• Toxicological Research
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• v.28 no.1
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• pp.19-24
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• 2012

In the present study, toxicity of silver nanoparticles (AgNPs) was investigated in the nematode, Caenohabditis elegans focusing on the upstream signaling pathway responsible for regulating oxidative stress, such as mitogen-activated protein kinase (MAPK) cascades. Formation of reactive oxygen species (ROS) was observed in AgNPs exposed C.elegans, suggesting oxidative stress as an important mechanism in the toxicity of AgNPs towards C. elegans. Expression of genes in MAPK signaling pathways increased by AgNPs exposure in less than 2-fold compared to the control in wildtype C.elegans, however, those were increased dramatically in sod-3 (gk235) mutant after 48 h exposure of AgNPs (i.e. 4-fold for jnk-1 and mpk-2; 6-fold for nsy-1, sek-1, and pmk-1, and 10-fold for jkk-1). These results on the expression of oxidative stress response genes suggest that sod-3 gene expression appears to be dependent on p38 MAPK activation. The high expressions of the pmk-1 gene 48 h exposure to AgNPs in the sod-3 (gk235) mutant can also be interpreted as compensatory mechanisms in the absence of important stress response genes. Overall results suggest that MAPK-based integrated stress signaling network seems to be involved in defense to AgNPs exposure in C.elegans.

• Journal of Microbiology and Biotechnology
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• v.13 no.6
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• pp.976-983
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• 2003

Seven Escherichia coli cells defective with aerobic growth were isolated by the insertion of ${\lambda}placMu53$, a hybrid bacteriophage of ${\lambda}$ and Mu, which created a transcriptional fusion to lacZY. These insertion mutant cells were tested on an XG ($5-bromo-4-chloro-3-indolyl-{\beta}-D-galactopyranoside$) medium for anaerobic expression of lacZ by fusion to a promoter. The chromosomal DNA from these strains were digested by EcoRI, and the EcoRI fragments that contained the fused gene and lacZ sequence were identified by Southern hybridization, using lacZ containing plasmid as a probe. The EcoRI fragment from each strain was cloned and sequenced. The sequence data were compared with the GenBank database. The mutated gene of three strains, CYT4, CYT5, and OS11, was found to be identical, and it was nrdAB that encoded ribonucleoside diphosphate reductase. The gene nrdAB was at min 50.5 on the Escherichia coli linkage map and 2,348,084 on the physical map, and is involved in hemAe-related reduction-oxidation reaction. OS6 and OS14 mutant strains had insertion at min 8.3 and the mutated gene was hemB. The hemB encodes 5-aminolevulinate dehydratase or porphobilinogen synthase. The OS3 mutant had insertion in cydB at min 16.6. The cydAB encodes cytochrome d oxidase. In the case of OS1, the fusion was made with sucA, the E1 component of ${\alpha}-ketoglutarate$ dehydrogenase.

• Bulletin of the Korean Chemical Society
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• v.22 no.5
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• pp.514-518
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• 2001

We have explored the importance of two ATP binding domains of Hsp104 protein in protection of yeast cells from cadmium exposure. In the previous study we have discovered that the presence of two ATP binding sites was essential in providing heat sh ock protection as well as rescuing cells from oxidative stress. In this paper we first report wild type cell with functional hsp104 gene is more resistant to cadmium stress than hsp104-deleted mutant cell, judging from decrease in survival rates as a result of cadmium exposure. In order to demonstrate functional role of two ATP binding sites in cadmium defense, we have transformed both wild type (SP1) and hyperactivated ras mutant (IR2.5) strains with several plasmids differing in the presence of ATP binding sites. When an extra copy of functional hsp104 gene with both ATP binding sites was overexpressed with GPD-promoter, cells showed increased survival rate against cadmium stress than mutants with ATP binding sites changed. The degree of protection in the presence of two ATP binding sites was similarly observed in ira2-deleted hyperactivated ras mutant, which was more sensitive to oxidative stress than wild type cell. We have concluded that the greater sensitivity to cadmium stress in the absence of two ATP binding sites is attributed to the higher concentration of reactive oxygen species (ROS) produced by cadmium exposure based on the fluorescence tests. These findings, taken all together, imply that the mechanism by which cadmium put forth toxic effects may be closely associated with the oxidative stress, which is regulated independently of the Ras-cAMP pathway. Our study provides a better understanding of cadmium defense itself and cross-talks between oxidative stress and metal stress, which can be applied to control human diseases due to similar toxic environments.

• Microbiology and Biotechnology Letters
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• v.31 no.4
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• pp.395-399
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• 2003

Nebramycin is a complex of aminocyclitol compounds that is produced by aerobic culture in fermentation process. The major antibiotic factors produced by Streptoalloteichus hindustanus are nebramycin factor 2, 4, 5'and kanamycin A. A mutant was selected, producing nebramycin factor 5' activity 16.4 times higher than parent strain by microbiological assay using Pseudomonas aeruginosa CH-U34AF. The component ratio of nebramycin factor 5' was dramatically increased from 34% to 70% by the optimization of fermentation condition. It was found that the component ratio of nebramycin factor 5' in fermentation was especially affected by the oxygen transfer rate. Optimum oxygen transfer rate for maximal nebramycin factor 5' productivity and ratio during S. hindustanus fermentation was elucidated to $0.50 mMO_2$/min.

• BMB Reports
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• v.31 no.6
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• pp.595-599
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• 1998

To investigate conformational information of a low oxygen affinity recombinant hemoglobin (rHb) containing $96Val{\rightarrow}Trp$ mutation at the ${\alpha}96$ position, we ave produced rHb (${\alpha}96Val{\rightarrow}Phe$) and rHb (${\alpha}96Val{\rightarrow}Tyr$), using the Escherichia coli expression system and site-directed mutagenesis. The oxygen affinity of rHb (${\alpha}96Val{\rightarrow}Phe$) is similar to that of human normal adult hemoglobin (Hb A). However, the oxygen affinity of rHb (${\alpha}96Val{\rightarrow}Tyr$) showed much lower oxygen affinity than Hb A which is similar to that of rHb (${\alpha}96Val{\rightarrow}Tyr$), providing an opportunity as a potential candidate for a hemoglobin-based blood substitute. Both rHb (${\alpha}96Val{\rightarrow}Phe$) and rHb (${\alpha}96Val{\rightarrow}Tyr)$ showed high cooperativity in oxygen binding. IH-NMR spectroscopy shows that both rHb (${\alpha}96Val{\rightarrow}Phe$) and rHb (${\alpha}96Val{\rightarrow}Tyr$) have very similar tertiary structure around the heme pockets and uaternary structure in the ${\alpha}_1/{\beta}_2$ subunit interface ompared to Hb A. The low oxygen affinity of rHb (${\alpha}96Val{\rightarrow}Tyr$) has been suggested to be due to a hydrogen bond caused by an extra hydroxyl group not present in rHb (${\alpha}96Val{\rightarrow}Phe$). However, investigation of the carbonmonoxy form of rHb (${\alpha}96Val{\rightarrow}Phe$) and (${\alpha}96Val{\rightarrow}Try$) in the presence of inositol hexaphosphate at low temperature suggests that low oxygen affinity of (${\alpha}96Val{\rightarrow}Try$) may arise from a mechanism different to that of rHb (${\alpha}96Val{\rightarrow}Trp$).

• 한국균학회소식:학술대회논문집
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• 2015.05a
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• pp.13-13
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• 2015

Rice blast fungus, Magnaporthe oryzae, is the most destructive pathogen of rice in the world. This fungus has a biotrophic phase early in infection and switches to a necrotrophic lifestyle after host cell death. During the biotrophic phase, the fungus competes with host for nutrients and oxygen. Continuous uptake of oxygen is essential for successful establishment of blast disease of this pathogen. Here, we report transcriptional responses of the fungus to oxygen limitation. Transcriptome analysis using RNA-Seq identified 1,047 up-regulated genes in response to hypoxia. Those genes were involved in mycelial development, sterol biosynthesis, and metal ion transport based on hierarchical GO terms and well-conserved among three different fungal species. In addition, null mutants of three hypoxia-responsive genes were generated and tested for their roles on fungal development and pathogenicity. The mutants for a sterol regulatory element-binding protein gene, MoSRE1, and C4 methyl sterol oxidase gene, ERG25, exhibited increased sensitivity to hypoxia-mimetic agent, increased conidiation, and delayed invasive growth within host cells, suggesting important roles in fungal development. However, such defects did not cause any significant decrease in disease severity. The other null mutant for alcohol dehydrogenase gene, MoADH1, showed no defect in the hypoxia-mimic condition and fungal development. Taken together, this comprehensive transcriptional profiling in response to a hypoxia condition with experimental validations would provide new insights on fungal development and pathogenicity in plant pathogenic fungi.

• Microbiology and Biotechnology Letters
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• v.19 no.1
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• pp.76-81
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• 1991

- The effect of redox potential (ORP) on lysine production by a leucine auxotrophic regulatory mutant of Corynebacterium glutclmicum on molasses medium was investigated in a 2-1 jar fermentor at pH 6.9 and $32^{\circ}C$. At a dilution rate of D=O.l $h ^1$, a maximum yield of Yr,,s=0.24 was obtained in either carbon- or leucine-limited chemostat where the redox potential was between -60 mV and - 100 mV. This level of redox potential corresponded to moderate oxygen deficiency. Under a high oxygen deficient condition of the redox potential of - 130 rnV (oxygen-limited chemostat), all the kinetic parameters such as $Y_[p/s}, q_s\; and \; q_p$ were decreased significantly and significant amounts of byproducts including glycine, alanine and valine were accumulated in the culture, indicating that the control of redox potential is important in lysine fermentation. At the redox potential of - 40 mV, on the other hand, large quantities of arginine (up to 0.38g/l) and glutamic acid (up to 0.12 g/l) were produced. A maximum lysine productivity of 2.41 g/l/h was achieved at - 66 mV under a carbon-limited condition.

• Korean Chemical Engineering Research
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• v.47 no.4
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• pp.506-511
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• 2009

In order to improve the bacterial cellulose(BC) production yield, centrifugal and inclined centrifugal impellers were developed. A 6 flat-blade turbine impeller was used as a control system. The flow pattern in the fermenter and volumetric oxygen transfer coefficient($k_La$) of these fermentation systems were studied. Fermentations were carried out for the production of BC by G. hansenii PJK in a 2-L jar fermenter equipped with new impellers. Liquid medium was circulated from the bottom, through the cylinder of the impeller and to the wall. The volumetric oxygen transfer coefficients, $k_La$, of inclined centrifugal and centrifugal impeller systems at 100 rpm were 23 and 15% of the conventional turbine impeller system, respectively. However, the conversion of microbial cells to cellulose non-producing mutant decreased and this results in the increase in BC production at low rotating speed of impellers.

• Journal of Microbiology
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• v.44 no.3
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• pp.284-292
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• 2006

The cbb3 cytochrome c oxidase has the dual function as a terminal oxidase and oxygen sensor in the photosynthetic bacterium, Rhodobacter sphaeroides. The cbb3 oxidase forms a signal transduction pathway together with the PrrBA two-component system that controls photosynthesis gene expression in response to changes in oxygen tension in the environment. Under aerobic conditions the cbb3 oxidase generates an inhibitory signal, which shifts the equilibrium of PrrB kinase/phosphatase activities towards the phosphatase mode. Photosynthesis genes are thereby turned off under aerobic conditions. The catalytic subunit (CcoN) of the R. sphaeroides cbb3 oxidase contains five histidine residues (H2l4, B233, H303, H320, and H444) that are conserved in all CcoN subunits of the cbb3 oxidase, but not in the catalytic subunits of other members of copper-heme superfamily oxidases. H214A mutation of CcoN affected neither catalytic activity nor sensory (signaling) function of the cbb3 oxidase, whereas H320A mutation led to almost complete loss of both catalytic activity and sensory function of the cbb3 oxidase. H233V and H444A mutations brought about the partial loss of catalytic activity and sensory function of the cbb3 oxidase. Interestingly, the H303A mutant form of the cbb3 oxidase retains the catalytic function as a cytochrome c oxidase as compared to the wild-type oxidase, while it is defective in signaling function as an oxygen sensor. H303 appears to be implicated in either signal sensing or generation of the inhibitory signal to the PrrBA two-component system.

• Journal of Ginseng Research
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• v.43 no.2
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• pp.218-225
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• 2019

Background: Streptococcus pneumoniae, more than 90 serotypes of which exist, is recognized as an etiologic agent of pneumonia, meningitis, and sepsis associated with significant morbidity and mortality worldwide. Immunization with a pneumococcal pep27 mutant (${{\Delta}}pep27$) has been shown to confer comprehensive, long-term protection against even nontypeable strains. However, ${{\Delta}}pep27$ is effective as a vaccine only after at least three rounds of immunization. Therefore, treatments capable of enhancing the efficiency of ${{\Delta}}pep27$ immunization should be identified without delay. Panax ginseng Mayer has already been shown to have pharmacological and antioxidant effects. Here, the ability of Korean Red Ginseng (KRG) to enhance the efficacy of ${{\Delta}}pep27$ immunization was investigated. Methods: Mice were treated with KRG and immunized with ${{\Delta}}pep27$ before infection with the pathogenic S. pneumoniae strain D39. Total reactive oxygen species production was measured using lung homogenates, and inducible nitric oxide (NO) synthase and antiapoptotic protein expression was determined by immunoblotting. The phagocytic activity of peritoneal macrophages was also tested after KRG treatment. Results: Compared with the other treatments, KRG significantly increased survival rate after lethal challenge and resulted in faster bacterial clearance via increased phagocytosis. Moreover, KRG enhanced ${{\Delta}}pep27$ vaccine efficacy by inhibiting reactive oxygen species production, reducing extracellular signal-regulated kinase apoptosis signaling and inflammation. Conclusion: Taken together, our results suggest that KRG reduces the time required for immunization with the ${{\Delta}}pep27$ vaccine by enhancing its efficacy.