Diabetes has become the third most serious threat to human health, after cancer and cardiovascular disease. Notably, Lactobacillus brevis is the most common species of LAB that produces γ-aminobutyric acid (GABA). The aim of this study is to clarify the effect of time, strain types, antibiotic concentrations, different levels of pH, and intestinal juices in aerobic or anaerobic conditions and the effect of interactions between these factors on the potential properties of KLDS 1.0727 and KLDS 1.0373, furthermore, antagonistic activity against foodborne pathogens. Moreover, another aim is to study the capability of KLDS 1.0727 and KLDS 1.0373 strains as gad gene carriers to express GABA that reduce the risk of type 1 diabetes in C57BL/6 mice as diabetic models. The obtained results exhibited the surprising tolerance of Lactobacillus brevis strains in vitro digestion models mimicking the conditions of the gastrointestinal tract, further, large antagonistic activity against foodborne pathogeneses. In vivo results displayed the significant effect on glucose level reduction, blood plasma, and histological assays of mice organs. As recommended, the use of Lactobacillus brevis strains should be widely shared in the market as a natural source of GABA in pharmaceutical and food applications.

Lactobacillus plantarum KLDS1.0391 is a probiotic strain isolated from the traditional fermented dairy products and identified to produce bacteriocin against Gram-positive and Gram-negative bacteria. Previous studies showed that the strain has a high resistance to gastrointestinal stress and has a high adhesion ability to the intestinal epithelial cells (Caco-2). We reported the entire genome sequence of this strain, which contains a circular 2,886,607-bp chromosome and three circular plasmids. Genes, which are related to the biosynthesis of bacteriocins, the stress resistance to gastrointestinal tract environment and adhesive performance, were identified. Whole genome sequence of Lactobacillus plantarum KLDS1.0391 will be helpful for its applications in food industry.

Lactobacillus plantarum, a probiotic, has a high survival rate and high colonization ability in the gastrointestinal tract. Tolerance to the gastrointestinal environment and adhesion to intestinal epithelial cells by some Lactobacillus species (excluding L. plantarum) are related to luxS/AI-2. Here, the role of luxS in tolerance to simulated digestive juice (SDJ) and adhesion to Caco-2 cells by L. plantarum KLDS1.0391 (hereafter, KLDS1.0391) was investigated. The KLDS1.0391 luxS mutant strain was constructed by homologous recombination. When luxS was deleted, acid and bile salt tolerance and survival rates in SDJ significantly decreased (p < 0.05 for all). The ability of the luxS deletion strain to adhere to Caco-2 cells was markedly lower than that of the wild-type strain (p < 0.05). The ability of the luxS mutant strain to adhere (competition, exclusion, and displacement) to Escherichia coli ATCC 25922 was significantly lower than that of the wild-type strain (p < 0.05 for all). A significant decrease was noted only in the exclusion adhesion inhibition of the luxS mutant strain to Salmonella typhimurium ATCC 14028 (p < 0.05). These results indicate that the luxS gene plays an important role in the gastrointestinal environment tolerance and adhesion ability of KLDS1.0391.

Certain probiotic species of lactic acid bacteria, especially Lactobacillus plantarum, regulate bacteriocin synthesis through quorum sensing (QS) systems. In this study, we aimed to investigate the luxS-mediated molecular mechanisms of QS during bacteriocin synthesis by L. plantarum KLDS1.0391. In the absence of luxS, the ‘spot-on-the-lawn’ method showed that the bacteriocin production by L. plantarum KLDS1.0391 significantly decreased upon co-cultivation with L. helveticus KLDS1.9207 (P < 0.01) but did not change significantly when mono-cultivated. Furthermore, liquid chromatography-electrospray ionization tandem mass spectrometry analysis showed that, as a response to luxS deletion, L. plantarum KLDS1.0391 altered the expression level of proteins involved in carbohydrate metabolism, amino acid metabolism, fatty acid synthesis and metabolism, and the two-component regulatory system. In particular, the sensor histidine kinase AgrC (from the two-component system, LytTR family) was expressed differently between the luxS mutant and the wild-type strain during co-cultivation, whereas no significant differences in proteins related to bacteriocin biosynthesis were found upon mono-cultivation. In summary, we found that the production of bacteriocin was regulated by carbohydrate metabolism, amino acid metabolism, fatty acid synthesis and metabolism, and the two-component regulatory system. Furthermore, our results demonstrate the role of luxS-mediated molecular mechanisms in bacteriocin production.

A novel, Gram-stain-negative, aerobic, rod-shaped, non-motile and moderately halophilic bacterium, designated strain BJGMM-B45T , was isolated from a saline-alkali soil collected from Shandong Province, China. Growth of strain BJGMM-B45 T occurred at 10-45 6C (optimum, 30 6C) and pH 5.0-12.0 (optimum, pH 7.0) on Luria-Bertani agar medium with 1-20 % (w/v) NaCl (optimum, 7-10 %). The predominant respiratory quinone was Q-9. The major cellular fatty acids (.5 %) were C 18 : 1 v7c, , 1993). The genus Halomonas is the largest in the family Halomonadaceae. At the time of writing, the genus Halomonas includes more than 80 species with validly published names (http://www.bacterio.cict.fr/h/halomonas. html). Halomonas species are described as halotolerant or halophilic, Gram-negative, aerobic and rod-shaped bacteria (Holt et al., 2000;Dobson & Franzmann, 1996). Most of these species have been isolated from various saline habitats (Ventosa et al., 1998; Arahal et al., 2002b;Mata et al., 2002). In this study, we report the isolation and characterization of a novel, moderately halophilic bacterium, designated strain BJGMM-B45 T , which was isolated from a saline-alkali soil sample collected from Yellow River (Huanghe) Delta National Reserve Area (37 u 359-38 u 129 N 118 u 339-119 u 209 E) in Dongying City, Shandong Province, China.To isolate halophilic bacteria, a soil sample of approximately 1.0 g was cultivated in 0.9 % physiological saline solution at 30 u C with shaking at 200 r.p.m. for 24 h and then isolated using the 10-fold dilution-plating technique on Luria-Bertani (LB) agar medium with different NaCl concentrations (containing NaCl as indicated, 5 g yeast extract, 10 g tryptone and 15 g agar per litre deionized water, pH 7.0). After 48 h of incubation at 30 u C, a number of colonies had developed on LB agar medium with 10 % NaCl. After preliminary 16S rRNA gene sequence analysis, one of the cream-coloured colonies was selected and purified by repeated streaking. Cultures were stored at 280 u C in growth medium supplemented with 15 % glycerol. Unless specified otherwise, morphology and physiological studies were performed with cells grown on LB agar medium with 10 % NaCl at 30 u C and pH 7.0. Two reference strains, Halomonas cupida CGMCC 1.2312 T and Halomonas denitrificans DSM 18045 T , were obtainedThe GenBank/EMBL/DDBJ accession number for the 16S rRNA gene sequence of strain BJGMM-B45 T is JQ716246.