• Proceedings of the Korean Society of Plant Pathology Conference
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• 2003.10a
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• pp.66.1-66
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• 2003

The aim of this study was to characterize the interactions of rice and Burkholderia glumae, a causal agent of bacterial grain rot of rice, at molecular levels using whole genomic sequences and to identify genes important for pathogenicity and symptom development. To do these, we sequenced whole genome of the bacterium and constructed cosmid clone profiles. We generated pools of mutants using various transposons and determined mutation sites by sequencing rescued plasmids. We focused on studying toxoflavin biosynthetic genes, quorum sensing regulation, and Hrp type III protein secretion systems. We found that two possible operons consisting of five genes are involved in toxoflavin biosynthesis and their expression is regulated by quorum sensing and LysR-type regulator, ToxR. We have isolated the nn PAI of B. glumae and characterized by mutational analyses. The hrp cluster resembled most the putative Type III secretion systems of B. pseudomallei, which is the causative agent of melioidosis, a serious disease of man and animals. The Hrp PAI core region showed high similarity to that of Ralstonia solanacearum and Xanthomonas campestris, however some aspects were dissimilar.

• Journal of Microbiology and Biotechnology
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• v.26 no.9
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• pp.1566-1569
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• 2016

Three flavonoids were isolated from dried flowers of Sophora japonica using repetitive column chromatography and high-performance liquid chromatography. The flavonoids were identified as rutin (1), quercetin-3'-O-methyl-3-O-α-ʟ-rhamnopyranosyl(1 → 6)-β-ᴅ-glucopyranoside (2), and quercetin (3) on the basis of spectroscopic analysis and comparison of values reported in the literature. These compounds inhibited the action of sortase A (SrtA) from Streptococcus mutans, a primary etiologic agent of human dental caries. The onset and magnitude of inhibition of saliva-induced aggregation of S. mutans treated with compound 1 was comparable to that of untreated S. mutans with a deletion of the srtA gene.

• Journal of Microbiology and Biotechnology
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• v.26 no.9
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• pp.1579-1585
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• 2016

Sugar esters are valuable compounds composed of various sugars and fatty acids that can be used as antibacterial agents and emulsifiers in toothpaste and canned foods. For example, fructose fatty acid esters suppress growth of Streptococcus mutans, a typical pathogenic bacterium causing dental caries. In this study, fructose laurate ester was chosen as a target material and was synthesized by a transesterification reaction using Candida antarctica lipase B. We performed a solvent screening experiment and found that a t-butanol/dimethyl sulfoxide mixture was the best solvent to dissolve fructose and methyl laurate. Fructose laurate was synthesized by transesterification of fructose (100 mM) with methyl laurate (30 mM) in t-butanol containing 20% dimethyl sulfoxide. The conversion yield was about 90%, which was calculated based on the quantity of methyl laurate using high-performance liquid chromatography. Fructose monolaurate (M_r 361) was detected in the reaction mixture by high-resolution mass spectrometry. The inhibitory effect of fructose laurate on growth of oral or food spoilage microorganisms, including S. mutans, Bacillus coagulans, and Geobacillus stearothermophilus, was evaluated.

• Journal of Microbiology and Biotechnology
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• v.16 no.2
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• pp.286-290
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• 2006

A genomic library of Streptococcus vestibularis ATCC49124 was constructed in an E. coli plasmid vector, and the urease-positive transformants harboring the urease gene cluster were isolated on Christensen-urea agar plates. The minimal DNA region required for urease activity was located in a 5.6 kb DNA fragment, and a DNA sequence analysis revealed the presence of a partial ureI gene and seven complete open reading frames, corresponding to ureA, B, C, E, F, G, and D, respectively. The nucleotide sequence over the entire ure gene cluster and 3'-end flanking region of S. vestibularis was up to 95% identical to that of S. salivarius, another closely related oral bacterium, and S. thermophilus, isolated from dairy products. The predicted amino acid sequences for the structural peptides were 98-100% identical to the corresponding peptides in S. salivarius and S. thermophilus, respectively, whereas those for the accessory proteins were 96-100% identical. The recombinant E. coli strain containing the S. vestibularis ure gene cluster expressed a high level of the functional urease holoenzyme when grown in a medium supplemented with 1 mM nickel chloride. The enzyme was purified over 49-fold by using DEAE-Sepharose FF, Superdex HR 200, and Mono-Q HR 5/5 column chromatography. The specific activity of the purified enzyme was 2,019 U/mg, and the Michaelis constant ($K_{m}$) of the enzyme was estimated to be 1.4 mM urea. A Superose 6HR gel filtration chromatography study demonstrated that the native molecular weight was about 196 kDa.

• Journal of Microbiology and Biotechnology
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• v.18 no.5
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• pp.845-851
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• 2008

TolC is an outer membrane porin protein and an essential component of drug efflux and type-I secretion systems in Gram-negative bacteria. TolC comprises a periplasmic $\alpha$-helical barrel domain and a membrane-embedded $\beta$-barrel domain. TdeA, a functional and structural homolog of TolC, is required for toxin and drug export in the pathogenic oral bacterium Actinobacillus actinomycetemcomitans. Here, we report the expression of the periplasmic domain of TdeA as a soluble protein by substitution of the membrane-embedded domain with short linkers, which enabled us to purify the protein in the absence of detergent. We confirmed the structural integrity of the TdeA periplasmic domain by size-exclusion chromatography, circular dichroism spectroscopy, and electron microscopy, which together showed that the periplasmic domain of the TolC protein family fold correctly on its own. We further demonstrated that the periplasmic domain of TdeA interacts with peptidoglycans of the bacterial cell wall, which supports the idea that completely folded TolC family proteins traverse the peptidoglycan layer to interact with inner membrane transporters.

• Journal of Microbiology and Biotechnology
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• v.33 no.6
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• pp.823-830
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• 2023

Lactococcus lactis is a lactic acid bacterium and used in the dairy food industry. The ameliorating effects of Lactobacillus species on atopic dermatitis (AD) have been extensively studied, but the specific effect of L. lactis strains has not yet been investigated. In this study, the efficacy of L. lactis LB 1022, isolated from natural cheese, was evaluated using RAW 264.7, HMC-1 and HaCaT cell lines and an ovalbumin-sensitized AD mouse model. L. lactis LB 1022 exhibited nitric oxide suppression and anti-allergy and anti-inflammatory activity in vitro. Oral administration of L. lactis LB 1022 to AD mice significantly reduced the levels of IgE, mast cells, and eosinophils, and a range of T cell-mediated T helper Th1, Th2, and Th17-type cytokines under interleukin (IL)-10, transforming growth factor-β (TGF-β), thymus and activation-regulated chemokine (TARC), and thymic stromal lymphopoietin (TSLP). In addition, L. lactis LB 1022 treatment increased the concentration of short-chain fatty acids. Overall, L. lactis LB 1022 significantly modulated AD-like symptoms by altering metabolites and the immune response, illustrating its potential as candidate for use in functional food supplements to alleviate AD.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.6
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• pp.892-897
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• 2013

We investigated the acute toxicity from a single dose of crude anti-fungal compounds produced by Lactobacillus plantarum AF1, a lactic acid bacterium isolated from kimchi, on ICR male and female mice in vivo. The test article was orally administered once to both sexes of mice. The mortality rate, clinical findings, autopsy findings, and body weight changes were monitored daily for 14 days. In the oral acute toxicity test, male and female mice were gavaged with four doses (5, 50, 300 or 2,000 mg/kg) of the crude anti-fungal compounds. The oral $LD_{50}$ of the crude anti-fungal compounds was higher than 2,000 mg/kg. No significant changes in general conditions, body weights, clinical signs, or appearance of gross lesions were observed. In conclusion, our results suggest a low toxicity and no-adverse-effects from crude anti-fungal compounds produced by Lactobacillus plantarum AF1 up to 2,000 mg/kg via the oral route.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.4
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• pp.600-607
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• 2013

This study was performed to investigate the repeated-dose toxicity of Leuconostoc citreum GR1 (Leuc. citreum GR1), a lactic acid bacterium isolated from kimchi, in male and female rats. Sprague-Dawley male and female rats were divided into four group (ten animals in each group) and Leuc. citreum GR1 was administered daily by gavage to rats at dosage levels of 0, 500, 1,000, or 2,000 mg/kg/day for four weeks. There were no bacterial-related deaths or abnormal clinical signs in either gender of rats during the observation period. Furthermore, no differences were found between the control and treatment groups in terms of body weight, food intake, and water consumption. Hematological parameters, serum biochemical analysis, and histopathological examination also showed insignificant dose-dependent alterations. There were also no alterations in organ weights upon administration of Leuc. citreum GR1 alone. These results suggest the oral application of Leuc. citreum GR1, up to a dosage level of 2,000 mg/kg, causes no adverse effects in both male and female rats.

• Food Science and Preservation
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• v.19 no.2
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• pp.315-321
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• 2012

The $in$ $vivo$ single-dose acute toxicity of $Lactobacillus$ $plantarum$ AF1, a lactic acid bacterium isolated from kimchi, in ICR male and female mice was investigated. The test article was intraperitoneally or orally administered once to both sexes of mice. The motalites, clinical findings, autopsy findings, and body weight changes were monitored daily for 14 days. In the oral acute toxicity test, the male and female mice were gavaged with four doses (5.0, 2.5, 1.25 and 0.625 g/kg) of $Lb.$ $plantarum$ AF1. The oral $LD_{50}$ of the $Lb.$ $plantarum$ AF1 was considered higher than 5.0 g/kg. In the intraperitoneal acute toxicity test, mice were injected intraperitoneally with dosages of 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3 and 2.5 g/kg. The intraperitoneal 50% lethal dose ($LD_{50}$) of the $Lb.$ $plantarum$ AF1 was >2.5 g/kg in the male and female mice. No significant changes in the general conditions, body weights, clinical signs, and gross lesions were observed in both sexes of mice to which $Lb.$ $plantarum$ AF1 was administered intraperitoneally or orally. The results suggest that the no-adverse-effect level of $Lb.$ $plantarum$ AF1 is estimated to be more than 5.0 g/kg in the oral route and 2.5 g/kg in the intraperitoneal route.

• Food Science and Preservation
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• v.20 no.3
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• pp.394-403
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• 2013

This study was performed to investigate the four-week repeated-dose toxicity of the crude antifungal compounds produced by Lactobacillus plantarum AF1 (Lb. plantarum AF1), a lactic acid bacterium isolated from kimchi, in male and female rats. Sprague-Dawley male and female rats were divided into four groups, with 10 animals in each group. The test article was administered once daily by gavage to rats at dosage levels of 0, 500, 1,000, and 2,000 mg/kg/day for four weeks. There were no test-article-related deaths or abnormal clinical signs in both the male and female rats during the observation period. Furthermore, no differences in the body weight changes, food intake and water consumption levels of the control and treatment groups were found. The hematological parameters, serum biochemical analysis results, histopathological examination results and all other findings also showed no significant or dose-dependent changes. There were also no changes in the organ weights upon the administration of the crude antifungal compounds produced by Lb. plantarum AF1. These results suggest that the oral administration of the crude antifungal compounds produced by Lb. plantarum AF1 had no adverse effects up to a dosage level of 2,000 mg/kg in both male and female rats.