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We have previously shown that the lactic acid bacterium (LAB) Enterococcus avium G-15 produces gamma-aminobutyric acid (GABA) from monosodium l-glutamate (Glu) at a hyper conversion rate. We have also found a gene cluster, designated as a gad cluster, that consists of four genes for the conversion of Glu to GABA, a Glu–GABA antiporter, and two transcriptional regulatory proteins, GadR1 and GadR2. The present study has been designed to investigate what characteristics of the GadG enzyme may contribute to the high production of GABA and how these two regulators play a role in high GABA productivity. The kinetic study showed that compared with E. coli glutamate decarboxylase (GAD) enzymes, GadG has relatively high Km (1.3–2.4 times) and kcat (1.3–1.6 times) values, indicating that although there are no remarkable differences in kinetic parameters between the three GAD enzymes, GadG may contribute to the high production of GABA in the presence of enough substrates. Further, the G-15 strain lacks the ornithine decarboxylase pathway-based acid resistance mechanism observed in some LAB strains, suggesting that the GAD-based acid resistance system is relatively important and may be vigorously employed in the G-15 strain. The molecular biological analysis of GadR1 revealed that the protein plays a role in GABA production as a transcriptional activator through an indirect pathway.

Oxidative stress from an excess of radical compounds generally impacts apoptosis and inflammation. The use of probiotics, therefore, has emerged as a favorable tool to suppress the formation of reactive oxygen species. In the present study, we investigated the antioxidant activity of plant-derived Lactiplantibacillus (L.) plantarum MSC-5T fermented in Eriobotrya japonica (EJ) aqueous extract. In the in vitro study, the extract fermented with the MSC-5T strain markedly decreased the cell death of H2O2-induced HEK293 cells. In addition, the fermented extract showed a protective effect against fungal toxin ochratoxin A (OTA) and citrinin (CTN). Regarding the evaluation of glutathione homeostasis, it can be clearly seen that pretreatment of HEK293 cells with fermented EJ extract greatly increased glutathione (GSH) levels, while unfermented extract did not affect the cellular GSH content. Furthermore, we identified a bioactive compound as pyrocatechol, which displayed significant antioxidation activity. The extract fermented for 48 h with the MSC-5T strain in EJ extract produces 167.4 μg/mL pyrocatechol.

We previously found that fermented extract of Dendrobium officinale using Lactobacillus plantarum GT-17F has a stronger antioxidant effect, especially in free radical scavenging. The result provided a basis for further studies to evaluate the effectiveness of fermented D. officinale in preventing UV-mediated damage and photoaging in humans. Therefore, in this study, we aimed to assess the anti-aging efficacy of D. officinale fermented with GT-17F strain in a clinical trial, which was conducted as a double-blind, placebo-controlled, randomized parallel-group comparative study with 99 volunteers with visible wrinkles. During the study, subjects were instructed to apply one pump of each essence, which contains fermented, unfermented, or no D. officinale extract, evenly to their face, both in the morning and evening, following their cleansing routine. At 28 days post-treatment, compared to baseline, subjects in the fermented extract group demonstrated significant improvements in stratum corneum water content, skin elasticity, skin glossiness, wrinkle area and ratio, erythema area, and erythema area ratio. In contrast, the unfermented extract group showed a significant difference only in improving erythema index levels in the skin. This comprehensive study has rigorously investigated the anti-aging effects of D. officinale and its fermented version on human skin, highlighting a notable contribution to dermatological research.

In the present study, the effect of PLA on a periodontic pathogen, Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans), the biofilm, and virulence-related genes was investigated. We confirmed that two lactic acid bacteria (LAB) strains isolated from plant sources, Lactiplantibacillus plantarum MSC-C2 and Pediococcus pentosaceus K40, secrete PLA into the de Man, Rogosa & Sharpe (MRS) broth when supplemented with phenyl pyruvic acid (PPA) as a precursor to PLA. Moreover, PLA was generated in the fermentation broths of two medicinal plant extracts, Paeonia lactiflora Pall (PR) and Carthamus tinctorius (CT), when used by each LAB strain and each extract supplemented with PPA. We determined that the minimum inhibitory concentration (MIC) of PLA against A. actinomycetemcomitans was 20 mM. PLA significantly decreased biofilm formation and suppressed the transcription of pgA, ltxA, and cdtB genes, which encode the poly-N-acetylglucosamine (PGA) polysaccharide of biofilm matrix and exotoxins leukotoxin and cytolethal distending toxin (CDT), respectively. The PLA produced by the MSC-C2 and K40 strains was increased several times by the addition of PPA to the MRS broth. The anti-biofilm effect of the extracts from the fermentation broth was proportional to the increasing PLA concentration, while a cumulatively higher effect than that of PLA alone suggested a combinational effect of PLA and the other metabolites, such as lactic acid (LA). Among the two medicinal plants, PLA, produced after the addition of PPA, was higher in PR extract in case of both the LAB strains. PLA production by the MSC-C2 strain in the PR extract reached 4.8 ± 0.23 mM, which was obviously higher than that in the MRS broth (3.88 ± 0.12 mM) supplemented with 1 mg/ml PPA. The activity to inhibit biofilm formation in the fermented PR extract was clearly high. PLA formed in the fermented PR extract downregulated the dispersin B encoding the dspB gene together with pgA, ltxA, and cdtB. In conclusion, this study shows a promising activity of PLA against the A. actinomycetemcomitans biofilm and virulence genes. In addition, the combinational effect of PLA and the medicinal plant extract can be achieved by fermentation with a specific plant-derived LAB strain.

Lactic acid bacterial (LAB) fermentation of functional amino acids using fruit juices as a cultivation medium is not well-documented. In the present study, we successfully isolated a high ornithine- and citrulline-producing Lactococcus lactis strain, designated MSC-3G, from sugarcane and investigated the ornithine and citrulline production profile using various fruit juices as a cultivation medium. Among fruit juices, pineapple juice exhibited the highest potentiality to initiate ornithine production (56 mM), while the highest citrulline yield was obtained during lime juice cultivation (34.5 mM). Under the optimal cultivation condition, the highest yield of ornithine and citrulline in pineapple juice reached 98.9 ± 2.2 mM and 211.1 ± 35.7 mM, respectively, both of which were significantly higher than that in the well-known industrial strain of Corynebacterium (C.) glutamicum. Additionally, citrulline production was dependent on oxygen supplementation and increased twofold when grown aerobically. Whole genome sequencing showed that the MSC-3G genome possesses the arginine deiminase (ADI) gene cluster arcABD1C1C2TD2. The results of the ADI pathway enzyme activities of MSC-3G showed a significant increase in arginine deiminase activity, while ornithine carbamoyl transferase activity was decreased, which in turn indicates the high citrulline-accumulation ability of MSC-3G when cultivated in pineapple juice.