• Korean Journal of Microbiology
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• v.52 no.1
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• pp.49-58
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• 2016

Compared to planktonic bacterial populations, biofilms have distinct bacterial community structures and play important ecological roles in various aquatic environments. Despite their ecological importance in nature, bacterial community structure and its succession during biofilm development in the Antarctic marine environment have not been elucidated. In this study, the succession of bacterial community, particularly during the early stage of biofilm development, in the Antarctic marine environment was investigated by pyrosequencing of the 16S rRNA gene. Overall bacterial distribution in biofilms differed considerably from surrounding seawater. Relative abundance of Gammaproteobacteria and Bacteroidetes which accounted for 78.9-88.3% of bacterial community changed drastically during biofilm succession. Gammaproteobacteria became more abundant with proceeding succession (75.7% on day 4) and decreased to 46.1% on day 7. The relative abundance of Bacteroidetes showed opposite trend to Gammaproteobacteria, decreasing from the early days to the intermediate days and becoming more abundant in the later days. There were striking differences in the composition of major OTUs (${\geq}1%$) among samples during the early stages of biofilm formation. Gammaproteobacterial species increased until day 4, while members of Bacteroidetes, the most dominant group on day 1, decreased until day 4 and then increased again. Interestingly, Pseudoalteromonas prydzensis was predominant, accounting for up to 67.4% of the biofilm bacterial community and indicating its important roles in the biofilm development.

• Journal of Life Science
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• v.29 no.9
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• pp.986-995
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• 2019

Intestinal microbiota play a key role in maintaining the host's health, and variety and richness of this microbiota is directly influenced and modulated by the host's diet. Kimchi is a fermented food rich in dietary fibers and lactic acid bacteria (LAB). To investigate the effect of fermented kimchi on the host's response and the composition of intestinal microbiota, 45 male Sprague-Dawley rats six weeks old were divided into three experimental groups that received either a basal diet (CON) or a basal diet supplemented with fermented kimchi (FK) or chitosan-added fermented kimchi (CFK) for four weeks. Body weights and feed intakes were measured weekly, and the intestinal contents were collected aseptically and were used for 16S rRNA gene profiling via pyrosequencing. As compared to the control, FK and CFK groups showed less body weight gain, feed efficiency, and blood triglyceride concentration. The diversity of intestinal microbiota was increased in both FK and CFK as compared to the control. At the phylum level, obesity-associated Firmicutes decreased, while leanness-associated Bacteroidetes increased. At the genus-level, the genera that consist of LAB, leanness-associated bacteria, and butyric acid-producing bacteria increased in FK and CFK as compared to the control. The overall results suggest that the consumption of fermented kimchi can reduce obesity and promote the host's health through mechanisms involving the modulation of intestinal microbiota.

• Korean Journal of Microbiology
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• v.51 no.4
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• pp.448-452
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• 2015

The bacterial strain that was isolated from chinese cabbage rhizosphere, showed inhibition of yeast growth. This strain was identified as Pseudomonas fluorescens BB2 by API 20NE test and 16S rRNA gene sequence analysis. P. fluorescens BB2 strain produced antibiotics against yeast as a secondary metabolite effectively when the culture was carried out in YM medium with 3% glucose at $20^{\circ}C$. The protein antibiotic of BB2 strain which was concentrated by ammonium sulfate precipitation and n-butanol extraction inhibited the growth of yeast with the minimal inhibitory concentration of $10{\mu}g/ml$ against Candida albicans KCTC 7965, and the growth of yeast was completely inhibited at $80{\mu}g/ml$. The hydrophilic fraction of n-butanol extraction inhibited the growth of Bacillus cereus ATCC 21366, showed orange halo on chrome azurol S plate, which means the fraction contained iron chelating siderophore. The results of crystal violet uptake through the cell membrane showed that membrane permeability was increased about 9% than control, when the concentration of hydrophobic antibiotic against yeast C. albicans was $60{\mu}g/ml$. As a result, the antibiotic produced by P. fluorescens BB2 against yeast Candida is considered antimicrobial peptide, and this is the first report in the genus Pseudomonas.

• Journal of Life Science
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• v.23 no.2
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• pp.259-266
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• 2013

To isolate the fibrinolytic enzyme, 268 strains from 21 samples were morphologically isolated from Cheonggukjang collected from Korea and Japan. Among the 268 strains, protease-producing bacteria were isolated in nutrient agar medium including 1% skimmed milk. As a result of this, 22 strains were isolated. Apiweb site was used to identify these strains based on their biochemical properties. In addition, 16S rRNA sequencing was performed to identify the strain. Most of the identified strains were Bacillus subtilis and B. amyloliquefaciens. Fibrinolytic enzyme activity was measured with the fibrin plate method. Five strains were finally selected: A2-14, A2-20, C1-05, C1-09, and F2-01. Of those five strains, the A2-20 strain, which is close to B. amyloliquefaciens, showed the strongest fibrinolytic activity. The fibrinolytic enzyme produced by the A2-20 strain was partially purified from culture supernatant by gel filtration and ion exchange chromatography. The optimal pH and temperature values of the partially purified enzyme were 7.0 and $35^{\circ}C$, respectively. Purified protein analysis was carried out with SDS-PAGE and zymography. A genetic analysis was also conducted by PCR based on the consensus sequence of fibrinolytic enzyme. Corresponding genes with a partial sequence of the A2-20 strain were identified.

• Journal of Life Science
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• v.33 no.6
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• pp.481-489
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• 2023

The taste and quality of soy sauce, a fermented liquid condiment, is greatly influenced by microbial metabolism during fermentation. To investigate the microbiological characteristics of ganjang during the initial fermentation process, we prepared meju (fermented soybean) blocks fermented with starter cultures and solar salts and analyzed the microbial community quantitively using 16S rRNA gene profiling from ganjang that had been fermented over a five-week period. The ganjang samples were collected and analyzed after soaking for week one (1W), three (3W), and five (5W) weeks. We found that Halomonadaceae was significantly higher in the 1W group (89.83%) than the 3W and 5W groups (14.46%, and 13.78%, respectively). At a species level, Chromohalobacter beijerinckii and Chromohalobacter canadensis were the dominant species in the 1W group but several taxa such as Bacillus subtilis, Pediococcus acidilactici, and Enterococcus faecalis were more abundant in the 3W and 5W groups. Pearson correlation analysis of the relative abundance of the bacteria showed a negative correlation between Chromohalobacter and two bacterial genera Bacillus and Enterococcus. Beta-diversity showed a statistical distinction between the 1W and the 3W and 5W groups, while no significance was evident between the 3W and 5W groups. Linear discriminant effect size analysis was used to identify biomarkers and significant differences in the relative abundance of several halophilic bacteria, Bacillus sp. and lactic acid bacteria at 1W, 3W, and 5W, recpectively, which indicates the important role of the bacterial community at these time points.

• Journal of Veterinary Clinics
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• v.31 no.3
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• pp.194-198
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• 2014

Methicillin-resistant staphylococci (MRS) are emerging as important pathogens in humans and animals worldwide. The aim of this study was to investigate the prevalence of MRS in the racehorse population and in horse-related personnel in Korea. A total of 195 horses and 18 humans (eight veterinarians, three veterinary hospital staff, and seven horse-handlers) from racehorse farms in Korea were included in the study. The samples were collected from nasal cavities using bacterial transport medium and were cultivated on tryptic soy agar with 5% sheep blood for 3 days at $37^{\circ}C$ to confirm the presence of Staphylococcus spp. Presumptive Staphylococcus spp. isolates were identified by 16S ribosomal RNA gene analysis. The coagulase test and oxacillin susceptibility tests were performed using the tube dilution and disk diffusion methods, respectively. The presence of the mecA gene was determined using a polymerase chain reaction assay. Of the 195 horses, 29 (15.6%) yielded 29 MRS isolates. Twelve (66.7%) of the 18 horse-related personnel yielded 12 MRS isolates. All of the MRS isolates from horses or horse-related personnel were identified as methicillin-resistant coagulase-negative staphylococci (MRCNS). The result of this study suggest that the prevalence of MRS increased with the duration of antibiotic use (p = 0.002). This study also provides evidence for the zoonotic transmission of MRCNS between horses and humans, although further investigations are needed.

• Journal of Life Science
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• v.25 no.6
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• pp.680-685
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• 2015

Previously, cellulase and xylanase producing microorganism, Bacillus subtilis NC1, was isolated from soil. Based on the 16S rRNA gene sequence and API 50 CHL test the strain was identified as Bacillus subtilis, and named as B. subtilis NC1. We cloned and sequenced the genes for cellulase and xylanase. Plus, the deduced amino acid sequences from the genes of cellulase and xylanase were determined and were also identified as glycosyl hydrolases family (GH) 5 and 30, respectively. In this study to optimize the medium parameters for cellulase production by B. subtilis NC1 the RSM (response surface methodology) based on CCD (central composite design) model was performed. Three factors, tryptone, yeast extract, and NaCl, for N or C source were investigated. The cellulase activity was measured with a carboxylmethyl cellulose (CMC) plate and the 3,5-dinitrosalicylic acid (DNS) methods. The coefficient of determination (R²) for the model was 0.960, and the probability value (p=0.0001) of the regression model was highly significant. Based on the RSM, the optimum conditions for cellulase production by B. subtilis NC1 were predicted to be tryptone of 2.5%, yeast extract of 0.5%, and NaCl of 1.0%. Through the model verification, cellulase activity of Bacillus subtilis NC1 increased from 0.5 to 0.62 U/ml (24%) compared to the original medium.

• Journal of Life Science
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• v.22 no.6
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• pp.823-827
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• 2012

A bacterial strain producing a fibrinolytic enzyme, subtilisin CP-1, was isolated from Doen-Jang, a Korean traditional fermentation food. Based on the analysis of gene sequence of 16S rRNA and biochemical analysis, the strain was identified as Bacillus sp. and named as Bacillus sp. CP-1. To investigate the effect of the medium on the production of fibrinolytic enzyme from Bacillus sp. CP-1, two commercial bacterial culture media, tryptic soy broth (TSB) and Luria-Bertani (LB), were applied to the cultivation of Bacillus sp. CP-1. The strain secreted only one proteolytic enzyme (subtilisin CP-1) in the culture broth. The molecular weight of subtilisin CP-1 was estimated to be 28 kDa. Subtilisin CP-1 was optimally active at pH 9.0 and $45^{\circ}C$, and exhibited high specificity for Meo-Suc-Arg-Pro-Tyr-pNA (S-2586), a synthetic chromogenic substrate for chymotrypsin. The first eight amino acid residues of the N-terminal sequence of the enzyme are AQSVPYGI; this sequence is identical to that of subtilisin NAT and E.

• Korean Journal of Microbiology
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• v.47 no.3
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• pp.275-280
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• 2011

In order to evaluate the diversity and change of bacterial population during the manufacturing process of traditional soybean paste (doenjang), bacterial communities were analyzed using 16S rRNA gene-based pyrosequencing. In rice straw, the most important inoculum source for fermentation, the bacterial sequences with a relative abundance greater than 1% were assigned to four phyla, Proteobacteria (71%), Actinobacteria (20.6%), Bacteroidetes (4.2%), and Firmicutes (1.3%). Unlike bacterial community composition of rice straw, a different pattern of bacterial population in meju was observed with predominantly high abundance (99.1%) of Firmicutes. Phylum composition in young doenjang was almost same as that of meju. Major genera in young doenjang were Bacillus (81.3%), Clostridium (6.9%) and Enterococcus (6.3%) and the predominant species among bacterial population was B. amyloliquefaciens (63.6%). Abundance of the phylum Firmicutes in mature doenjang was 99.98%, which was even higher value than those in meju and young doenjang. Predominant species in mature doenjang were B. amyloliquefaciens (67.3%), B. atrophaeus (12.7%), B. methylotrophicus (6.5%), B. mojavensis (3.2%), and B. subtilis. (2.5%), which were also identified as major species of the microbial flora in meju. These results suggested that rice straw was a primary source for supplement of Bacillus species in manufacturing the traditional doenjang and that some species of Bacillus strains were mainly involved in the fermentation process of traditional doenjang.

• Korean Journal of Microbiology
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• v.50 no.4
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• pp.319-326
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• 2014

Two bacterial strains, named as LE17 and LE22, were isolated from traditionally fermented soybean products in order to select lactic acid bacteria for the reduction of biogenic amines and harmful bacteria. Both strains were identified as Pediococcus pentosaceus by 16S rRNA sequence analysis and additional biochemical tests. The strain LE17 reduced the amines by 13.7% for histamine and by 25.9% for tyramine, when it grew in minimal synthetic media containing 0.1% (w/v) histamine and 0.1% tyramine at $30^{\circ}C$ for 48 h, while the strain LE22 reduced the amines by 23.7% for histamine and by 15.7% for tyramine. Both strains also had broad inhibition spectra against pathogens. Considering their properties, they could be used as starters for industrial soybean fermentation.