. The populations of water pathogens under PP and MP were also significantly (p < 0.05) removed compared with those of Co; at 24th hour, the Vibrio spp. and coliform bacteria were decreased by 68.7% and 66.3% for PP, 75.0% and 67.1% for MP, respectively. The water purifying effect of MP was slightly better than that of PP. In situ pond purification test demonstrated that MP significantly lowered the concentrations of turbidity, COD, NH4+-N, NO3–-N and NO2–-N, which was more effective than EM. A significantly higher (p < 0.05) γ-PGA concentration and the total bacterial population for MP compared to PP indicated that MP purifies the coastal aquaculture wastewater by both flocculation and microbial decomposition. The application of MP will benefit the aquaculture industry by providing a novel method for the removal of chemical pollutants and pathogens. Keywords: coastal aquaculture, Bacillus amyloliquefaciens and their metabolites (MP), bio-flocculants, chemical pollutants, Vibrio spp., coliform bacteria, wastewater purification DOI: 10.25165/j.ijabe.20211402.6082 Citation: Shao Y L, Zhong H, Wang L K, Elbashier M M A. Bacillus amyloliquefaciens (IAE635) and their metabolites could purify pollutants, Vibrio spp. and coliform bacteria in coastal aquaculture wastewater. Int J Agric & Biol Eng, 2021; 14(2): 205–210.

A field pilot-scale study on heavy metal-contaminated soil washing by using an environmentally friendly agent-poly-γ-glutamic acid (γ-PGA).

In this study, a farmland contaminated by heavy metals (Cu, Zn, Ni, and Cr) was selected to evaluate the performance of poly-γ-glutamic acid (γ-PGA) on the removal of heavy metals in soil washing. The highest heavy metal concentrations at the contaminated site were Cu: 1180mg/kg, Zn: 1450mg/kg, Ni: 287mg/kg, and Cr: 316mg/kg. Batch experiments designed by Taguchi Method were conducted first to assess the effect of different washing conditions on the removal of heavy metals in laboratory. The results of batch experiments show that factors that affected the removal efficiency of heavy metals was of the order γ-PGA concentration > washing time > liquid/soil ratio > rotational speed. The optimal operating parameters for heavy metal removal were γ-PGA 3.5%, liquid/soil ratio 15/1, washing time 60min, and rotational speed 100rpm. Under the optimal conditions, up to 50.7% of the major target metal, Cu, was removed. Heavy metals in the soil were mainly Fe-Mn oxide bound and organically bound. On-site treatment using the optimal operating parameters caused 54.3% of Cu removal. When the soil was washed 3 times by γ-PGA, the removal efficiency of Cu was improved to 74.3%. After the treatment, the change in soil bacterial number was insignificant, indicating that γ-PGA is an environmentally friendly washing reagent.

Effects of γ-polyglutamic acid on the gelling properties and non-covalent interactions of fish gelatin.

The effects of γ-polyglutamic aid (γ-PGA) on the gelling properties and non-covalent interactions of fish gelatin were investigated. The gel strength and melting temperature of fish gelatin gradually increased, with increasing γ-PGA concentration, although there was no significant change when the γ-PGA concentration was greater than 0.04%. As the concentration of γ-PGA increased, the electrostatic interaction of fish gelatin increased and the hydrophobic interaction between gelatin molecules decreased. The fish gelatin system was comprised of γ-PGA concentrations of 0.04 and 0.06% showing a strong hydrogen bond. When the γ-PGA concentration increased from 0 to 0.04%, more phenolic hydroxyl groups in the tyrosine residue tended to form hydrogen bonds with the protein. However, an additional increase in γ-PGA concentration to 0.1% led to enhanced hydrogen bonding with water molecules. The results of this study showed that hydrogen bonds played an important role in improving the gelling properties of gelatin by γ-PGA.

Improving poly-(γ-glutamic acid) production from a glutamic acid-independent strain from inulin substrate by consolidated bioprocessing.

To excavate the application of Jerusalem artichoke on poly(γ-glutamic acid) (γ-PGA) production, a γ-PGA producing strain Bacillus amyloliquefaciens NX-2S154 was obtained through atmospheric and room temperature plasma mutagenesis, which produced 14.83 ± 0.31g/L of γ-PGA in batch fermentation with raw inulin extract. Simultaneous saccharification and fermentation (SSF) by adding commercial inulinase were further investigated for γ-PGA fermentation. Results showed SSF could eliminate the ineffective utilization of inulin while avoiding inhibition effect of high concentration substrate, which made γ-PGA concentration reach 18.54 ± 0.39g/L with the process being shortened by 17%. Finally, an immobilized column for reducing inulinase cost was introduced to γ-PGA production. Repeated batch cultures showed the novel bioreactor exhibited higher stability and simplicity and gave average γ-PGA concentration and productivity of 19.40 ± 0.37g/L and 0.27 ± 0.008g/L/h, respectively. This work proposes a productive method for efficient γ-PGA production using Jerusalem artichoke feedstock.

Integration of enzymatic data in Bacillus subtilis genome-scale metabolic model improves phenotype predictions and enables in silico design of poly-\u03b3-glutamic acid production strains

BackgroundGenome-scale metabolic models (GEMs) allow predicting metabolic phenotypes from limited data on uptake and secretion fluxes by defining the space of all the feasible solutions and excluding physio-chemically and biologically unfeasible behaviors. The integration of additional biological information in genome-scale models, e.g., transcriptomic or proteomic profiles, has the potential to improve phenotype prediction accuracy. This is particularly important for metabolic engineering applications where more accurate model predictions can translate to more reliable model-based strain design.ResultsHere we present a GEM with Enzymatic Constraints using Kinetic and Omics data (GECKO) model of Bacillus subtilis, which uses publicly available proteomic data and enzyme kinetic parameters for central carbon (CC) metabolic reactions to constrain the flux solution space. This model allows more accurate prediction of the flux distribution and growth rate of wild-type and single-gene/operon deletion strains compared to a standard genome-scale metabolic model. The flux prediction error decreased by 43% and 36% for wild-type and mutants respectively. The model additionally increased the number of correctly predicted essential genes in CC pathways by 2.5-fold and significantly decreased flux variability in more than 80% of the reactions with variable flux. Finally, the model was used to find new gene deletion targets to optimize the flux toward the biosynthesis of poly-γ-glutamic acid (γ-PGA) polymer in engineered B. subtilis. We implemented the single-reaction deletion targets identified by the model experimentally and showed that the new strains have a twofold higher γ-PGA concentration and production rate compared to the ancestral strain.ConclusionsThis work confirms that integration of enzyme constraints is a powerful tool to improve existing genome-scale models, and demonstrates the successful use of enzyme-constrained models in B. subtilis metabolic engineering. We expect that the new model can be used to guide future metabolic engineering efforts in the important industrial production host B. subtilis.

Adsorption of Heavy Metals Using γ-PGA Produced by &lt;i&gt;Bacillus&lt;/i&gt; &lt;i&gt;pumilus &lt;/i&gt;

Poly-γ-glutamic acid (γ-PGA) produced by Bacillus pumilus C2 was employed to remove heavy metals from sewage of magnesium - based exhaust gas cleaning system (Mg-EGCS). The components of heavy metals in the sewage were detailed analyzed. On the base of the analytical results, the effects of addition amount of γ-PGA, adsorption time, temperature and NaCl concentration on the removal efficiency of typical heavy metals were further investigated. The optimal removal rates of heavy metals were obtained at the γ-PGA dosage of 9 g/L and adsorption duration of 30 min. The γ-PGA had excellent tolerance for high temperatures up to 80°C and exhibited steady heavy metal removal efficiency in NaCl concentrations of 0 – 24%. Under the optimal conditions, the removal rates of Zn, Cr, V, Cd, Pb and Ni by γ-PGA in a real sewage of Mg-EGCS achieved 53.6%, 100%, 49.2%, 72.7%, 33.7% and 39.9% respectively.

In situ microbial remediation of crude oil-soaked marine sediments using zeolite carrier with a polymer coating

Marine oil spill pollution is an important environmental problem in the world, especially crude oil-soaked marine sediments, because they are difficult to be remediated. In this study, in situ bioremediation of oil-soaked sediment was performed in the middle of the Bohai Sea. Oil-degrading bacteria were adsorbed on powdery zeolite (PZ)/granular zeolites (GZ) surfaces and then wrapped with poly-γ glutamic acid (γ-PGA). Settling column and wave flume experiments were conducted to model marine conditions and to select appropriate biological reagents. The optimal conditions were as follows: the average diameter of GZ 3 mm, mass ratio of GZ/PZ 2:1, and concentration of γ-PGA 7%. After bioremediation, over 50% of most oil-spilled pollutants n-alkanes (C12 to C27) and polycyclic aromatic hydrocarbons were degraded in 70 days. This work resulted in a successful trial of in situ bioremediation of oil-soaked marine sediments.

Protection of Radiation-Induced DNA Damage by Functional Cosmeceutical Poly-Gamma-Glutamate.

This study compared the radioprotective effects of high-molecular-weight poly-gamma-glutamate (γ-PGA, average molecular mass 3,000 kDa) and a reduced form of glutathione (GSH, a known radioprotector) on calf thymus DNA damage. The radiation-induced DNA damage was measured on the basis of the decreased fluorescence intensity after binding the DNA with ethidium bromide. All the experiments used ⁶⁰Co gamma radiation at 1,252 Gy, representing 50% DNA damage. When increasing the concentration of γ-PGA from 0.33 to 1.65 μM, the DNA protection from radiation-induced damage also increased, with a maximum of 87% protection. Meanwhile, the maximal DNA protection when increasing the concentration of GSH was only 70%. Therefore, γ-PGA exhibited significant radioprotective effects against gamma irradiation.

A novel approach to improve poly-\u03b3-glutamic acid production by NADPH Regeneration in Bacillus licheniformis WX-02

Poly-γ-glutamic acid (γ-PGA) is an important biochemical product with a variety of applications. This work reports a novel approach to improve γ-PGA through over expression of key enzymes in cofactor NADPH generating process for NADPH pool. Six genes encoding the key enzymes in NADPH generation were over-expressed in the γ-PGA producing strain B. licheniformis WX-02. Among various recombinants, the strain over-expressing zwf gene (coding for glucose-6-phosphate dehydrogenase), WX-zwf, produced the highest γ-PGA concentration (9.13 g/L), 35% improvement compared to the control strain WX-pHY300. However, the growth rates and glucose uptake rates of the mutant WX-zwf were decreased. The transcriptional levels of the genes pgsB and pgsC responsible for γ-PGA biosynthesis were increased by 8.21- and 5.26-fold, respectively. The Zwf activity of the zwf over expression strain increased by 9.28-fold, which led to the improvement of the NADPH generation, and decrease of accumulation of by-products acetoin and 2,3-butanediol. Collectively, these results demonstrated that NADPH generation via over-expression of Zwf is as an effective strategy to improve the γ-PGA production in B. licheniformis.

Enhanced Production of Poly-γ-glutamic Acid by Bacillus licheniformis TISTR 1010 with Environmental Controls.

Bacillus licheniformis TISTR 1010 was used for glutamic acid-independent production of poly-γ-glutamic acid (γ-PGA). A fed-batch production strategy was developed involving feedings of glucose, citric acid, and ammonium chloride at specified stages of the fermentation. With the dissolved oxygen concentration controlled at ≥50% of air saturation and the pH controlled at ~7.4, the fed-batch operation at 37°C afforded a peak γ-PGA concentration of 39.9±0.3gL-1 with a productivity of 0.926±0.006gL-1h-1. The observed productivity was nearly threefold greater than previously reported for glutamic acid-independent production using the strain TISTR 1010. The molecular weight of γ-PGA was in the approximate range of 60 to 135kDa.