Draft Genome Sequence of Bifidobacterium adolescentis 4-2, Isolated from Healthy Human Feces

Bifidobacterium adolescentis 4-2 was isolated from healthy human feces. Here, we report a draft genome sequence of this bacterium, which may clarify the functionality of gut microbiota-brain communication. The draft genome comprises 2.39 Mb, with an average G+C content of 59.2% and 2,028 coding DNA sequences. An operon for GABA biosynthesis was observed in the draft genome.

Molecular Analysis of Glutamate Decarboxylases in Enterococcus avium

Enterococcus avium (E. avium) is a common bacterium inhabiting the intestines of humans and other animals. Most strains of this species can produce gamma-aminobutyric acid (GABA) via the glutamate decarboxylase (GAD) system, but the presence and genetic organization of their GAD systems are poorly characterized. In this study, our bioinformatics analyses showed that the GAD system in E. avium strains was generally encoded by three gadB genes (gadB1, gadB2, and gadB3), together with an antiporter gene (gadC) and regulator gene (gadR), and these genes are organized in a cluster. This finding contrasts with that for other lactic acid bacteria. E. avium SDMCC050406, a GABA producer isolated from human feces, was employed to investigate the contribution of the three gadB genes to GABA biosynthesis. The results showed that the relative expression level of gadB3 was higher than those of gadB1 and gadB2 in the exponential growth and stationary phases, and this was accompanied by the synchronous transcription of gadC. After heterologous expression of the three gadB genes in Escherichia coli BL21 (DE3), the Km value of the purified GAD3 was 4.26 ± 0.48 mM, a value lower than those of the purified GAD1 and GAD2. Moreover, gadB3 gene inactivation caused decreased GABA production, accompanied by a reduction in resistance to acid stress. These results indicated that gadB3 plays a crucial role in GABA biosynthesis and this property endowed the strain with acid tolerance. Our findings provided insights into how E. avium strains survive the acidic environments of fermented foods and throughout transit through the stomach and gut while maintaining cell viability.

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.

Regulation of Heat Shock Factor Pathways by γ-aminobutyric Acid (GABA) Associated with Thermotolerance of Creeping Bentgrass

Activation and enhancement of heat shock factor (HSF) pathways are important adaptive responses to heat stress in plants. The γ-aminobutyric acid (GABA) plays an important role in regulating heat tolerance, but it is unclear whether GABA-induced thermotolerance is associated with activation of HSF pathways in plants. In this study, the changes of endogenous GABA level affecting physiological responses and genes involved in HSF pathways were investigated in creeping bentgrass during heat stress. The increase in endogenous GABA content induced by exogenous application of GABA effectively alleviated heat damage, as reflected by higher leaf relative water content, cell membrane stability, photosynthesis, and lower oxidative damage. Contrarily, the inhibition of GABA accumulation by the application of GABA biosynthesis inhibitor further aggravated heat damage. Transcriptional analyses showed that exogenous GABA could significantly upregulate transcript levels of genes encoding heat shock factor HSFs (HSFA-6a, HSFA-2c, and HSFB-2b), heat shock proteins (HSP17.8, HSP26.7, HSP70, and HSP90.1-b1), and ascorbate peroxidase 3 (APX3), whereas the inhibition of GABA biosynthesis depressed these genes expression under heat stress. Our results indicate GABA regulates thermotolerance associated with activation and enhancement of HSF pathways in creeping bentgrass.

Cloning and Characterization of a cDNA Encoding Calcium/Calmodulin-Dependent Glutamate Decarboxylase from Scutellaria Baicalensis

Gamma-aminobutyric acid (GABA), synthesized by glutamate decarboxylase (GAD), plays an important role in plants. To study the molecular mechanism of GAD regulation and to examine the levels of GABA in Scutellaria baicalensis, we isolated cDNA clones (SbGAD1 and 2) encoding GAD from S. baicalensis. The open reading frames of SbGAD1 and 2 were 1,503 and 1,494 bp long and had 450 and 497 amino acid residues, respectively. Quantitative real-time RT-PCR analysis was performed to show the variation of transcript levels among different organs of S. baicalensis. Transcript levels of SbGAD1 and 2 were highest in the root and flower, respectively. The GABA content of different parts (ranked in descending order) was as follows: leaf > flower > stem > root. We concluded that the expression pattern of SbGAD1 and 2 did not match the accumulation pattern of GABA in different organs. We presume that GABA biosynthesis might be more controlled by SbGAD2 than SbGAD1. These data will aid in future studies that seek to understand the mechanisms underlying GABA biosynthesis, an important amino acid that is synthesized by the GAD enzyme. To explain adequately the GABA biosynthesis mechanisms in S. baicalensis, the enzyme activities of SbGAD1 and 2 should be determined in the near future.