Do-Won Jeong

Cloning and characterization of the gene encoding phosphoketolase in Leuconostoc mesenteroides isolated from kimchi

The gene encoding phosphoketolase, which is 2749 bp long and contains 814 amino acid polypeptides with a total molecular mass of 91.9 kDa, was cloned from Leuconostoc mesenteroides C7 (LMC7) and expressed in Escherichia coli. It exhibited a homology of >58% with phosphoketolases from other lactic acid bacteria. The phosphoketolase of LMC7 belongs to the xylulose 5-phosphate (X5P)/fructose 6-phosphate (F6P) phosphoketolase (Xfp) family, which is an enzyme with dual specificity for X5P and F6P. The members of this family contain typical thiamin pyrophosphate (TPP) binding sites as reported for other TPP-dependent enzymes, and several highly conserved regions as signature patterns for phosphoketolases. The plasmid pGPK containing the Xfp gene (xfp) exhibits phosphoketolase activity in E. coli. The specific activities of the enzyme from E. coli BL21 and E. coli EC101 harboring xfp were 0.28 and 0.14 units/mg, respectively. They both exhibited a 1.5-fold increase in the production of acetic acid from acetyl phosphate compared with their corresponding original strain.

Complete genome sequence of Staphylococcus equorum KS1039 isolated from Saeu-jeotgal, Korean high-salt-fermented seafood.

Staphylococcus equorum KS1039 was isolated from a form of traditional Korean high-salt-fermented seafood called Saeu-jeotgal, and exhibited growth at a NaCl (w/v) concentration of 25%. Comparative genome analyses with two other strains revealed the presence of two potassium voltage-gated channel genes uniquely in KS1039, which might be involved in salt tolerance. This first complete genome sequence of the species will increase our understanding of the genetic factors allowing it to be safely consumed by humans and to inhabit high-salt environments.

Genetic Diversity and Antibiotic Resistance of Enterococcus faecalis Isolates from Traditional Korean Fermented Soybean Foods

Eighty-five Enterococcus faecalis isolates collected from animals (40 isolates), meju (a Korean fermented soybean product; 27 isolates), humans (10 isolates), and various environmental samples (8 isolates) were subjected to multilocus sequence typing (MLST) to identify genetic differences between samples of different origins. MLST analysis resulted in 44 sequence types (STs), and the eBURST algorithm clustered the STs into 21 clonal complexes (CCs) and 17 singletons. The predominant STs, ST695 (21.1%, 18/85) and ST694 (9.4%, 8/85), were singletons, and only contained isolates originating from meju. None of the STs in the current study belonged to CC2 or CC9, which comprise clinical isolates with high levels of antibiotic resistance. The E. faecalis isolates showed the highest rates of resistance to tetracycline (32.9%), followed by erythromycin (9.4%) and vancomycin (2.4%). All isolates from meju were sensitive to these three antibiotics. Hence, MLST uncovered genetic diversity within E. faecalis, and clustering of the STs using eBURST revealed a correlation between the genotypes and origins of the isolates.

Fiber-Optic Localized Surface Plasmon Resonance sensor combined with micro fluidic channel

This paper proposes Fiber-Optic Localized Surface Plasmon Resonance (FO LSPR) sensor combined with micro fluidic channel, which enables the continuous supply of fluid for bio-reaction. The proposed method can prevent the degradation of the sensing characteristics due to the change of measurement condition. The feasibility of the FO LSPR sensor with micro fluidic channel is proved by Computational Fluid Dynamics simulation (CFD). Also, the proposed method has been evidenced by measuring the output intensity of the FO LSPR sensor at various refractive index solutions. Finally, Prostate Specific Antigen (PSA) immunoassay was measured to verify the possibility of the fabricated sensor system as a biosensor.

Characterization of Mobile Staphylococcus equorum Plasmids Isolated from Fermented Seafood That Confer Lincomycin Resistance.

The complete nucleotide sequences of lincomycin-resistance gene (lnuA)-containing plasmids in Staphylococcus equorum strains isolated from the high-salt-fermented seafood jeotgal were determined. These plasmids, designated pSELNU1–3, are 2638-bp long, have two polymorphic sites, and encode typical elements found in plasmids that replicate via a rolling-circle mechanism including the replication protein gene (rep), a double-stranded origin of replication, a single-stranded origin of replication, and counter-transcribed RNA sequence, as well as lnuA. Plasmid sequences exhibit over 83% identity to other Staphylococcus plasmids that harbor rep and lnuA genes. Further, three pairs of identified direct repeats may be involved in inter-plasmid recombination. One plasmid, pSELNU1, was successfully transferred to other Staphylococcus species, Enterococcus faecalis, and Tetragenococcus halophilus in vitro. Antibiotic susceptibility of the transconjugants was host-dependent, and transconjugants maintained a lincomycin resistance phenotype in the absence of selective pressure over 60 generations.

Bacterial Community Monitoring of Commercial Kimchi Produced in Korea and China with Evidence of Bacilli Spore Formation during Fermentation

Kimchi is the generic term given to a group of fermented vegetable foods in Korea. Kimchi is classified according to major ingredients such as Chinese cabbage, radish, cucumber, and other vegetables. Its fermentation depends on the indigenous microflora on these raw materials. Kimchi has traditionally been made at home, but has begun to be produced industrially as the increased demand by institutional food services follows the rapid growth of industry in the 1970’s. In addition, the demand for commercial kimchi is increasing due to economic growth, changes in family structure, the development of the food processing industry and the increasing number of women working outside the home. At the 1988 Seoul Olympics, kimchi was introduced to many foreign countries and became a global export. Since the registration of kimchi on Codex Alimentarius in 2001, its status has been elevated to a global food, and its market continues to expand worldwide [4]. Currently, Korean imports of price-competitive kimchi are sharply increasing due to the expansion of agricultural imports and the increased demand of the domestic food service industry. According to a survey by the Korea International Trade Association (http://www.kita.net) and the Korea Agro-Fisheries Trade Corp. (http://www.at.or.kr), domestic kimchi demand in 2008 was estimated to be about 1,640,000 tons. Imported kimchi accounted for about 220,000 tons, mostly from China. As imports of the lowpriced Chinese kimchi increase, the kimchi industry in Korea is greatly impacted, affecting production, supply and price of raw materials. Some distributors intentionally mislabel the imported Chinese kimchi as domestically-made kimchi which harms the Korean kimchi industry. According to the report by the Korea Food and Drug Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis was adopted to explore rapid differentiation in the diversity and dynamics of bacteria in kimchi made in Korea and China for future application in kimchi origin discrimination. TRFLP analysis supported the reproducible and rapid detection of major lactic acid bacteria known to be involved in kimchi fermentation. The taxonomic resolution level of this T-RFLP analysis was between the species and genus level, but was not specific enough for the detection of a bacterium found only in one origin, either Korea or China. The bacterial community structure successions in kimchi samples from Korea and China analyzed by T-RFLP analysis occurred with a similar pattern. Bacillus spp. which were not detected in the early microbial studies of kimchi were constantly detected until the late fermentation stage of kimchi in our T-RFLP analysis and their existence was proved by culture-based identification. Additionally, sporulation of Bacillus spp. during kimchi fermentation was discovered.