• 한국생물공학회:학술대회논문집
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• 2001.11a
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• pp.598-601
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• 2001

Citrobacter sp. Y19 was studied for $H_2$ production from glucose in batch culture. Important conditions studied include phosphate concentration, temperature, glucose concentration, and gas-phase replacement. Optimal $H_2$ production was observed at 140 - 180 mM of phosphate and $36^{\circ}C$. When glucose concentration increased from 0.1 to 5% (w/v), $H_2$ production increased up to 2% and remained constant thereafter. Intermittent purging of the reaction bottle with Ar gas stimulated the $H_2$ production by alleviating the inhibition by $H_2$. The maximum productivity was observed to be 113.2 ml $H_2$/h-1.

• Biomedical Science Letters
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• v.16 no.1
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• pp.10-18
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• 2010

The present study was set to develop comprehensive system for assessing the safety of drinking water using PCR-reverse blot hybridization assay (REBA). The REBA developed in this study can detect waterborne pathogens such as Shigella spp., Salmonella spp., Citrobacter spp., Enterobacter spp., Klebsiella spp., Yersinia spp., Mycobacterium spp., Listeria spp. at the genus level, and Escherichia coli, Citrobacter freundii, Klebsiella pneumoniae, Pseudomonas aeruginosa, Yersinia enterocolitica, Y. pseudotuberculosis, Mycobacterium avium complex, M. marinum, Enterococcus faecalis, and Staphylococcus aureus at the species level, and E. coli O157:H7 at the strain level.

• 한국생물공학회:학술대회논문집
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• 2002.04a
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• pp.419-422
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• 2002

Fermentative hydrogen production by Citrobacter sp. Y 19 was investigated in batch culture. Optimal hydrogen production activity was observed at pH 6 - 7 and temperature of $36^{\circ}C$, and hydrogen yield and maximal hydrogen production rate were 1.12 mmol/mmol glucose and 32.3 mmol/g cell${\cdot}$h, respectively. With glucose as a substrate, the bacterium produced ethanol, acetate, and carbon dioxide as major glucose fermentation by-products. Y19 could utilize various sugars such as galactose, fructose, lactose, sucrose, and starch for cell growth and hydrogen production.

• Proceedings of the Korean Society of Life Science Conference
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• 2000.09a
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• pp.58-58
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• 2000

• Toxicological Research
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• v.23 no.1
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• pp.65-72
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• 2007

This study was conducted to obtain information of the oral dose acute toxicity of PGB-2, a novel polyglucosamine polymer produced from Citrobacter sp. BL-4 (a new strain) in male and female mice. Mortality, body weight changes, clinical signs were monitored during 14 days after single oral dose of test article at dose levels of 2000, 1000, 500, 250 and 125 ml/kg. Gross lesions, organ weight and histopathology of principal organs were examined after necropsy. As the results, we could not find any mortalities, clinical signs, changes in the body weight and gross findings except for white foci in the liver. In addition, no PGB-2-treatment related abnormal changes on the organ weight and histopathology of principle organs were detected except for atypical signs of liver. White liver foci were confirmed as focal infiltration of inflammatory cells. The results suggest that the PGB-2 is relatively safe in mice but the possibility of hepatotoxicity could not be excluded. The $LD_{50}$ and approximate LD in mice after single oral dose of PGB-2 were considered over 2000 mg/kg, respectively. In future, the potential hepatotoxicity of PGB-2 should be evaluated through the repeat dose toxicity test prior to develop as a new agent.

• Journal of Microbiology and Biotechnology
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• v.20 no.11
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• pp.1491-1499
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• 2010

Rhizosphere microorganisms possessing phytase activity are considered important for rendering phytate-phosphorus (P) available to plants. In the present study, the Citrobacter braakii phytase gene (appA) was overexpressed in rhizobacteria possessing plant growth promoting (PGP) traits, for increasing their potential as bioinoculants. AppA was cloned under the lac promoter in the broadhost-range expression vector pBBR1MCS-2. Transformation of the recombinant construct pCBappA resulted in high constitutive phytase activity in all of the eight rhizobacterial strains belonging to genera Pantoea, Citrobacter, Enterobacter, Pseudomonas (two strains), Rhizobium (two strains), and Ensifer that were studied. Transgenic rhizobacterial strains were found to display varying levels of phytase activity, ranging from 10-folds to 538-folds higher than the corresponding control strains. The transgenic derivative of Pseudomonas fluorescens CHA0, a well-characterized plant growth promoting rhizobacterium, showed the highest expression of phytase (~8 U/mg) activity in crude extracts. Although all transformants showed high phytase activity, rhizobacteria having the ability to secrete organic acid showed significantly higher release of P from Ca-phytate in buffered minimal media. AppA overexpressing rhizobacteria showed increased P content, and dry weight (shoot) or shoot/ root ratio of mung bean (Vigna radiata) plants, to different extents, when grown in semisolid agar (SSA) medium containing Na-phytate or Ca-phytate as the P sources. This is the first report of the overexpression of phytase in rhizobacterial strains and its exploitation for plant growth enhancement.

• Journal of Microbiology and Biotechnology
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• v.32 no.2
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• pp.176-186
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• 2022

Continued fenvalerate use has caused serious environmental pollution and requires large-scale remediation. Dibutyl phthalate (DBP) was discovered in fenvalerate metabolites degraded by Citrobacter freundii CD-9. Coculturing is an effective method for bioremediation, but few studies have analyzed the degradation pathways and potential mechanisms of cocultures. Here, a DBP-degrading strain (BDBP 071) was isolated from soil contaminated with pyrethroid pesticides (PPs) and identified as Stenotrophomonas acidaminiphila. The optimum conditions for DBP degradation were determined by response surface methodology (RSM) analysis to be 30.9 mg/l DBP concentration, pH 7.5, at a culture temperature of 37.2℃. Under the optimized conditions, approximately 88% of DBP was degraded within 48 h and five metabolites were detected. Coculturing C. freundii CD-9 and S. acidaminiphila BDBP 071 promoted fenvalerate degradation. When CD-9 was cultured for 16 h before adding BDBP 071, the strain inoculation ratio was 5:5 (v/v), fenvalerate concentration was 75.0 mg/l, fenvalerate was degraded to 84.37 ± 1.25%, and DBP level was reduced by 5.21 mg/l. In addition, 12 fenvalerate metabolites were identified and a pathway for fenvalerate degradation by the cocultured strains was proposed. These results provide theoretical data for further exploration of the mechanisms used by this coculture system to degrade fenvalerate and DBP, and also offer a promising method for effective bioremediation of PPs and their related metabolites in polluted environments.

• Journal of Microbiology and Biotechnology
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• v.13 no.5
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• pp.717-724
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• 2003

A newly isolated Citrobacter sp. Y19 catalyzes the CO-dependent $H_2$ production (biological water-gas shift reaction) by the actions of CO dehydrogenase (CODH) and hydrogenase. Y 19 requires $O_2$ for fast growth, but its $H_2$ production activity is significantly inhibited by $O_2$. In the present study, the effect of $O_2$ on the activities of CODH ard hydrogenase was investigated quantitatively in both whole cells and broken cells, based on CO-dependent or methyl viologen (MV)-dependent $H_2$ production in addition to CO-dependent MV reduction. In crude cell extracts, CODH activity was mostly found in the soluble fraction. Inactivation of CODH and hydrogenase activities by $O_2$ followed the first-order decay kinetics, and the dependence of the rate constants on $O_2$ partial pressure could be expressed by the Michaelis-Menten equation. In whole cells, the maximum deactivation rate constants ($k_{d,max}$ of hydrogenase and CODH were quite similar: $0.07{\pm}0.03 min^{-1}\;and\;0.10{\pm}0.04 min^{-1}$, respectively. However, the first-order rate constant ($k_{d,max}/K_s$) of CODH ($0.25\;min^{-1}\;atm^{-1}$) at low $O_2$ partial pressures was about 3-fold higher than that of the hydrogenase, since the half-saturation constant ($K_s$) of CODH was about half of that of hydrogenase. In broken cells, both enzymes became significantly more sensitive to $O_2$ compared to the unbroken cells, while $k_{d,max}/K_s$ increased 37-fold for hydrogenase and 6.7-fold for CODH. When whole cells were incubated under anaerobic conditions after being exposed to air for 1 h, hydrogenase activity was recovered more than 90% in 2 h suggesting that the deactivation of hydrogenase by $O_2$ was reversible. On the contrary, CODH activity was not recovered once deactivated by $O_2$ and the only way to recover the activity was to synthesize new CODH. This study indicates that $O_2$ sensitivity of $H_2$ production activity of Citrobacter sp. Y19 is an important drawback as in other $H_2-producing$ bactria.

• KSBB Journal
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• v.27 no.2
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• pp.75-85
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• 2012

Although, microbial arsenic mobilization by dissimilatory arsenate-reducing bacteria (DARB) and the practical use to the removal technology of arsenic from contaminated soil are expected, most previous research mainly has been focused on the geochemical circulation of arsenic. Therefore, in this review we summarized the previously reported DARB to grasp the characteristic for bioremediation of arsenic. Evidence of microbial growth on arsenate is presented based on isolate analyses, after which a summary of the physiology of the following arsenate-respiring bacteria is provided: Chrysiogenes arsenatis strain BAL-$1^T$, Sulfurospirillum barnesii, Desulfotomaculum strain Ben-RB, Desulfotomaculum auripigmentum strains OREX-4, GFAJ-1, Bacillus sp., Desulfitobacterium hafniense DCB-$2^T$, strain SES-3, Citrobacter sp. (TSA-1 and NC-1), Sulfurospirillum arsenophilum sp. nov., Shewanella sp., Chrysiogenes arsenatis BAL-$1^T$, Deferribacter desulfuricans. Among the DARB, Citrobacter sp. NC-1 is superior to other dissimilatory arsenate-reducing bacteria with respect to arsenate reduction, particularly at high concentrations as high as 60 mM. A gram-negative anaerobic bacterium, Citrobacter sp. NC-1, which was isolated from arsenic contaminated soil, can grow on glucose as an electron donor and arsenate as an electron acceptor. Strain NC-1 rapidly reduced arsenate at 5 mM to arsenite with concomitant cell growth, indicating that arsenate can act as the terminal electron acceptor for anaerobic respiration (dissimilatory arsenate reduction). To characterize the reductase systems in strain NC-1, arsenate and nitrate reduction activities were investigated with washed-cell suspensions and crude cell extracts from cells grown on arsenate or nitrate. These reductase activities were induced individually by the two electron acceptors. Tungstate, which is a typical inhibitory antagonist of molybdenum containing dissimilatory reductases, strongly inhibited the reduction of arsenate and nitrate in anaerobic growth cultures. These results suggest that strain NC-1 catalyzes the reduction of arsenate and nitrate by distinct terminal reductases containing a molybdenum cofactor. This may be advantageous during bioremediation processes where both contaminants are present. Moreover, a brief explanation of arsenic extraction from a model soil artificially contaminated with As (V) using a novel DARB (Citrobacter sp. NC-1) is given in this article. We conclude with a discussion of the importance of microbial arsenate reduction in the environment. The successful application and use of DARB should facilitate the effective bioremediation of arsenic contaminated sites.

• Korean Journal of Medicinal Crop Science
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• v.16 no.2
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• pp.112-117
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• 2008

This experiment was carried out to obtain the basic information on processing for product of high quality goods in Artemisia capillaris. We investigated antioxidant and antimicrobial activities by harvesting date and plant parts in Artemisia capillaris. Contents of total polyphenol compounds and flavonoids were the highest in leaf, followed by capitulum and stem. Leaf on June 30 contained 76.7 mg/g DW total phenolic compounds and 78.2 mg/g DW flavonoids. As $RC_{50}$ value, that was, the concentration of sample required for 50% reduction of DPPH (2,2-diphenyl-l-picrylhydrazyl) absorbance, was very low as $5.42\;{\mu}g$ in leaf on June 30, antioxidant activity was the highest. In addition, $RC_{50}$ of BHA, BHT and ${\alpha}-tocopherol$ were $3.09\;{\mu}g$, $24.30{\mu}g$ and $2.87{\mu}g$, respectively. And capitulum had antimicrobial activities against Bacillus subtilis, Staphylococcus aureus, Enterobacter aerogenes, Citrobacter freundii, Vibrio vulnificus, Pseudomonas aeruginosa, Saccharomyces cerevisiae. By the way, leaf and stem rarely had antimicrobial activity. Antimicrobial activities of capitulum according to harvesting date were very various. Capitulum on August 30 had the highest antimicrobial activities against Bacillus subtilis, Staphylococcus aureus, Vibrio vulnificus, Saccharomyces cerevisiae and on July 30 against Enterobacter aerogenes, Citrobacter freundii, Pseudomonas aeruginosa.