γ-PGA Production Research Articles

Calcium regulates glutamate dehydrogenase and poly-γ-glutamic acid synthesis in Bacillus natto.

To study the effect of Ca(2+) on glutamate dehydrogenase (GDH) and its role in poly-γ-glutamic acid (γ-PGA) synthesis in Bacillus natto HSF 1410. When the concentration of Ca(2+) varied from 0 to 0.1 g/l in the growth medium of B. natto HSF 1410, γ-PGA production increased from 6.8 to 9.7 g/l, while GDH specific activity and NH4Cl consumption improved from 183 to 295 U/mg and from 0.65 to 0.77 g/l, respectively. GDH with α-ketoglutarate as substrate primarily used NADPH as coenzyme with a K m of 0.08 mM. GDH was responsible for the synthesis of endogenous glutamate. The specific activity of GDH remained essentially unchanged in the presence of CaCl2 (0.05-0.2 g/l) in vitro. However, the specific activity of GDH and its expression was significantly increased by CaCl2 in vivo. Therefore, the regulation of GDH and PGA synthesis by Ca(2+) is an intracellular process. Calcium regulation may be an effective approach for producing γ-PGA on an industrial scale.

Whole-Genome Sequencing and Comparative Genome Analysis of Bacillus subtilis Strains Isolated from Non-Salted Fermented Soybean Foods.

Bacillus subtilis is the main component in the fermentation of soybeans. To investigate the genetics of the soybean-fermenting B. subtilis strains and its relationship with the productivity of extracellular poly-γ-glutamic acid (γPGA), we sequenced the whole genome of eight B. subtilis stains isolated from non-salted fermented soybean foods in Southeast Asia. Assembled nucleotide sequences were compared with those of a natto (fermented soybean food) starter strain B. subtilis BEST195 and the laboratory standard strain B. subtilis 168 that is incapable of γPGA production. Detected variants were investigated in terms of insertion sequences, biotin synthesis, production of subtilisin NAT, and regulatory genes for γPGA synthesis, which were related to fermentation process. Comparing genome sequences, we found that the strains that produce γPGA have a deletion in a protein that constitutes the flagellar basal body, and this deletion was not found in the non-producing strains. We further identified diversity in variants of the bio operon, which is responsible for the biotin auxotrophism of the natto starter strains. Phylogenetic analysis using multilocus sequencing typing revealed that the B. subtilis strains isolated from the non-salted fermented soybeans were not clustered together, while the natto-fermenting strains were tightly clustered; this analysis also suggested that the strain isolated from “Tua Nao” of Thailand traces a different evolutionary process from other strains.

Enhancement of poly‐γ‐glutamic acid production by alkaline pH stress treatment in Bacillus licheniformisWX‐02

AbstractBACKGROUNDThe effects of alkaline stress on γ‐PGA biosynthesis and the mechanism involved have not been investigated in glutamate‐free medium.RESULTSEffects of alkaline pH stress on the yield and molecular weight of γ‐PGA were investigated in a 50 L bioreactor, and transcriptional levels of relevant genes were measured to explain the mechanism. After alkaline stress treatment, the maximum γ‐PGA yield reached 36.26 g L−1, increased by 79% compared with the control. The transcription levels of γ‐PGA synthetase genes pgsB and pgsC, as well as their closely related regulation factors degU and swrA, were improved 18.9‐fold, 31.2‐fold, 3.0‐fold and 6.3‐fold, respectively. Moreover, transcriptional analysis showed that alkaline stress enhanced the biosynthesis of γ‐PGA precursor (glutamic acid) and reduced the formation of byproducts (acetoin and 2,3‐butanediol), which contributed to the improved production of γ‐PGA. In addition, alkaline stress reduced the γ‐PGA molecular weight, which might be due to the enhanced expression of γ‐PGA hydrolase PgdS.CONCLUSIONThe alkaline stress‐mediated strategy was developed to regulate the yield and molecular weight of γ‐PGA in the glutamate‐free medium, and the mechanism involved was explained through transcriptional analysis. © 2015 Society of Chemical Industry

Properties of Polyglutamic Acid Produced by Bacillus subtilis ATCC 6633 in Rehydrated Whey Powder Supplemented with Different Carbon Sources

In this study, the use of rehydrated whey powder (RWP) solutions containing different carbon sources (citric acid, ammonium sulfate, or glutamic acid) for γ-poly(glutamic acid) (γ-PGA) by Bacillus subtilis ATCC 6633 was explored. After 72 h of fermentation at 30℃, cell growth, γ-PGA production, molecular weight by SDS-PAGE, rheological properties and NMR analysis of γ-PGA were determined. The growth of B. subtilis was significantly different during 72 h of fermentation in RWP, medium E, and RWP containing citric acid or glutamic acid. These results showed the dynamic viscosity of the 1% polymer solution was 2.5 Pa·s at 10 1/sec shear rate. The maximum γ-PGA concentration was 1.57 g/100 mL in RWP containing glutamic acid, citric acid and ammonium sulfate. Therefore, RWP as a waste product with being efficient and more economic fermentation medium to produce γ-PGA can be ideal for the industrial production.

Improved poly-γ-glutamic acid production in Bacillus amyloliquefaciens by modular pathway engineering

A Bacillus amyloliquefaciens strain with enhanced γ-PGA production was constructed by metabolically engineering its γ-PGA synthesis-related metabolic networks: by-products synthesis, γ-PGA degradation, glutamate precursor synthesis, γ-PGA synthesis and autoinducer synthesis. The genes involved in by-products synthesis were firstly deleted from the starting NK-1 strain. The obtained NK-E7 strain with deletions of the epsA-O (responsible for extracellular polysaccharide synthesis), sac (responsible for levan synthesis), lps (responsible for lipopolysaccharide synthesis) and pta (encoding phosphotransacetylase) genes, showed increased γ-PGA purity and slight increase of γ-PGA titer from 3.8 to 4.15g/L. The γ-PGA degrading genes pgdS (encoding poly-gamma-glutamate depolymerase) and cwlO (encoding cell wall hydrolase) were further deleted. The obtained NK-E10 strain showed further increased γ-PGA production from 4.15 to 9.18g/L. The autoinducer AI-2 synthetase gene luxS was deleted in NK-E10 strain and the resulting NK-E11 strain showed comparable γ-PGA titer to NK-E10 (from 9.18 to 9.54g/L). In addition, we overexpressed the pgsBCA genes (encoding γ-PGA synthetase) in NK-E11 strain; however, the overexpression of these genes led to a decrease in γ-PGA production. Finally, the rocG gene (encoding glutamate dehydrogenase) and the glnA gene (glutamine synthetase) were repressed by the expression of synthetic small regulatory RNAs in NK-E11 strain. The rocG-repressed NK-anti-rocG strain exhibited the highest γ-PGA titer (11.04g/L), which was 2.91-fold higher than that of the NK-1 strain. Fed-batch cultivation of the NK-anti-rocG strain resulted in a final γ-PGA titer of 20.3g/L, which was 5.34-fold higher than that of the NK-1 strain in shaking flasks. This work is the first report of a systematically metabolic engineering approach that significantly enhanced γ-PGA production in a B. amyloliquefaciens strain. The engineering strategies explored here are also useful for engineering cell factories for the production of γ-PGA or of other valuable metabolites.

Enhanced poly(γ-glutamic acid) production by H2 O2 -induced reactive oxygen species in the fermentation of Bacillus subtilis NX-2.

Effects of reactive oxygen species (ROS) on cell growth and poly(γ-glutamic acid) (γ-PGA) synthesis were studied by adding hydrogen peroxide to a medium of Bacillus subtilis NX-2. After optimizing the addition concentration and time of H2 O2 , a maximum concentration of 33.9g/L γ-PGA was obtained by adding 100µM H2 O2 to the medium after 24H. This concentration was 20.6% higher than that of the control. The addition of diphenyleneiodonium chloride (ROS inhibitor) can interdict the effect of H2 O2 -induced ROS. Transcriptional levels of the cofactors and relevant genes were also determined under ROS stress to illustrate the possible metabolic mechanism contributing to the improve γ-PGA production. The transcriptional levels of genes belonging to the tricarboxylic acid cycle and electron transfer chain system were significantly increased by ROS, which decreased the NADH/NAD+ ratio and increased the ATP levels, thereby providing more reducing power and energy for γ-PGA biosynthesis. The enhanced γ-PGA synthetic genes also directly promoted the formation of γ-PGA. This study was the first to use the ROS control strategy for γ-PGA fermentation and provided valuable information on the possible mechanism by which ROS regulated γ-PGA biosynthesis in B. subtilis NX-2.

Intracellular synthesis of glutamic acid in Bacillus methylotrophicus SK19.001, a glutamate-independent poly(γ-glutamic acid)-producing strain.

Bacillus methylotrophicus SK19.001 is a glutamate-independent strain that produces poly(γ-glutamic acid) (γ-PGA), a polymer of D- and L-glutamic acids that possesses applications in food, the environment, agriculture, etc. This study was undertaken to explore the synthetic pathway of intracellular L- and D-glutamic acid in SK19.001 by investigating the effects of tricarboxylic acid cycle intermediates and different amino acids as metabolic precursors on the production of γ-PGA and analyzing the activities of the enzymes involved in the synthesis of L- and D-glutamate. Tricarboxylic acid cycle intermediates and amino acids could participate in the synthesis of γ-PGA via independent pathways in SK19.001. L-Aspartate aminotransferase, L-glutaminase and L-glutamate synthase were the enzymatic sources of L-glutamate. Glutamate racemase was responsible for the formation of D-glutamate for the synthesis of γ-PGA, and the synthetase had stereoselectivity for glutamate substrate. The enzymatic sources of L-glutamate were investigated for the first time in the glutamate-independent γ-PGA-producing strain, and multiple enzymatic sources of L-glutamate were verified in SK19.001, which will benefit efforts to improve production of γ-PGA with metabolic engineering strategies.

Production of poly-γ-glutamic acid by glutamic acid-independent Bacillus licheniformis TISTR 1010 using different feeding strategies

Bacillus licheniformis TISTR 1010 was identified as a glutamic acid-independent producer of poly-γ-glutamic acid (γ-PGA) in a newly modified B medium in a shake flask culture. The fed-batch production of γ-PGA by this strain was optimized through simultaneously and continuously feeding glucose and NH4Cl with manual and pH-stat based feeding methods in a 7-L stirred fermenter. Using the optimized operation, the dissolved oxygen concentration, the pH, the glucose concentration and NH4Cl concentration could be stably controlled to extend the γ-PGA production phase and eliminate the hydrolysis of γ-PGA. As a result, the γ-PGA concentration and productivity reached levels of 27.5±0.2gL−1 and 0.286±0.059gL−1h−1, respectively. These values of final concentration and productivity were 5-fold and 3-fold of those obtained without the optimization.

Deletion of genes involved in glutamate metabolism to improve poly-gamma-glutamic acid production in B. amyloliquefaciens LL3.

Here, we attempted to elevate poly-gamma-glutamic acid (γ-PGA) production by modifying genes involved in glutamate metabolism in Bacillus amyloliquefaciens LL3. Products of rocR, rocG and gudB facilitate the conversion from glutamate to 2-oxoglutarate in Bacillus subtillis. The gene odhA is responsible for the synthesis of a component of the 2-oxoglutarate dehydrogenase complex that catalyzes the oxidative decarboxylation of 2-oxoglutarate to succinyl coenzyme A. In-frame deletions of these four genes were performed. In shake flask experiments the gudB/rocG double mutant presented enhanced production of γ-PGA, a 38 % increase compared with wild type. When fermented in a 5-L fermenter with pH control, the γ-PGA yield of the rocR mutant was increased to 5.83 g/L from 4.55 g/L for shake flask experiments. The gudB/rocG double mutant produced 5.68 g/L γ-PGA compared with that of 4.03 g/L for the wild type, a 40 % increase. Those results indicated the possibility of improving γ-PGA production by modifying glutamate metabolism, and identified potential genetic targets to improve γ-PGA production.

Conversion of agroindustrial residues for high poly(γ-glutamic acid) production by Bacillus subtilis NX-2 via solid-state fermentation

Poly(γ-glutamic acid) (γ-PGA) production by Bacillus subtilis NX-2 was carried out through solid-state fermentation with dry mushroom residues (DMR) and monosodium glutamate production residues (MGPR; a substitute of glutamate) for the first time. Dry shiitake mushroom residue (DSMR) was found to be the most suitable solid substrate among these DMRs; the optimal DSMR-to-MGPR ratio was optimized as 12:8. To increase γ-PGA production, industrial waste glycerol was added as a carbon source supplement to the solid-state medium. As a result, γ-PGA production increased by 34.8%. The batch fermentation obtained an outcome of 115.6gkg−1 γ-PGA and 39.5×108 colony forming units g−1 cells. Furthermore, a satisfactory yield of 107.7gkg−1 γ-PGA was achieved by compost experiment on a scale of 50kg in open air, indicating that economically large-scale γ-PGA production was feasible. Therefore, this study provided a novel method to produce γ-PGA from abundant and low-cost agroindustrial residues.

Purification and characterization of gamma poly glutamic acid from newly Bacillus licheniformis NRC20

γ-poly glutamic acid (γ-PGA) has received considerable attention for pharmaceutical and biomedical applications. γ-PGA from the newly isolate Bacillus licheniformis NRC20 was purified and characterized using diffusion distance agar plate, mass spectrometry and thin layer chromatography. All analysis indicated that γ-PGA is a homopolymer composed of glutamic acid. Its molecular weight was determined to be 1266kDa. It was composed of l- and d-glutamic acid residues. An amplicon of 3050 represents the γ-PGA-coding genes was obtained, sequenced and submitted in genbank database. Its amino acid sequence showed high similarity with that obtained from B. licheniformis strains. The bacterium NRC 20 was independent of l-glutamic acid but the polymer production enhanced when cultivated in medium containing l-glutamic acid as the sole nitrogen source. Finally we can conclude that γ-PGA production from B. licheniformis NRC20 has many promised applications in medicine, industry and nanotechnology.

High-level production of poly(γ-glutamic acid) by a newly isolated glutamate-independent strain, Bacillus methylotrophicus

Poly(γ-glutamic acid) (γ-PGA) is a natural, biodegradable polyamide that is mostly produced by glutamate-dependent microorganisms such as Bacillus licheniformis, Bacillus amyloliquefaciens and Bacillus subtilis. In this study, a γ-PGA-producing glutamate-independent strain, SK19.001, was screened and characterized as Bacillus methylotrophicus. The effects of various carbon and nitrogen sources on the γ-PGA productivity of this strain were investigated. Many carbon sources, such as sodium glutamate, glucose, glycerol, soluble starch, α-lactose, maltose, sucrose, citric acid and fructose, proved suitable for SK19.001 to synthesize γ-PGA with high molecular weight. Compared with the previously reported production from glutamate-independent strains, a high level of production of γ-PGA (33.84–35.34g/L) was obtained when SK19.001 was grown in a medium containing 30g/L glycerol, 15g/L sodium citrate and 50g/L peptone. The γ-PGA product showed an ultra-high molecular weight of over 10,000kDa. The genome of B. methylotrophicus SK19.001 was sequenced and a comparative investigation revealed that the PgsB, PgsC, and PgsA protein sequences were almost identical between the glutamate-independent strains and less identical between the glutamate-independent and glutamate-dependent strains. This study is the first to demonstrate high levels of γ-PGA production using B. methylotrophicus. The results suggest a promising new approach for γ-PGA production.

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

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made up of repeating units of l-glutamic acid, d-glutamic acid or both. γ-PGA can exhibit different properties (conformational states, enantiomeric properties and molecular mass). Owing to its biodegradable, non-toxic and non-immunogenic properties, it has been used successfully in the food, medical and wastewater industries. Amongst other novel applications, it has the potential to be used for protein crystallization, as a soft tissue adhesive and a non-viral vector for safe gene delivery. This review focuses on the production, properties and applications of γ-PGA. Each application of γ-PGA utilizes specific properties attributed to various forms of γ-PGA. As a result of its growing applications, more strains of bacteria need to be investigated for γ-PGA production to obtain high yields of γ-PGA with different properties. Many medical applications (especially drug delivery) have exploited α-PGA. As γ-PGA is essentially different from α-PGA (i.e. it does not involve a chemical modification step and is not susceptible to proteases), it could be better utilized for such medical applications. Optimization of γ-PGA with respect to cost of production, molecular mass and conformational/enantiomeric properties is a major step in making its application practical. Analyses of γ-PGA production and knowledge of the enzymes and genes involved in γ-PGA production will not only help increase productivity whilst reducing the cost of production, but also help to understand the mechanism by which γ-PGA is effective in numerous applications.

Effects of metabolic pathway precursors and polydimethylsiloxane (PDMS) on poly-(gamma)-glutamic acid production by Bacillus subtilis BL53.

The aims of this study were to evaluate the effects of the addition of metabolic precursors and polydimethylsiloxane (PDMS) as an oxygen carrier to cultures of Bacillus subtilis BL53 during the production of γ-PGA. Kinetics analyses of cultivations of different media showed that B. subtilis BL53 is an exogenous glutamic acid-dependent strain. When the metabolic pathway precursors of γ-PGA synthesis, L-glutamine and a-ketoglutaric acid, were added to the culture medium, production of the biopolymer was increased by 20% considering the medium without these precursors. The addition of 10% of the oxygen carrier PDMS to cultures caused a two-fold increase in the volumetric oxygen mass transfer coefficient (kLa), improving γ-PGA production and productivity. Finally, bioreactor cultures of B. subtilis BL53 adopting the combination of optimized medium E, added of glutamine, α-ketoglutaric acid, and PDMS, showed a productivity of 1gL(-1)h(-1) of g-PGA after only 24h of cultivation. Results of this study suggest that the use of metabolic pathway precursors glutamine and a-ketolgutaric acid, combined with the addition of PDMS as an oxygen carrier in bioreactors, can improve γ-PGA production and productivity by Bacillus strains .

Physiological and metabolic analysis of nitrate reduction on poly-gamma-glutamic acid synthesis in Bacillus licheniformis WX-02.

Nitrate is an important nitrogen source for organism, but whether and how nitrate improves poly-γ-glutamic acid (γ-PGA) production of bacterial is not clear. The effect of nitrate on γ-PGA production of Bacillus licheniformis WX-02 was investigated. By addition of 50mmol/L nitrate, the γ-PGA yield reached 12.3±0.21g/L, which increased 2.3-fold compared to the control. The mechanism of enhanced γ-PGA production was further investigated by analysis of nitrate reduction, physiology, pyruvate overflow metabolism and energy synthesis. Nitrate reduction was only carried out in the middle stage of γ-PGA fermentation. The result of consumption of nutrients showed that glucose uptake was not effected and the L-glutamic acid utilization efficiency increased from 48.3 to 77.0%. The date of overflow metabolism obtained from high-performance liquid chromatography showed that the metabolism of pyruvate, formate, lactate and acetoin was both heightened by nitrate reduction, while the 2,3-butanediol biosynthesis was decreased. Meanwhile, the change of energy indicated that more ATP was synthesized during nitrate reduction. In summary, nitrate was a positive effector of γ-PGA biosynthesis in B. licheniformis WX-02 and nitrate reduction affected multi-metabolism pathways, including glycolysis, overflow metabolism and energy metabolism.

Enhanced production of poly-γ-glutamic acid by a newly-isolated Bacillus subtilis.

Application of poly-gamma-glutamic acid (γ-PGA), an unusual macromolecular anionic polypeptide, is limited due to the high cost associated with its low productivity. Screening bacterial strains to find a more efficient producer is one approach to overcome this limitation. Strain MJ80 was isolated as a γ-PGA producer among 1,500 bacterial colonies obtained from soil samples. It was identified as Bacillus subtilis, based on the biochemical and morphological properties and 16S rDNA gene sequencing. It produced γ-PGA from both glutamic acid and soybean powder, identifying it as a facultative glutamic acid-metabolizing bacterium. After optimization of its culture conditions, B. subtilis MJ80 showed γ-PGA productivity of 75.5 and 68.7g/l in 3 and 300l jar fermenters for 3days cultivation, respectively, the highest productivity reported to date, suggesting MJ80 to be a promising strain for γ-PGA production.

Metabolic engineering of Bacillus amyloliquefaciens for poly-gamma-glutamic acid (γ-PGA) overproduction.

We constructed a metabolically engineered glutamate-independent Bacillus amyloliquefaciens strain with considerable γ-PGA production. It was carried out by double-deletion of the cwlO gene and epsA-O cluster, as well as insertion of the vgb gene in the bacteria chromosome. The final generated strain NK-PV elicited the highest production of γ-PGA (5.12 g l−1), which was 63.2% higher than that of the wild-type NK-1 strain (3.14 g l−1). The γ-PGA purity also improved in the NK-PV strain of 80.4% compared with 76.8% for the control. Experiments on bacterial biofilm formation experiment showed that NK-1 and NK-c (ΔcwlO) strains can form biofilm; the epsA-O deletion NK-7 and NK-PV strains could only form an incomplete biofilm.

A markerless gene replacement method for B. amyloliquefaciens LL3 and its use in genome reduction and improvement of poly-γ-glutamic acid production.

We herein adapted a markerless gene replacement method by combining a temperature-sensitive plasmid pKSV7 with a counterselectable marker, the upp gene encoding uracil phosphoribosyltransferase (UPRTase), for the poly-γ-glutamic acid (γ-PGA)-producing strain Bacillus amyloliquefaciens LL3. Deletion of the upp gene conferred LL3 5-fluorouracil (5-FU) resistance. Sensitivity to 5-FU was restored when LL3 Δupp was transformed with pKSV7-based deletion plasmid which carries a functional allele of the upp gene of Bacillus subtilis 168. These observations allowed us to adapt a two-step plasmid integration and excision strategy to perform markerless deletion of genes of interest. Deletion plasmid harboring a mutant allele of the target gene was first integrated in the genome by culturing cells under nonpermissive conditions for pKSV7 replication. Single-crossover recombinants were then grown without antibiotics to aid the second recombinational event. 5-FU was used to select for double-crossover recombinants with plasmid evicted from the chromosome. The resulting recombinants either harbored the wild-type or mutated allele of the target gene and could be identified by PCR and DNA sequencing. Using this method, we successively removed the amyA gene and a 47-kb fragment of the bae cluster from the genome of LL3, with higher efficiency compared with previous reports. We also investigated the effects of a transcriptional regulator, RocR, on γ-PGA production and cell growth. Specific γ-PGA production of the rocR mutant was increased by 1.9-fold, which represents a new way to improve γ-PGA production.

Functions of poly-gamma-glutamic acid (γ-PGA) degradation genes in γ-PGA synthesis and cell morphology maintenance.

Poly-γ-glutamic acid (γ-PGA) is an important biopolymer with greatly potential in industrial and medical applications. In the present study, we constructed a metabolically engineered glutamate-independent Bacillus amyloliquefaciens LL3 strain with considerable γ-PGA production, which was carried out by single, double, and triple markerless deletions of three degradation genes pgdS, ggt, and cwlO. The highest γ-PGA production (7.12 g/L) was obtained from the pgdS and cwlO double-deletion strain NK-pc, which was 93 % higher than that of wild-type LL3 strain (3.69 g/L). The triple-gene-deletion strain NK-pgc showed a 28 % decrease in γ-PGA production, leading to a yield of 2.69 g/L. Furthermore, the cell morphologies of the mutant strains were also characterized. The cell length of cwlO deletion strains NK-c and NK-pc was shorter than that of the wild-type strain, while the ggt deletion strains NK-g, NK-pg, NK-gc, and NK-pgc showed longer cell lengths. This is the first report concerning the markerless deletion of γ-PGA degradation genes to improve γ-PGA production in a glutamate-independent strain and the first observation that γ-glutamyltranspeptidase (encoded by ggt) could be involved in the inhibition of cell elongation.

Improved production of poly-γ-glutamic acid by Bacillus subtilis D7 isolated from Doenjang, a Korean traditional fermented food, and its antioxidant activity.

The objectives of this study was to improve poly-γ-glutamic acid (γ-PGA) production by Bacillus subtilis D7 isolated from a Korean traditional fermented food and to assess its antioxidant activity for applications in the cosmetics and pharmaceutical industries. Strain D7 produced γ-PGA in the absence of L-glutamic acid, indicating L-glutamic acid-independent production. However, the addition of L-glutamic acid increased γ-PGA production. Several tricarboxylic acid cycle intermediates and amino acids could serve as the metabolic precursors for γ-PGA production, and the addition of pyruvic acid and D-glutamic acid to culture medium improved the yield of γ-PGA markedly. The maximum yield of γ-PGA obtained was 24.93 ± 0.64g/l in improved medium, which was about 5.4-fold higher than the yield obtained in basal medium. γ-PGA was found to have 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (46.8 ± 1.5%), hydroxyl radical scavenging activity (52.0 ± 1.8%), 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS) radical scavenging activity (42.1 ± 1.8%), nitric oxide scavenging activity (35.1 ± 1.3%), reducing power (0.304 ± 0.008), and metal chelating activity (91.3 ± 3.5%). These results indicate that γ-PGA has a potential use in the food, cosmetics, and biomedical industries for the development of novel products with radical scavenging activity. As far as we are aware, this is the first report to describe the antioxidant activityof γ-PGA produced by bacteria.