Γ-aminobutyric Acid Production Research Articles

Optimization of fermentation conditions for the production of γ-aminobutyric acid by Lactobacillus hilgardii GZ2 from traditional Chinese fermented beverage system.

γ-Aminobutyric acid (GABA) is a crucial neurotransmitter with wide application prospects. In this study, we focused on a GABA-producing strain from a traditional Chinese fermented beverage system. Among the six isolates, Lactobacillus hilgardii GZ2 exhibited the greatest ability to produce GABA in the traditional Chinese fermented beverage system. To increase GABA production, we optimized carbon sources, nitrogen sources, temperature, pH, and monosodium glutamate and glucose concentrations and conducted fed-batch fermentation. The best carbon and nitrogen sources for GABA production and cell growth were glucose, yeast extract and tryptone. Gradual increases in GABA were observed as the glucose and monosodium glutamate concentrations increased from 10g/L to 50g/L. During fed-batch fermentation, lactic acid was used to maintain the pH at 5.56, and after feeding with 0.03g/mL glucose and 0.4g/mL sodium glutamate for 72h, the GABA yield reached 239g/L. This novel high-GABA-producing strain holds great potential for the industrial production of GABA, as well as the development of health-promoting functional foods and medical fields.

Wine Barrel Biofilm as a Source of Yeasts with Non-Conventional Properties.

This study investigated the main microbial groups characterizing the interior surface of oak barrels from different years (1890, 1895, 1920, 1975, 2008) used in the production of vino cotto. The yeasts were characterized for the following properties: γ-aminobutyric acid (GABA) production, antioxidant activity, air-liquid interfacial biofilm formation, and anthocyanin adsorption capacity. Community-level physiological profile analysis revealed that the microbial communities inside the barrels used the tested carbon sources in different manners. The following yeast species were identified: Millerozyma farinosa, Zygosaccharomyces bisporus, Wickerhamiella versatilis, Zygosaccharomyces bailii, Starmerella lactis-condensi, and Zygosaccharomyces rouxii. All the strains were able to produce GABA, and S. lactis-condensi, Z. bisporus and Z. rouxii were the highest producers (more than 600 mg/L). The Z. rouxii and Z. bailii strains showed the highest antioxidant activity. Only seven strains out of ten M. farinosa formed air-liquid interfacial biofilm. None of the M. farinosa strains adsorbed anthocyanins on their cell wall. The other strains adsorbed anthocyanins in a strain-dependent way, and the highest adsorption was observed for the W. versatilis strains. The yeasts isolated in this study could be used to increase the functional properties and the quality of fermented foods and beverages.

Erratum for Konstanti et al., "Physiology of γ-aminobutyric acid production by Akkermansia muciniphila".

Erratum for Konstanti et al., "Physiology of γ-aminobutyric acid production by Akkermansia muciniphila".

Effect of Lactiplantibacillus plantarum cell-free supernatant on the physiology, quorum sensing, transcription, and enhanced GABA production of Enterococcus faecium

A co-culture strategy has been proposed for the production of desired products. However, the interaction effect on enhancing γ-aminobutyric acid (GABA) production requires further investigation. In this study, the mechanism by which Lactiplantibacillus plantarum BC112 cell-free supernatant (CFS) enhances GABA production in Enterococcus faecium AB157 was investigated, including physiological characteristics, quorum sensing (QS), and mRNA expression. The results showed CFS can significantly enhance the production of γ-aminobutyric acid (GABA) in E. faecium AB157, with a maximum increase of 4.6 times compared to the strain without CFS. CFS promoted the growth of E. faecium AB157, enhanced the activity of glutamate decarboxylase (GAD) and ATPase, and reduced the pH. The effect of CFS on QS was demonstrated through changes in Autoinducer-2 (AI-2) activity and luxS expression. Moreover, 16 amino acids were detected in CFS, with glutamic acid having the highest content. Additionally, 974 genes of E. faecium AB157 differed significantly in cultures with added CFS, which involved glycolytic, amino acid, and GABA biosynthetic pathways. Therefore, Lb. plantarum BC112 CFS enhances GABA production in E. faecium AB157 by affecting energy metabolism, the QS system, and the GABA biosynthesis system.

Screening and characterization of lactic acid bacteria and fermentation of gamma-aminobutyric acid-enriched bamboo shoots.

In order to produce fermented bamboo shoots with functional properties, two strains of lactic acid bacteria were selected for inoculation and fermentation. One strain, Lactiplantibacillus plantarum R1, exhibited prominent potential probiotic properties (including gastrointestinal condition tolerance, adhesion ability, antimicrobial ability, and antibiotic resistance), while the other, Levilactobacillus brevis R2, demonstrated the capability of high γ-aminobutyric acid (GABA) production (913.99 ± 14.2 mg/L). The synergistic inoculation of both strains during bamboo shoot fermentation led to a remarkable increase in GABA content (382.31 ± 12.17 mg/kg), surpassing that of naturally fermented bamboo shoots by more than 4.5 times and outperforming mono-inoculated fermentation. Simultaneously, the nitrite content was maintained at a safe level (5.96 ± 1.81 mg/kg). Besides, inoculated fermented bamboo shoots exhibited an increased crude fiber content (16.58 ± 0.04 g/100 g) and reduced fat content (0.39 ± 0.02 g/100 g). Sensory evaluation results indicated a high overall acceptability for the synergistically inoculated fermented bamboo shoots. This study may provide a strategy for the safe and rapid fermentation of bamboo shoots and lay the groundwork for the development of functional vegetable products enriched with GABA.

Enhanced fermentative γ-aminobutyric acid production by a metabolic engineered Corynebacterium glutamicum

Enhanced fermentative γ-aminobutyric acid production by a metabolic engineered Corynebacterium glutamicum

Decarboxylase activity of the non-starter lactic acid bacterium Loigolactobacillus rennini gives crack defects in Gouda cheese through the production of γ-aminobutyric acid.

Ten Gouda cheese wheels with an age of 31 weeks from six different batch productions were affected by a crack defect and displayed an unpleasant off-flavor. To unravel the causes of these defects, the concentrations of free amino acids, other organic acids, volatile organic compounds, and biogenic amines were quantified in zones around the cracks and in zones without cracks, and compared with those of similar Gouda cheeses without crack defect. The Gouda cheeses with cracks had a significantly different metabolome. The production of the non-proteinogenic amino acid γ-aminobutyric acid (GABA) could be unraveled as the key mechanism leading to crack formation, although the production of the biogenic amines cadaverine and putrescine contributed as well. High-throughput amplicon sequencing of the full-length 16S rRNA gene based on whole-community DNA revealed the presence of Loigolactobacillus rennini and Tetragenococcus halophilus as most abundant non-starter lactic acid bacteria in the zones with cracks. Shotgun metagenomic sequencing allowed to obtain a metagenome-assembled genome of both Loil. rennini and T. halophilus. However, only Loil. rennini contained genes necessary for the production of GABA, cadaverine, and putrescine. Metagenetics further revealed the brine and the rennet used during cheese manufacturing as the most plausible inoculation sources of both Loil. rennini and T. halophilus.IMPORTANCECrack defects in Gouda cheeses are still poorly understood, although they can lead to major economic losses in cheese companies. In this study, the bacterial cause of a crack defect in Gouda cheeses was identified, and the pathways involved in the crack formation were unraveled. Moreover, possible contamination sources were identified. The brine bath might be a major source of bacteria with the potential to deteriorate cheese quality, which suggests that cheese producers should regularly investigate the quality and microbial composition of their brines. This study illustrated how a multiphasic approach can understand and mitigate problems in a cheese company.

Antioxidant activity, GABA (γ-aminobutyric acid) production, and potential for colonization of Lactobacillus fermentum InaCC B1295 encapsulated with cellulose microfiber hydrogel from oil palm solid waste during storage

Lactobacillus fermentum InaCC B1295 is a probiotic bacterium that improves intestinal and immune systems, positively impacting human health. It produces various bioactive compounds, including bacteriocin, antioxidant enzymes, and gamma-aminobutyric acid (GABA), and colonizes the human gastrointestinal system. This study aimed to evaluate the antioxidant activity (IC50), GABA production, and colonization potential of L. fermentum InaCC B1295 with encapsulation by cellulose microfiber from oil palm solid waste (trunk, frond, leaf, and empty bunches) at room and refrigeration temperature with storage time 0, 14, and 28 days. The strain InaCC B1295 showed a high activity to scavenging ability against DPPH (1,1-diphenyl-2-picrylhydrazyl) for the treatment with encapsulation with oil palm empty bunches at refrigeration temperature after storage 14 days, which reached 88.56 ppm. Furthermore, L. fermentum InaCC B1295 produced GABA ranging from 0.435 mg/L to 2.215 mg/L. Lactobacillus fermentum InaCC B1295 encapsulated with oil palm leaf produced the most GABA at 0-day storage with a concentration of 2.215 mg/L and decreased during storage for all treatments. L. fermentum InaCC B1295 cells encapsulated in CMF hydrogel from empty oil palm fruit bunches had a lower autoaggregation value than free cells. The cells encapsulated with CMF hydrogel from oil palm empty bunches, on the other hand, had higher coaggregation and hydrophilicity values than the free cells (unencapsulated cells).

Efficient production of γ-aminobutyric acid using engineered Escherichia coli whole-cell catalyst

γ-Aminobutyric acid (GABA) has been widely used in the food, feed, pharmaceutical, and chemical industry fields. Previously, we developed a whole-cell catalyst capable of converting L-glutamate (L-Glu) into GABA by overexpressing the glutamate decarboxylase gene (gadz11) from Bacillus sp. Z11 in Escherichia coli BL21(DE3). However, to enhance cell permeability, a freeze-thaw treatment is required, and to enhance GADZ11 activity, pyridoxal 5′-phosphate (PLP) must be added to the reaction system. The aim of this study is to provide a more efficient approach for GABA production by engineering the recombinant E. coli above. First, the inducible expression conditions of the gadz11 in E. coli were optimized to 37 °C for 6 h. Next, an ideal engineered strain was produced via increasing cell permeability by overexpressing sulA and eliminating PLP dependence by constructing a self-sufficient system. Furthermore, an efficient whole-cell biocatalytic process was optimized. The optimal substrate concentration, cell density, and reaction temperature were 1.0 mol/L (the molecular ratio of L-Glu to L-monosodium glutamate (L-MSG) was 4:1), 15 and 37 °C, respectively. Finally, a whole-cell bioconversion procedure was performed in a 3-L bioreactor under optimal conditions. The strain could be reused for at least two cycles with GABA yield, productivity and conversion ratio of 206.2 g/L, 117.8 g/L/h and 100.0%, respectively. This is currently the highest GABA productivity from a mixture of L-Glu and L-MSG reported without the addition of cofactors or additional treatment of cells. This work demonstrates that the novel engineered E. coli strain has the potential for application in large-scale industrial GABA production.

Physiology of γ-aminobutyric acid production by Akkermansia muciniphila.

Gut bacteria hold the potential to produce a broad range of metabolites that can modulate human functions, including molecules with neuroactive potential. One such molecule is γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter of the central nervous system in animals. Metagenomic analyses suggest that the genomes of many gut bacteria encode glutamate decarboxylase (GAD), the enzyme that catalyzes GABA production. The genome of Akkermansia muciniphila, a mucin specialist and potential next-generation probiotic from the human gut, is predicted to encode GAD, suggesting a contributing role in GABA production in the human gut. In this study, A. muciniphila was grown in batch cultures with and without pH control. In both experiments, A. muciniphila was found to produce GABA as a response to acid (pH <5.5), although only when GABA precursors, either glutamate or glutamine, were present in the medium. Proteomic analysis comparing A. muciniphila grown with and without precursors at pH 4 did not show a difference in GAD expression, suggesting that it is expressed regardless of the presence of GABA precursors. To further investigate the function of A. muciniphila GAD, we heterologously expressed the gad gene (encoded by locus tag Amuc_0372) with a His tag in Escherichia coli and purified the GAD protein. Enzyme assays showed GAD activity in a pH range between 4 and 6, with the highest specific activity at pH 5 of 144 ± 16 µM GABA/min/mg. Overall, our results demonstrate the ability of A. muciniphila to produce GABA as an acid response and unravel the conditions under which GABA production in A. muciniphila occurs.IMPORTANCEAkkermansia muciniphila is considered to be a beneficial bacterium from the human gut, but the exact mechanisms by which A. muciniphila influences its host are not yet fully understood. To this end, it is important to identify which metabolites are produced and consumed by A. muciniphila that may contribute to a healthy gut. In the present study, we demonstrate the ability of A. muciniphila to produce γ-aminobutyric acid (GABA) when grown in an acidic environment, which often occurs in the gut. GABA is the major inhibitory neurotransmitter in the central nervous system and is present in the human gut. For this reason, it is considered an important bacterial metabolite. Our finding that A. muciniphila produces GABA in acidic environments adds to the growing body of understanding of its relationship with host health and provides an explanation on how it can survive acid stress in the human gut.

Spent coffee grounds as a potential culture medium for γ-aminobutyric acid (GABA) production by Levilactobacillus brevis PML1

This study aimed to investigate the Gamma-aminobutyric acid (GABA) production potential of Levilactobacillus brevis PML1 using an industrial waste-based culture medium. The optimization of GABA production was carried out in Spent Coffee Grounds (SCG) medium employing Response Surface Methodology (RSM). A Central Composite Design (CCD) was employed, revealing that the optimal SCG treatment conditions were as follows: 6% H2SO4 concentration, 120 min incubation, 0.14 mL Accellerase-1000 enzyme. High-performance chromatography analysis demonstrated a GABA yield of 492 mg/L after 48 h at 37 °C when supplemented with 3% monosodium glutamate. The antimicrobial activity assessment exhibited sensitivity towards Staphylococcus aureus among tested pathogenic bacteria. Scanning electron microscopy elucidated the antibacterial mechanism on Escherichia coli and S. aureus as representative strains. Furthermore, radical inhibitory activities were observed through DPPH assay recording a maximum inhibition rate of 13.15%, while FRAP assay indicated an antioxidant capacity of up to 0.419 mmol/L. Also, L. brevis demonstrated 53.40% cholesterol removal capability. Cytotoxic effects on human colon cancer cell lines Caco-2 were examined using MTT assay, yielding an IC50 value of approximately 3.25 g/mL for the extracts. In conclusion, this study highlights that SCG can serve as an affordable culture medium for efficient metabolite production.

Efficient Protein Expression and Biosynthetic Gene Cluster Regulation in Bacillus subtilis Driven by a T7-BOOST System.

Bacillus subtilis is a generally recognized as safe microorganism that is widely used for protein expression and chemical production, but has a limited number of genetic regulatory components compared with the Gram-negative model microorganism Escherichia coli. In this study, a two-module plug-and-play T7-based optimized output strategy for transcription (T7-BOOST) systems with low leakage expression and a wide dynamic range was constructed based on the inducible promoters Phy-spank and PxylA. The first T7 RNA polymerase-driven module was seamlessly integrated into the genome based on the CRISPR/Cpf1 system, while the second expression control module was introduced into low, medium, and high copy plasmids for characterization. As a proof of concept, the T7-BOOST systems were successfully employed for whole-cell catalysis production of γ-aminobutyric acid (109.8 g/L with a 98.0% conversion rate), expression of human αS1 casein and human lactoferrin, and regulation of exogenous lycopene biosynthetic gene cluster and endogenous riboflavin biosynthetic gene cluster. Overall, the T7-BOOST system serves as a stringent, controllable, and effective tool for regulating gene expression in B. subtilis.

Sodium butyrate alleviates fructose-induced non-alcoholic fatty liver disease by remodeling gut microbiota to promote γ-amino butyric acid production

Sodium butyrate (NaB) can regulate lipid metabolism and inhibit hepatic steatosis. This study aimed to investigate whether NaB can alleviate fructose-induced hepatic steatosis via remodeling the gut microbiota and evaluate the anti-fatty liver mechanisms. The results showed that NaB and NaB-remodeled gut microbiota significantly alleviated fructose-induced hepatic steatosis and increased plasma uric acid and fructose levels. Furthermore, both NaB and NaB-remodeled gut microbiota increased the abundance of Lactobacillus and altered the levels of plasma amino acids (upregulating gamma-amino butyric acid (GABA) and downregulating L-glutamic acid and L-arginine) in fructose-exposed mice. The correlation analysis showed that GABA levels positively correlated with Lactobacillus abundance, and increased GABA levels might promote the reduction of the hepatic triglyceride content. Further studies confirmed that GABA significantly reduced lipid deposition in mouse hepatocytes induced via fructose pretreatment in vitro. These findings suggested that NaB could ameliorate fructose-induced hepatic steatosis by regulating gut microbiota.

Oligofructose alone and in combination with 2'fucosyllactose induces physiologically relevant changes in γ-aminobutyric acid and organic acid production compared to sole 2'fucosyllactose supplementation: an in vitro study.

We explored the potential for the prebiotic oligofructose and prebiotic candidate 2'fucosyllactose, alone and in combination (50:50 blend) to induce physiologically relevant increases in neurotransmitter (γ-aminobutyric acid, serotonin, tryptophan, and dopamine) and organic acid (acetate, propionate, butyrate, lactate, and succinate) production as well as microbiome changes using anaerobic pH-controlled in vitro batch culture fermentations over 48h. Changes in organic acid and neurotransmitter production were assessed by gas chromatography and liquid chromatography and, bacterial enumeration using fluorescence in situ hybridization, respectively. Both oligofructose and oligofructose/2'fucosyllactose combination fermentations induced physiologically relevant concentrations of γ-aminobutyric acid, acetate, propionate, butyrate, and succinate at completion (all P ≤ .05). A high degree of heterogeneity was seen amongst donors in both neurotransmitter and organic acid production in sole 2'FL fermentations suggesting a large responder/nonresponder status exists. Large increases in Bifidobacterium, Lactobacillus, and Bacteroides numbers were detected in oligofructose fermentation, smallest increases being detected in 2'fucosyllactose fermentation. Bacterial numbers in the combined oligofructose/2'fucosyllactose fermentation were closer to that of sole oligofructose. Our results indicate that oligofructose and oligofructose/2'fucosyllactose in combination have the potential to induce physiologically relevant increases in γ-aminobutyric and organic acid production along with offsetting the heterogenicity seen in response to sole 2'fucosyllactose supplementation.

Development of a workflow for the selection, identification and optimization of lactic acid bacteria with high γ-aminobutyric acid production

Lactic acid bacteria produce γ-aminobutyric acid (GABA) as an acid stress response. GABA is a neurotransmitter that may improve sleep and resilience to mental stress. This study focused on the selection, identification and optimization of a bacterial strain with high GABA production, for development as a probiotic supplement. The scientific literature and an industry database were searched for probiotics and potential GABA producers. In silico screening was conducted to identify genes involved in GABA production. Subsequently, 17 candidates were screened for in vitro GABA production using thin layer chromatography, which identified three candidate probiotic strains Levilactobacillus brevis DSM 20054, Lactococcus lactis DS75843and Bifidobacterium adolescentis DSM 24849 as producing GABA. Two biosensors capable of detecting GABA were developed: 1. a transcription factor-based biosensor characterized by the interaction with the transcriptional regulator GabR was developed in Corynebacterium glutamicum; and 2. a growth factor-based biosensor was built in Escherichia coli, which used auxotrophic complementation by expressing 4-aminobutyrate transaminase (GABA-T) that transfers the GABA amino group to pyruvate, hereby forming alanine. Consequently, the feasibility of developing a workflow based on co-culture with producer strains and a biosensor was tested. The three GABA producers were identified and the biosensors were encapsulated in nanoliter reactors (NLRs) as alginate beads in defined gut-like conditions. The E. coli growth factor-based biosensor was able to detect changes in GABA concentrations in liquid culture and under gut-like conditions. L. brevis and L. lactis were successfully encapsulated in the NLRs and showed growth under miniaturized intestinal conditions.

Efficient biosynthesis of γ-aminobutyric acid by rationally engineering the catalytic pH range of a glutamate decarboxylase from Lactobacillus plantarum

γ-aminobutyric acid can be produced by a one-step enzymatic reaction catalyzed by glutamic acid decarboxylase. The reaction system is simple and environmentally friendly. However, the majority of GAD enzymes catalyze the reaction under acidic pH at a relatively narrow range. Thus, inorganic salts are usually needed to maintain the optimal catalytic environment, which adds additional components to the reaction system. In addition, the pH of solution will gradually rise along with the production of γ-aminobutyric acid, which is not conducive for GAD to function continuously. In this study, we cloned the glutamate decarboxylase LpGAD from a Lactobacillus plantarum capable of efficiently producing γ-aminobutyric acid, and rationally engineered the catalytic pH range of LpGAD based on surface charge. A triple point mutant LpGADS24R/D88R/Y309K was obtained from different combinations of 9 point mutations. The enzyme activity at pH 6.0 was 1.68 times of that of the wild type, suggesting the catalytic pH range of the mutant was widened, and the possible mechanism underpinning this increase was discussed through kinetic simulation. Furthermore, we overexpressed the Lpgad and LpgadS24R/D88R/Y309K genes in Corynebacterium glutamicum E01 and optimized the transformation conditions. An optimized whole cell transformation process was conducted under 40 ℃, cell mass (OD600) 20, 100 g/L l-glutamic acid substrate and 100 μmol/L pyridoxal 5-phosphate. The γ-aminobutyric acid titer of the recombinant strain reached 402.8 g/L in a fed-batch reaction carried out in a 5 L fermenter without adjusting pH, which was 1.63 times higher than that of the control. This study expanded the catalytic pH range of and increased the enzyme activity of LpGAD. The improved production efficiency of γ-aminobutyric acid may facilitate its large-scale production.

Metagenome-assembled genomes for biomarkers of bio-functionalities in Laal dahi, an Indian ethnic fermented milk product

Laal dahi is a sweetened and soft pudding-like fermented milk product of the Eastern regions of India, which has not been studied for its microbial community structures and health promoting functionality in terms of ‘omics’ approaches. We applied metagenomic and metagenomes-assembled genomes (MAGs) tools to decipher the biomarkers for genes encoding for different health promoting functionalities in laal dahi. Abundance of bacterial domains was observed with negligible presence of eukaryotes and viruses. Bacillota was the most abundant phylum with different bacterial species viz., Enterococcus italicus, Lactococcus raffinolactis, Lactobacillus helveticus, Bifidobacterium mongoliense, Hafnia alvei, Lactococcus lactis, Acetobacter okinawensis, Streptococcus thermophilus, Thermus thermophilus, Leuconostoc citreum, Leuconostoc pseudomesenteroides, Acetobacter orientalis, Lactobacillus gallinarum, Lactococcus chungangensis and Lactobacillus delbrueckii. Comparison of laal dahi microbiome with that of similar fermented milk products was also carried out after retrieving the metagenomic datasets from public databases. Significant abundance of Lb. helveticus, E. italicus, Lc. raffinolactis and Lc. lactis in laal dahi. Interestingly, Bifidobacterium mongoliense, Lb. gallinarum, Lc. chungangensis and Acetobacter okinawensis were only detected in laal dahi but Streptococcus infantarius, Lacticaseibacillus rhamnosus and Lb. johnsonii were absent. Reconstruction of putative single environment-specific genomes from metagenomes in addition to subsampling of the abundant species resulted in five high-quality MAGs identified as Lactobacillus delbrueckii, Lactobacillus helveticus, Lactococcus chungangensis, Lactococcus lactis and Streptococcus thermophilus. All MAGs showed the presence of various genes with several putative functions corresponding to different probiotic and prebiotic functions, short-chain fatty acids production, immunomodulation, antitumor genes, essential amino acid and vitamin biosynthesis. Genes for γ-Aminobutyric acid (GABA) production were only detected in MAG of Lactococcus lactis. Gene clusters for secondary metabolites (antimicrobial peptides) were detected in all MAGs except Lc. chungangensis. Additionally, detection of clustered regularly interspaced short palindromic repeats (CRISPR)-associated (Cas) elements was observed only in Lactobacillus delbrueckii and Streptococcus thermophilus. Annotation of several genes with potential health beneficial properties in all five MAGs may support the need to explore the culturability of these MAGs for future use in controlled fermentation of functional dairy products.

In vitro and in vivo evaluation of the safety of Levilactobacillus brevis CGMCC1.5954 with probiotic potential based on tri-generation whole genome sequencing and animal studies

In this study, the safety of Levilactobacillus brevis CGMCC1.5954 was evaluated, which has probiotic properties, through both in vitro methods such as antibiotic susceptibility testing, biogenic amine testing, and virulence gene analysis, and in vivo methods including biochemical testing, routine blood index testing, and bacterial displacement capacity analysis. The results of HPLC analysis revealed that during incubation, L. brevis CGMCC1.5954 did not secrete cadaverine, histamine, putrescine, or tyramine. It exhibited sensitivity to tetracyclines, macrolides, cephalosporins, β-lactamase inhibitor complex, and other antibiotics, but not to aminoglycosides and quinolones, which is consistent with the behavior of other lactic acid bacteria. Its genome encodes a total of 2314 genes, including 1743 proteins and 109 signal peptides. Notably, no virulence genes were found in this genome. Additionally, the gene encoding the production of γ-aminobutyric acid was found in it. In vivo experiments indicated that gavage feeding of L. brevis CGMCC1.5954 for 28 d had no significant effect on normal growth, blood hemoglobin level, erythrocytes, white blood cells, and other routine blood parameters in mice. Furthermore, there was no migration of it observed in the liver, kidney, spleen, or blood during the feeding trial, which indicated that it did not cause any infections. Moreover, H&E staining showed no evidence of lesion damage to the liver, kidney, or other organs. To sum up, L. brevis CGMCC1.5954 is considered safe for producing fermented foods, especially those that contain high levels of γ-aminobutyric acid.

γ-Aminobutyric acid produced by Levilactobacillus brevis using Chinese cabbage waste

To utilize Chinese cabbage waste (CCW) recovered from the pickle industry, a simple medium named Chinese cabbage medium (CCM) was developed for Levilactobacillus growth and γ-aminobutyric acid (GABA) production. The optimal medium compositions were 30% Chinese cabbage waste extracts (CCWE), 3% glucose, 0.25% yeast extract (YE), 0.25 X salts (0.25% sodium acetate, 0.1% sodium citrate, 0.1% ammonium sulfate, 0.005% magnesium sulfate and 0.0025% manganese sulfate), and initial pH 5.0 adjusted by HCl. L. brevis was incubated in this medium with 1% monosodium glutamate (MSG) at 30 °C for 24 h. Cell counts reached 4.16 × 109 CFU/ml, and the control results from MRS medium was 4.07 × 109 CFU/ml. GABA conversion rate at 18 h of this medium was 99.12%, higher than the MRS medium of 95.01%. Fructose and maltose were beneficial to the growth of L. brevis, but glucose was conducive to GABA synthesis. To obtain a high yield of GABA, CCM medium with 10% MSG was optimized by response surface methodology and resulted in 21.84% CCWE, 5.5% glucose, 4% YE, 1 X salt, 0.2% disodium phosphate, and initial pH of 4.5. GABA conversion rate reached 100% at 48 h with a final yield of 55.1 g/L.

Development of an oil-sealed anaerobic fermentation process for high production of γ-aminobutyric acid with Lactobacillus brevis isolated by directional colorimetric screening

γ-aminobutyric acid (GABA) is an important inhibitory neurotransmitter in the brain with many physiological functions. Therefore, this work establishes an efficient biosynthesis process to achieve the high production of food-grade GABA. Firstly, we adopted a directional colorimetric screening method and then obtained the strain Lactobacillus brevis (Lb. brevis) CGMCC 24975 with 22.61 g/L GABA in shake flasks, much higher than Lb. brevis ATCC 367 (3.07 g/L) due to its more efficient and stable expression of its glutamate decarboxylase (GAD) system. After exploring the effects of optimal fermentation conditions and oxygen on GABA production, we found that anaerobic fermentation could increase GABA production by up-regulating gad operon expression and activating GADase. Finally, we developed an oil-sealed anaerobic fermentation process with 157.90 g/L GABA in a 5 L bioreactor, which was 6.98-fold of that in shake flasks. This work includes a complete process from screening GABA-producing strains to developing efficient fermentation processes, laying the foundation for producing food-safe GABA.