High-level production of γ-aminobutyric acid via efficient co-expression of the key genes of glutamate decarboxylase system in Escherichia coli

Advances in engineering and applications of microbial glutamate decarboxylases for gamma-aminobutyric acid production

Gamma-aminobutyric acid (GABA) is a key neurotransmitter with significant health benefits, including anxiolytic and anti-hypertensive effects, and potential use in biodegradable material synthesis. The increasing market demand for GABA has intensified the search for cost-effective production methods. The key enzyme involved in GABA production is glutamate decarboxylase (GAD), which catalyzes the conversion of L-glutamate to GABA. GAD plays a central role in various production approaches, such as enzyme-based catalysis, whole-cell catalysis, and microbial fermentation. Although microbial GADs are preferred for their high catalytic activity, their low pH and thermal stability present significant challenges for large-scale GABA production. Wild-type GADs typically have an optimal pH range of 4-5, and their activity sharply declines as the pH increases, thereby reducing production efficiency. Furthermore, GADs' poor thermal stability makes them vulnerable to temperature fluctuations during industrial processes, further limiting GABA production. Recent research has focused on engineering GAD variants with improved stability and performance through rational design, directed evolution, and semi rational approaches. These advancements not only expand the potential applications of GAD in biocatalysis but also offer promising solutions for sustainable GABA production. This paper provides an in-depth review of the engineering of GADs, applications of GAD in GABA production, and strategies to overcome limitations, offering a comprehensive overview of the current state and future prospects of GAD modification in enhancing GABA production.

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.

Whole-genome analysis, evaluation and regulation of in vitro and in vivo GABA production from Levilactobacillus brevis YSJ3

Gamma-aminobutyric acid (GABA) produced by lactic acid bacteria (LAB) is safe and has several health benefits. Levilactobacillus brevis YSJ3 was selected from 110 LAB. It exhibited the highest in vitro GABA production level of 970.10 μg/mL. Whole-genome analysis revealed that L. brevis YSJ3 contained gadR, gadC, gadB and gadA. Furthermore, the Luedeking-Piret model was fitted, which indicated that GABA production was divided into three stages. The gadR 0079, gadC 0080, and gadB 0081 were confirmed to promote GABA synthesis. Moreover, 55 metabolites, particularly those involved in arginine metabolism, were significantly different at 6 and 20 h of cultivation. Notably, L. brevis YSJ3 significantly improved sleep in mice and increased GABA levels in the mice's gut compared with the control group. This suggests that the oral administration of L. brevis YSJ3 improves sleep quality, probably by increasing intestinal GABA levels. Overall, L. brevis YSJ3 was confirmed as a GABA-producing strain in vitro and in vivo, making it a promising probiotic candidate for its application in food and medicine.

Gut commensal Christensenella minuta modulates host metabolism via acylated secondary bile acids

A strong correlation between gut microbes and host health has been observed in numerous gut metagenomic cohort studies. However, the underlying mechanisms governing host-microbe interactions in the gut remain largely unknown. Here we report that the gut commensal Christensenella minuta modulates host metabolism by generating a previously undescribed class of secondary bile acids with 3-O-acylation substitution that inhibit the intestinal farnesoid X receptor. Administration of C. minuta alleviated features of metabolic disease in high fat diet-induced obese mice associated with a significant increase in these acylated bile acids, which we refer to as 3-O-acyl-cholic acids. Specific knockout of intestinal farnesoid X receptor in mice counteracted the beneficial effects observed in their wild-type counterparts. Finally, we showed that 3-O-acyl-CAs were prevalent in healthy humans but significantly depleted in patients with type 2 diabetes. Our findings indicate a role for C. minuta and acylated bile acids in metabolic diseases.