Molecular cloning, expression, and immobilization of glutamate decarboxylase from Lactobacillus fermentum YS2

Production of γ-aminobutyric acid by immobilization of two Yarrowia lipolytica glutamate decarboxylases on electrospun nanofibrous membrane

This study harnesses glutamate decarboxylase (GAD) from Yarrowia lipolytica to improve the biosynthesis of γ-aminobutyric acid (GABA), focusing on boosting the enzyme's catalytic efficiency and stability by immobilizing it on nanofibrous membranes. Through recombinant DNA techniques, two GAD genes, YlGAD1 and YlGAD2, were cloned from Yarrowia lipolytica and then expressed in Escherichia coli. Compared to their soluble forms, the immobilized enzymes exhibited significant improvements in thermal and pH stability and increased resistance to chemical denaturants. The immobilization notably enhanced substrate affinity, as evidenced by reduced Km values and increased kcat values, indicating heightened catalytic efficiency. Additionally, the immobilized YlGAD1 and YlGAD2 enzymes showed substantial reusability, maintaining 50% and 40% of their activity, respectively, after six consecutive cycles. These results underscore the feasibility of employing immobilized YlGAD enzymes for cost-effective and environmentally sustainable GABA production. This investigation not only affirms the utility of YlGADs in GABA synthesis but also underscores the advantages of enzyme immobilization in industrial settings, paving the way for scalable biotechnological processes.

Contributions of Gamma-Aminobutyric Acid (GABA) Produced by Lactic Acid Bacteria on Food Quality and Human Health: Current Applications and Future Prospects

The need to increase food safety and improve human health has led to a worldwide increase in interest in gamma-aminobutyric acid (GABA), produced by lactic acid bacteria (LABs). GABA, produced from glutamic acid in a reaction catalyzed by glutamate decarboxylase (GAD), is a four-carbon, non-protein amino acid that is increasingly used in the food industry to improve the safety/quality of foods. In addition to the possible positive effects of GABA, called a postbiotic, on neuroprotection, improving sleep quality, alleviating depression and relieving pain, the various health benefits of GABA-enriched foods such as antidiabetic, antihypertension, and anti-inflammatory effects are also being investigated. For all these reasons, it is not surprising that efforts to identify LAB strains with a high GABA productivity and to increase GABA production from LABs through genetic engineering to increase GABA yield are accelerating. However, GABA's contributions to food safety/quality and human health have not yet been fully discussed in the literature. Therefore, this current review highlights the synthesis and food applications of GABA produced from LABs, discusses its health benefits such as, for example, alleviating drug withdrawal syndromes and regulating obesity and overeating. Still, other potential food and drug interactions (among others) remain unanswered questions to be elucidated in the future. Hence, this review paves the way toward further studies.

Gut health benefits and associated systemic effects provided by functional components from the fermentation of natural matrices

Recently, the role of the gut microbiota in metabolic health, immunity, behavioral balance, longevity, and intestine comfort has been the object of several studies from scientific communities. They were encouraged by a growing interest from food industries and consumers toward novel fermented ingredients and formulations with powerful biological effects, such as pre, pro, and postbiotic products. Depending on the selected strains, the operating conditions, the addition of suitable reagents or enzymes, the equipment, and the reactor configurations, functional compounds with high bioactivity, such as short-chain fatty acids, gamma-aminobutyric acid, bioactive peptides, and serotonin, can be enhanced and/or produced through fermentation of several vegetable matrices. Otherwise, their formation can also be promoted directly in the gut after the dietary intake of fermented foods: In this case, fermentation will aim to increase the content of precursor substances, such as indigestible fibers, polyphenols, some amino acids, and resistant starch, which can be potentially metabolized by endogenous gut microorganisms and converted in healthy molecules. This review provides an overview of the main functional components currently investigated in literature and the associated gut health benefits. The current state of the art about fermentation technology as a promising functionalization tool to promote the direct or indirect formation of gut-health-enhancing components was deepened, highlighting the importance of optimizing microorganism selection, system setups, and process conditions according to the target compound of interest. The collected data suggested the possibility of gaining novel functional food ingredients or products rich in functional molecules through fermentation without performing additional extraction and purification stages, which are needed when conventional culture broths are used.

Site-directed immobilization of enzymes on nanoparticles using self-assembly systems

Enzyme immobilization is an effective method for improving the stability and reusability. However, linking at random sites on the enzyme results in low catalytic efficiency due to blockage of the active site or conformational changes. Therefore, controlling the orientation of enzymes on the carrier has been developed. Here, the site-specific mutation and the SpyTag/SpyCatcher systems were used to prepare a site-directed immobilized enzyme. The thermal stability of the immobilized enzyme was better than that of the free enzyme, and ≥80 % of the catalytic activity was retained after 30 days of storage. Furthermore, the Michaelis constant (Km) and the turnover number (kcat) of the immobilized enzyme were 5.23-fold lower and 6.11-fold higher than those of the free enzyme, respectively, which appeared to be related to changes in secondary structure after immobilization. These findings provide a new and effective option for enzyme-directed immobilization.

GABA synthesizing lactic acid bacteria and genomic analysis of Levilactobacillus brevis LAB6

This study was conducted to investigate the γ-aminobutyric acid (GABA) production ability of 20 Lactobacillus and 25 Bifidobacterium strains which were previously isolated in our laboratory. Effect of initial pH, incubation time, monosodium glutamate (MSG), and pyridoxal-5'-phosphate (PLP) concentration for highest GABA production by two potent bacterial strains, Levilactobacillus brevis LAB6 and Limosilactobacillus fermentum LAB19 were optimized in the MRS media. A threefold increase in GABA production at an initial pH 4.0, incubation time of 120 h in medium supplemented with 3% MSG and 400 μM of PLP for LAB6 and 300 μM for LAB19 lead to the production of 19.67 ± 0.28 and 20.77 ± 0.14 g/L of GABA, respectively. Coculturing both strains under optimized conditions led to a GABA yield of 20.02 ± 0.17 g/L. Owing to potent anti-inflammatory activity in-vitro, as reported previously, and highest GABA production ability of LAB6 (MTCC 25662), its whole-genome sequencing and bioinformatics analysis was carried out for mining genes related to GABA metabolism. LAB6 harbored a complete glutamate decarboxylase (GAD) gene system comprising gadA, gadB, and gadC as well as genes responsible for the beneficial probiotic traits, such as for acid and bile tolerance and host adhesion. Comparative genomic analysis of LAB6 with 28 completely sequenced Levilactobacillus brevis strains revealed the presence of 95 strain-specific genes-families that was significantly higher than most other L. brevis strains.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03918-7.

Biosynthesis of Gamma-Aminobutyric Acid (GABA) by Lactiplantibacillus plantarum in Fermented Food Production

In recent decades, given the important role of gamma-aminobutyric acid (GABA) in human health, scientists have paid great attention to the enrichment of this chemical compound in food using various methods, including microbial fermentation. Moreover, GABA or GABA-rich products have been successfully commercialized as food additives or functional dietary supplements. Several microorganisms can produce GABA, including bacteria, fungi, and yeasts. Among GABA-producing microorganisms, lactic acid bacteria (LAB) are commonly used in the production of many fermented foods. Lactiplantibacillus plantarum (formerly Lactobacillus plantarum) is a LAB species that has a long history of natural occurrence and safe use in a wide variety of fermented foods and beverages. Within this species, some strains possess not only good pro-technological properties but also the ability to produce various bioactive compounds, including GABA. The present review aims, after a preliminary excursus on the function and biosynthesis of GABA, to provide an overview of the current uses of microorganisms and, in particular, of L. plantarum in the production of GABA, with a detailed focus on fermented foods. The results of the studies reported in this review highlight that the selection of new probiotic strains of L. plantarum with the ability to synthesize GABA may offer concrete opportunities for the design of new functional foods.

A Novel Method for γ-Aminobutyric Acid Biosynthesis Using Glutamate Decarboxylase Entrapped in Polyvinyl Alcohol-Sodium Alginate Capsules

γ-aminobutyric acid (GABA) has essential physiological functions in the human body. A novel method using glutamate decarboxylase (GAD) entrapped in polyvinyl alcohol (PVA)-sodium alginate (SA) capsules provides a green biological strategy for GABA synthesis. In this investigation, the stability range of immobilized GAD was effectively broadened, and immobilized GAD could be repeatedly used as a batch and fixed-bed column catalyst. The immobilized enzymes were stable and retained 89% of their activity in a pH range of 4.0-5.6, while there was an approximately 50% decrease in free GAD activity in the pH range of 4.8 ± 0.4. The immobilized GAD affinity to the substrate improved, and this was evidenced by the apparent decrease in Km to 13.3 mmol/L from the 30.9 mmol/L for free GAD. The immobilized GAD retained >90.6% activity after eight cycles and a near-100% enzyme activity retention after 120 h of a continuous fixed-bed column catalyst operation. This study has thus presented an effective PVA-SA-GAD immobilization method that could be used to continuously scale-up GABA biosynthesis.

Expression and Transformation Characteristics of a Novel Glutamic Acid Decarboxylase LcGAD10s and Its Application on Sufu Processing

Gamma-aminobutyric acid (GABA) is an important non-proteinogenic amino acid and a potent bioactive compound with many anti-hypertensive and anti-depressant activities. The bioconversion of GABA by glutamic acid decarboxylase (GAD) has been eagerly studied. Herein, novel pyridoxal-5-phosphate monohydrates (PLP)-dependent GAD, which is not quite similar to reporting, was cloned from Latilactobacillus curvatus and efficiently expressed in E. coli. The conveniently purified GAD (designated LcGAD10s) appeared as a single protein on SDS-PAGE with a molecular mass of 52.0 kDa. LcGAD10s exhibited a specific activity of 303.7 U/mg after purification by Ni-IDA affinity chromatography, with optimal activity at 55 °C and pH 5. LcGAD10s displayed excellent temperature (50 °C) and pH (4-8) stability which relative activity above 80% and 70%, respectively. The enzymatic activity was, respectively, increased and depressed by 130%, and 24% in the presence of Mn+ and Cu2+. Enzyme activity over 90% can be achieved by adding at least 25 mM of PLP. LcGAD10s was able to efficiently transform 15 g/L GABA with a single-factor optimized reaction of pH (5), temperature (50 °C), time (2 h), LcGAD10s dosage (0.4 U) and monosodium glutamate level (5 g/L). Additionally, LcGAD10s can be applied to a tofu fermentation system to achieve GABA conversion and achieved 14.9 mg/g of GABA conversion when added at 2 U/mL, which is higher than most of the commercial sufu and previous application reports, increasing its functional substances.

A systematic review about affinity tags for one-step purification and immobilization of recombinant proteins: integrated bioprocesses aiming both economic and environmental sustainability

The present study reviewed and discussed the promising affinity tags for one-step purification and immobilization of recombinant proteins. The approach used to structure this systematic review was The Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) methodology. The Scopus and Web of Science databases were used to perform the bibliographic survey by which 267 articles were selected. After the inclusion/exclusion criteria and the screening process, from 25 chosen documents, we identified 7 types of tags used in the last 10 years, carbohydrate-binding module tag (CBM), polyhistidine (His-tag), elastin-like polypeptides (ELPs), silaffin-3-derived pentalysine cluster (Sil3k tag), N-acetylmuramidase (AcmA tag), modified haloalkane dehalogenase (HaloTag®), and aldehyde from a lipase polypeptide (Aldehyde tag). The most used bacterial host for expressing the targeted protein was Escherichia coli and the most used expression vector was pET-28a. The results demonstrated two main immobilization and purification methods: the use of supports and the use of self-aggregating tags without the need of support, depending on the tag used. Besides, the chosen terminal for cloning the tag proved to be very important once it could alter enzyme activity. In conclusion, the best tag for protein one-step purification and immobilization was CBM tag, due to the eco-friendly supports that can be provided from industry wastes, the fast immobilization with high specificity, and the reduced cost of the process.

Changes in nutrient consumption patterns of Lactobacillus fermentum mediated by sodium lactate

BACKGROUND

During high-cell-density culture of Lactobacillus fermentum, the optimal pH is often maintained by adding NaOH. During cultivation at controlled pH, L. fermentum experiences osmotic stress due to the continuous accumulation of sodium lactate as a neutralizer product, affecting its survival in subsequent processing. The purpose of this study was to evaluate the nutrient consumption patterns of L. fermentum ATCC 14931 under sodium lactate stress and to screen nutrients that help it resist osmotic stress.

RESULTS

The consumption and consumption rates of amino acids, purines, pyrimidines, vitamins, and metal ions were analyzed in chemically defined media containing 0.13, 0.31, or 0.62 mm L^-1 sodium lactate. The highest consumption rates were found for arginine, guanine, folic acid, and Mn²⁺ , and the most consumed nutrients were glutamate + glutamine, guanine, ascorbic acid, and Na⁺ . Arginine 2.58 mm L^-1 , guanine 0.23 mm L^-1 , and Mn²⁺ 0.25 mm L^-1 were added to the medium at sodium lactate concentrations of 0.13 and 0.62 mm L^-1 , and arginine 2.58 mm L^-1 , guanine 0.26 mm L^-1 , and Mn²⁺ 0.25 mm L^-1 at a sodium lactate concentration of 0.31 mm L^-1 . The viable cell counts of L. fermentum ATCC 14931 were approximately 1.02-fold (P < 0.05) of the counts observed in control medium at all three concentrations of sodium lactate.

CONCLUSION

The present results suggest that certain nutrients accelerate the growth of L. fermentum under sodium lactate stress and enhance its resistance to this adverse condition. © 2022 Society of Chemical Industry.

Submerged and Solid-State Fermentation of Spirulina with Lactic Acid Bacteria Strains: Antimicrobial Properties and the Formation of Bioactive Compounds of Protein Origin

The aim of this study was to investigate the changes in bioactive compounds (L-glutamic acid (L-Glu), gamma-aminobutyric acid (GABA) and biogenic amines (BAs)) during the submerged (SMF) and solid-state (SSF) fermentation of Spirulina with lactobacilli strains (Lacticaseibacillus paracasei No. 244; Levilactobacillus brevis No. 173; Leuconostoc mesenteroides No. 225; Liquorilactobacillus uvarum No. 245). The antimicrobial properties of the untreated and fermented Spirulina against a variety of pathogenic and opportunistic strains were tested. The highest concentrations of L-Glu (3841 mg/kg) and GABA (2396 mg/kg) were found after 48 h of SSF with No. 173 and No. 244 strains, respectively. The LAB strain used for biotreatment and the process conditions, as well as the interaction of these factors, had statistically significant effects on the GABA concentration in Spirulina (p ≤ 0.001, p = 0.019 and p = 0.011, respectively). In all cases, the SSF of Spirulina had a higher total BA content than SMF. Most of the fermented Spirulina showed exceptional antimicrobial activity against Staphylococcus aureus but not against the other pathogenic bacteria. The ratios of BA/GABA and BA/L-Glu ranged from 0.5 to 62 and from 0.31 to 10.7, respectively. The GABA content was correlated with putrescine, cadaverine, histamine, tyramine, spermidine and spermine contents. The L-glutamic acid concentration showed positive moderate correlations with tryptamine, putrescine, spermidine and spermine. To summarize, while high concentrations of desirable compounds are formed during fermentation, the formation of non-desirable compounds (BAs) must also be considered due to the similar mechanism of their synthesis as well as the possibility of obtaining high concentrations in the end products.

Chromosomal editing of Corynebacterium glutamicum ATCC 13032 to produce gamma-aminobutyric acid

Corynebacterium glutamicum has been used as a sustainable microbial producer for various bioproducts using cheap biomass resources. In this study, a high GABA-producing C. glutamicum strain was constructed by chromosomal editing. Lactobacillus brevis-derived gadB2 was introduced into the chromosome of C. glutamicum ATCC 13032 to produce gamma-aminobutyric acid and simultaneously blocked the biosynthesis of lactate and acetate. GABA transport and degradation in C. glutamicum were also blocked to improve GABA production. As precursor of GABA, l-glutamic acid synthesis in C. glutamicum was enhanced by introducing E. coli gdhA encoding glutamic dehydrogenase, and the copy numbers of gdhA and gadB2 were also optimized for higher GABA production. The final C. glutamicum strain CGY705 could produce 33.17 g/L GABA from glucose in a 2.4-L bioreactor after 78 h fed-batch fermentation. Since all deletion and expression of genes were performed using chromosomal editing, fermentation of the GABA-producing strains constructed in this study does not need supplementation of any antibiotics and inducers. The strategy used in this study has potential value in the development of GABA-producing bacteria.

Changes in Spirulina's Physical and Chemical Properties during Submerged and Solid-State Lacto-Fermentation

The aim of this study was to select a lactic acid bacteria (LAB) strain for bio-conversion of Spirulina, a cyanobacteria ("blue-green algae"), into an ingredient with a high concentration of gamma-aminobutyric acid (GABA) for human and animal nutrition. For this purpose, ten different LAB strains and two different fermentation conditions (SMF (submerged) and SSF (solid state fermentation)) were tested. In addition, the concentrations of fatty acids (FA) and biogenic amines (BA) in Spirulina samples were evaluated. It was established that Spirulina is a suitable substrate for fermentation, and the lowest pH value (4.10) was obtained in the 48 h SSF with Levilactobacillus brevis. The main FA in Spirulina were methyl palmitate, methyl linoleate and gamma-linolenic acid methyl ester. Fermentation conditions were a key factor toward glutamic acid concentration in Spirulina, and the highest concentration of GABA (2395.9 mg/kg) was found in 48 h SSF with Lacticaseibacillus paracasei samples. However, a significant correlation was found between BA and GABA concentrations, and the main BA in fermented Spirulina samples were putrescine and spermidine. Finally, the samples in which the highest GABA concentrations were found also displayed the highest content of BA. For this reason, not only the concentration of functional compounds in the end-product must be controlled, but also non-desirable substances, because both of these compounds are produced through similar metabolic pathways of the decarboxylation of amino acids.

Effects of Tempeh Probiotics on Elderly With Cognitive Impairment

Introduction

Oral consumption of probiotics can alter Gut Microbiota by causing changes in the production of probiotic derivatives. Therefore, by utilizing Gut-Brain-Axis (GBA), probiotics could provide an opportunity for central nervous system (CNS) modulation, including cognitive function. Tempeh is a traditional Indonesian food rich in probiotics and beneficial for cognitive function. However, the type of probiotics that play a role in cognitive improvement and the number of probiotics needed for the benefits of increasing cognitive function was unknown.

Method

This experimental study involved a total of 93 subjects, divided into 3 groups: A, B and C/control (n: 33, 32, and 28), who were provided with probiotic supplementation isolated from tempeh for 12 weeks intervention. Inclusion criteria were age > 60 years, and memory impairment with the third repetition value of Word List Memory Immediate Recall (WLMIR) < 7. Subjects with diabetes were excluded. Cognitive function examinations were carried out before and after treatment. The tempeh-derived probiotics were prepared trough several processes. Genomic isolation, detection of GABA-encoding genes, and species identification using the 16S-rRNA gene encoding were performed.

Results

The probiotics isolate used in the intervention was identified as Limosilactobacillus fermentum. We assigned this isolate as L. fermentum A2.8. The presence of the gene encoding GABA was found on this isolate. There was an increase in the cognitive domains of memory, learning process, and verbal fluency (p < 0.05) in group A (probiotics at concentration of 10⁸ CFU/mL). Memory function, visuospatial, and verbal fluency improved (p < 0.05) in group B (probiotics at concentration of 10⁷ CFU/mL). Only an increase in the memory domain was observed in the control group. Improvement of the learning process occurred only in group A (p = 0.006).

Conclusion

Administration of probiotics derived from L. fermentum A2.8 increased the cognitive domains of memory, language and visuospatial function. However, probiotic supplementation at a concentration of 10⁸ CFU/mL was better in improving the learning process. This study succeeded in detecting Lactic Acid Bacterial isolates L. fermentum A2.8 that enclosed gene encoding glutamate decarboxylase (gad) which is involved in the synthesis of -aminobutyric acid (GABA), a neurotransmitter vital for cognitive function.

In Vitro Assessment of Bio-Functional Properties from Lactiplantibacillus plantarum Strains

In recent years, alongside the conventional screening procedures for the evaluation of probiotics for human usage, the pharmaceutical and food industries have encouraged scientific research towards the selection of new probiotic bacterial strains with particular functional features. Therefore, this study intended to explore novel functional properties of five Lactiplantibacillus plantarum strains isolated from bee bread. Specifically, antioxidant, antimicrobial and β-glucosidase activities, exopolysaccharides (EPS) production and the ability to synthesize γ-aminobutyric acid (GABA) were evaluated. The results demonstrated that the investigated L. plantarum strains were effective in inhibiting the growth of some human opportunistic pathogens in vitro (Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis, Enterococcus faecalis and Staphylococcus aureus). Moreover, the evaluation of antioxidant and β-glucosidase activity and of EPS and GABA production, revealed a different behavior among the strains, testifying how these properties are strongly strain-dependent. This suggests that a careful selection within a given species is important in order to identify appropriate strains for specific biotechnological applications. The results highlighted that the five strains of L. plantarum are promising candidates for application as dietary supplements in the human diet and as microbial cultures in specific food productions.

Expression, purification, and characterization of glutamate decarboxylase from human gut-originated Lactococcus garvieae MJF010

Human gut-originated lactic acid bacteria were cultivated, and high γ-aminobutyric acid (GABA)-producing Lactococcus garvieae MJF010 was identified. To date, despite the importance of GABA, no studies have investigated GABA-producing Lactococcus species, except for Lc. lactis. A recombinant glutamate decarboxylase of the strain MJF010 (rLgGad) was successfully expressed in Escherichia coli BL21(DE3) with a size of 53.9 kDa. rLgGad could produce GABA, which was verified using the silylation-derivative fragment ions of GABA. The purified rLgGad showed the highest GABA-producing activity at 35 °C and pH 5. rLgGad showed a melting temperature of 43.84 °C. At 30 °C, more than 80% of the activity was maintained even after 7 h; however, it rapidly decreased at 50 °C. The kinetic parameters, K_m, V_max, and k_cat, of rLgGad were 2.94 mM, 0.023 mM/min, and 12.3 min^- 1, respectively. The metal reagents of CaCl₂, MgCl₂, and ZnCl₂ significantly had positive effects on rLgGad activity. However, most coenzymes including pyridoxal 5'-phosphate showed no significant effects on enzyme activity. In conclusion, this is the first report of Gad from Lc. garvieae species and provides important enzymatic information related to GABA biosynthesis in the Lactococcus genus.

An Overview of Bioprocesses Employing Specifically Selected Microbial Catalysts for γ-Aminobutyric Acid Production

Gamma-aminobutyric acid (GABA) is an important chemical compound in the human brain. GABA acts as an inhibitory neurotransmitter by inducing hyperpolarization of cellular membranes. Usually, this pharmaceutically important compound is synthesized using a chemical process, but in this short overview we have only analysed microbial processes, which have been studied for the biosynthesis of this commercially important compound. The content of this article includes the following summarised information: the search for biological processes showed a number of lactic acid bacteria and certain species of fungi, which could be effectively used for the production of GABA. Strains found to possess GABA-producing pathways include Lactobacillus brevis CRL 1942, L. plantarum FNCC 260, Streptococcus salivarius subsp. thermophilus Y2, Bifidobacterium strains, Monascus spp., and Rhizopus spp. Each of these strains required specific growth conditions. However, several factors were common among these strains, such as the use of two main supplements in their fermentation medium—monosodium glutamate and pyridoxal phosphate—and maintaining an acidic pH. Optimization studies of GABA production were comprised of altering the media constituents, modifying growth conditions, types of cultivation system, and genetic manipulation. Some strains increased the production of GABA under anaerobic conditions. Genetic manipulation focused on silencing some genes or overexpression of gadB and gadC. The conclusion, based on the review of information available in published research, is that the targeted manipulation of selected microorganisms, as well as the culture conditions for an optimised bioprocess, should be adopted for an increased production of GABA to meet its increasing demand for food and pharmaceutical applications.

Design of a Full-Consensus Glutamate Decarboxylase and Its Application to GABA Biosynthesis

Glutamate decarboxylase (GAD) catalyses the decarboxylation of L-glutamate to gamma-aminobutyric acid (GABA). Improvement of the enzymatic properties of GAD is important for the low-cost synthesis of GABA. In this study, utilizing sequences of enzymes homologous with GAD from lactic acid bacteria, highly mutated GADs were designed using sequence-based protein design methods. Two mutated GADs, FcGAD and AncGAD, generated by full-consensus design and ancestral sequence reconstruction, had more desirable properties than native GADs. With respect to thermal stability, the half-life of the designed GADs was about 10 °C higher than that of native GAD. The productivity of FcGAD was considerably higher than those of known GADs; more than 250 mg/L of purified enzyme could be produced in the E. coli expression system. In a production test using 26.4 g of l-glutamate and 3.0 g of resting cells, 17.2 g of GABA could be prepared within one hour, without purification, in a one-pot synthesis.

Food-grade γ-aminobutyric acid production by immobilized glutamate decarboxylase from Lactobacillus plantarum in rice vinegar and monosodium glutamate system

OBJECTIVES

γ-amino butyric acid (GABA) is a non-protein amino acid, considered a potent bioactive compound. This study focused on biosynthesis of food-grade GABA by immobilized glutamate decarboxylase (GAD) from Lactobacillus plantarum in the rice vinegar and monosodium glutamate (MSG) reaction system.

RESULTS

The gene encoding glutamate decarboxylase (GadB) from L. plantarum has been heterologously expressed in Lactococcus lactis and biochemically characterized. Recombinant GadB existed as a homodimer, and displayed maximal activity at 40 °C and pH 5.0. The K_m value and catalytic efficiency (k_cat/K_m) of GadB for L-Glu was 22.33 mM and 62.4 mM^-1 min^-1, respectively, with a specific activity of 24.97 U/mg protein. Then, purified GadB was encapsulated in gellan gum beads. Compared to the free enzyme, immobilized GadB showed higher operational and storage stability. Finally, 9.82 to 21.48 g/L of GABA have been acquired by regulating the amounts of catalyst microspheres ranging from 0.5 to 0.8 g (wet weight) in 0.8 mL of the designed rice vinegar and MSG reaction system.

CONCLUSIONS

The method of production GABA by immobilized GadB microspheres mixed in the rice vinegar and MSG reaction system is introduced herein for the first time. Especially, the results obtained here meet the increased interest in the harnessing of biocatalyst to synthesize food-grade GABA.

Environmental Conditions Affecting GABA Production in Lactococcus lactis NCDO 2118

GABA (γ-aminobutyric acid) production has been widely described as an adaptive response to abiotic stress, allowing bacteria to survive in harsh environments. This work aimed to clarify and understand the relationship between GABA production and bacterial growth conditions, with particular reference to osmolarity. For this purpose, Lactococcus lactis NCDO 2118, a GABA-producing strain, was grown in glucose-supplemented chemically defined medium containing 34 mM L-glutamic acid, and different concentrations of salts (chloride, sulfate or phosphate ions) or polyols (sorbitol, glycerol). Unexpectedly, our data demonstrated that GABA production was not directly related to osmolarity. Chloride ions were the most significant factor influencing GABA yield in response to acidic stress while sulfate ions did not enhance GABA production. We demonstrated that the addition of chloride ions increased the glutamic acid decarboxylase (GAD) synthesis and the expression of the gadBC genes. Finally, under fed-batch conditions in a complex medium supplemented with 0.3 M NaCl and after a pH shift to 4.6, L. lactis NCDO 2118 was able to produce up to 413 mM GABA from 441 mM L-glutamic acid after only 56 h of culture, revealing the potential of L. lactis strains for intensive production of this bioactive molecule.

Immobilization and enzymatic properties of glutamate decarboxylase from Enterococcus faecium by affinity adsorption on regenerated chitin

Glutamate decarboxylase (GAD, EC 4.1.1.15) is an important enzyme in gamma-aminobutyric acid biosynthesis and DL-glutamic acid resolution. In this study, the Enterococcus faecium-derived GAD was successfully immobilized by regenerated chitin (RC) via specific adsorption of cellulose-binding domain (CBD). The optimal binding buffer was 20 mmol/L phosphate buffer saline (pH 8.0), and the RC binding capacity was 1.77 ± 0.11 mg_cbd-gad/g_rc under this condition. The ratio of wet RC and crude enzyme solution used for immobilization was recommended to 3:50 (g/mL). To evaluate the effect of RC immobilization on GAD, properties of the immobilize GAD (RC-CBD-GAD) were investigated. Results indicated RC-CBD-GAD was relatively stable at pH 4.4-5.6 and temperature - 20-40 °C, and the optimal reaction pH value and temperature were pH 4.8 and 50 °C, respectively. When it was reacted with 5 mmol/L of follow chemical reagents respectively, the activity of RC-CBD-GAD was hardly affected by EDTA, KCl, and NaCl, and significantly inactivated by AgNO₃, MnSO₄, MgSO₄, CuSO₄, ZnSO₄, FeCl₂, FeCl₃, AlCl₃, CaCl_2, and Pb(CH₃COO)₂. The apparent K_m and V_max were 28.35 mmol/L and 147.06 μmol/(g_RC-CBD-GAD·min), respectively. The optimum time for a batch of catalytic reaction without exogenous pH control was 2 h. Under this reaction time, RC-CBD-GAD had a good reusability with a half-life of 23 cycles, indicating that it was very attractive for GABA industry. As a novel, efficient, and green CBD binding carrier, RC provides an alternative way to protein immobilization.

Lactobacillus fermentum JX306 Restrain D-galactose-induced Oxidative Stress of Mice through its Antioxidant Activity

Oxidative stress-induced series of related degenerative diseases have received widespread attention. To screen new lactic acid bacteria (LAB) strains to resist oxidative stress, traditional Chinese fermented vegetables were used as a resource library to screen of LAB. The Lactobacillus fermentum JX306 strain, which showed high scavenging activity of DPPH free radical and hydrogen radical, and a strong lipid peroxidation inhibition rate in vitro was selected. L. fermentum JX306 was also examined for its antioxidant capacity in D-galactose-induced aging mice. The results showed that L. fermentum JX306 could significantly decrease malondialdehyde (MDA) levels and improve the activity of glutathione peroxidase (GSH-Px), and total antioxygenic capacity (TOC) in the serum, kidney, and liver. Meanwhile, the strain could remarkably upregulate the transcriptional level of the antioxidant-related enzyme genes, such as peroxiredoxin1 (Prdx1), glutathione reductase (Gsr), glutathione peroxidase (Gpx1), and thioredoxin reductase (TR3) encoding genes in the liver. Besides, histopathological observation proves that this probiotic strain could effectively inhibit oxidative damage to the liver and kidney in aging mice. Therefore, this unique antioxidant strain may have a high application value in the functional food industry and medicine industry.

Production of Gamma-Aminobutyric Acid from Lactic Acid Bacteria: A Systematic Review

Gamma-aminobutyric acid (GABA) is widely distributed in nature and considered a potent bioactive compound with numerous and important physiological functions, such as anti-hypertensive and antidepressant activities. There is an ever-growing demand for GABA production in recent years. Lactic acid bacteria (LAB) are one of the most important GABA producers because of their food-grade nature and potential of producing GABA-rich functional foods directly. In this paper, the GABA-producing LAB species, the biosynthesis pathway of GABA by LAB, and the research progress of glutamate decarboxylase (GAD), the key enzyme of GABA biosynthesis, were reviewed. Furthermore, GABA production enhancement strategies are reviewed, from optimization of culture conditions and genetic engineering to physiology-oriented engineering approaches and co-culture methods. The advances in both the molecular mechanisms of GABA biosynthesis and the technologies of synthetic biology and genetic engineering will promote GABA production of LAB to meet people’s demand for GABA. The aim of the review is to provide an insight of microbial engineering for improved production of GABA by LAB in the future.

A Brief Review on the Non-protein Amino Acid, Gamma-amino Butyric Acid (GABA): Its Production and Role in Microbes

Gamma-Aminobutyric acid (GABA) is a non-protein amino acid widely distributed in nature. It is produced through irreversible α-decarboxylation of glutamate by enzyme glutamate decarboxylase (GAD). GABA and GAD have been found in plants, animals, and microorganisms. GABA is distributed throughout the human body and it is involved in the regulation of cardiovascular conditions such as blood pressure and heart rate, and plays a role in the reduction of anxiety and pain. Although researchers had produced GABA by chemical method earlier it became less acceptable as it pollutes the environment. Researchers now use a more promising microbial method for the production of GABA. In the drug and food industry, demand for GABA is immense. So, large scale conversion of GABA by microbes has got much attention. So this review focuses on the isolation source, production, and functions of GABA in the microbial system. We also summarize the mechanism of action of GABA and its shunt pathway.