• The Korean Journal of Food And Nutrition
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• v.9 no.1
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• pp.21-28
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• 1996

This study was attempted to investigate the production of L-tyrosine by Brevibacterium flavum ATCC 14067. To select the strain which produce more L-tyrosine, mutants were induced by N-methyl-N'-nitro-nitrosoguanidine (NTG) treatment and phenylalanine auxotrophic mutants were induced by NTG and penicillin treatments. PFP resistant mutant was isolated from a phenylalanine auxotroph by retreatment with NTG and screened for increase of L-tyrosine production. PFP-326 mutant resistant to PPP (100ug/ml) was derived from phenylalanine auxotroph by mutagenesis with NTG and PFP-106 mutant resistant to PFP (1201g/ml) was derived from PFP-326 by mutagenesis with NTG. The composition of media for L-tyrosine production in strain PFP-106 was studied. PFP-106 mutant strain produced 50mg 11 of L-tyrosine while the parent strain produced 0.56mg 11 of L-tyrosine. The optimum composition of medium for L-tyrosine by strain PFP-106 was 10cA sucrose as carbon source, 3% ammonium sulfate as nitrogen source. The optimum cultural condition for producing L-tyrosine by strain PFP-106 was L-phenylalanine at a concentration of 1000g/mg.

• YAKHAK HOEJI
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• v.58 no.1
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• pp.7-11
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• 2014

To study the resistance mechanism of E. faecalis to LCB01-0371, several resistant mutants to LCB01-0371 or linezolid were isolated by step-wise selection. The frequency of spontaneous mutations resistant to LCB01-0371 was lower than that of linezolid in E. faecalis. The genetic variations in resistant mutants were analyzed by DNA sequencing of domain V of 23S rRNA in each mutant. The first-step mutant to LCB01-0371 had a G2576T point mutation in V domain of 23S rRNA. However, no resistant mutant to LCB01-0371 was isolated in second-step mutant selection.

• Journal of Microbiology and Biotechnology
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• v.3 no.2
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• pp.78-85
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• 1993

In order to elucidate the mechanism which regulates the production of cyclodextrin glucanotransferase (CGTase) and to achieve overproduction of CGTase by releasing catabolite (glucose) repression, several catabolite repression resistant mutants were selected from newly screened Bacillus firmus var. alkalophilus H609, after NTG (N-methyl-N -nitro-N-nitrosoguanidine) treatment, using 2-deoxyglucose as a nonmetabolizable analog of catabolite glucose and as a selection marker. Five catabolite repression resistant mutants were selected from about 30, 000 2-deoxyglucose resistant colonies. Relative catabolite repression indices of the selected mutants were in the range of 8~80% assuming 100% for parent strain. The amount of CGTase produced by the mutant strain CR41, which was 250 units/ml, was three times larger than that produced by its parent strain. The mutation seems to have occurred in the regulatory region of CGTase gene and not in the structural region or the glucose transporting system in cell membrane. The enzymatic properties of CGTase excreted from parent and mutant strains were also compared.

• Journal of Microbiology and Biotechnology
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• v.14 no.4
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• pp.653-657
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• 2004

The cold resistant mutants of P. fluorescens strain $PRS_{9}$ and ATCC13525 were developed which could grow equally well at $28^{\circ}C$ and $10^{\circ}C$. All the mutants were tested for siderophore production, of which $CRPF_9$ (ATCC13525 mutant) was selected, as there was a 16.8-fold increase when compared to its wild-type. Under in vitro conditions, $CRPF_9$ showed better growth promotion both in wheat (29.1% increase in root length) and mung bean (51.5% increase in root length) at $10^{\circ}C$. Greenhouse trials showed a significant increase in root (13.84cm) and shoot (15.0cm) length of $CRPF_9$-treated mung bean seeds, indicating increased rhizocompetence of the mutant. Ferric citrate was a better iron source than ferric hydroxide for plant growth.

• Journal of Microbiology and Biotechnology
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• v.9 no.5
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• pp.613-618
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• 1999

L-Proline-producing mutant strains were developed by exposing L-glutamic acid-producing bacteria to N-metyl-N-nitro-nitrosoguanidine and UV irradiation. A L-histidine auxotroph of Corynebacterium acetoacidophilum RYU3161(KCTC 0616BP), which was resistant to sulfaguanidine and proline analogs (DHP, AZC, TAC), was isolated. The activity of the mutant strain's $\gamma$-glutamyl kinase was 45% higher than that of the parent strain. The optimum level of L-histidine for production of L-proline was 0.16 g/l. In a 5-1 jar fermenter, the mutant strain produced L-proline at a high concentration (35 g/l) level within 48 h of cultivation.

• Microbiology and Biotechnology Letters
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• v.21 no.6
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• pp.549-555
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• 1993

The production of cellulase by Pseudomonas sp. LBC505 isolated was under the strict genetic and biochemical control mechanisms such as catabolit repression and induction. These biochemical control reduced cellulase production. Thus LBC505 was mutated to increase enzyme yields. Cells growth and cellulase production were inhibited by the addition of 2-deoxy glucose (2-DG), which is presumed to function as repressor for the selection of high cellulase yielding mutant.

• Journal of the Korean Society of Tobacco Science
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• v.20 no.1
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• pp.57-65
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• 1998

This study was conducted to develop a resistant tobarro against Potato virus Y (PVY) by transformation of the plants with genetically engineered viral genes. The complimentary DNAs (cDNAS) of potato virus Y-necrosis strain (PVY-Vn) replicase mutant genes (3'-deleted, 5'-deleted and ADD-mutant Nlbs) were synthesized through RT-PCR by using purified PVY-VN RNA and synthesized primers, and cloned in the sense orientation into a plant expression vector (pMBPI), The cDNAS of the genes were transferred into Agrobacterium tumefaciens LBA 4404, and then transformed into tobacco (Nicotiana tabacum cv. Burley 21) plants. Regenerated plants were tested for PVY resistance by inoculation test; 13 transgenic plants including 7 for 3'-deleted Nlb, 3 for 5'-deleted Nlb, and 3 for ADD-mutant Nlb appeared to be resistant at 4 weeks after inoculation with PVY-VN. Among the 13 transgenic tobacco plants, 8 plants had no symptom up to 14 weeks after inoculation. The progenies ($T_1$) from self-fertilization of the transgenic lines varied 0.0% to 81.2% in their resistance (% of resistant plants). The analysis of Nlb-31deleted, -5'deleted and -ADD mutant in the $T_1$ plants by polymerase chain reaction (PCR) showed that Nlb-3'deleted, -5'deleted and -ADD mutants were detected in all of the resistant plants. These results suggest that the PVY resistance was inherited in the $T_1$ generation.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.43 no.6
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• pp.637-641
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• 2010

The antibiotics-resistance profiles of 28 strains of Vibrio parahaemolyticus isolated from seawater were investigated. All of the strains studied were resistant to ampicillin (100%), but susceptible to 12 other antibiotics. The minimum inhibitory concentration (MIC) of V. parahaemolyticus to ampicillin was as high as $1,024-2,048\;{\mu}g{\cdot}mL^{-1}$. The phenotype of strain 8 changed from ampicillin-resistant to susceptible with an in-frame deletion mutant of VPA0477, a putative ${\beta}$-lactamase gene, and the MIC for ampicillin of the mutant strain was $1{\mu}g{\cdot}mL^{-1}$. In conclusion, our findings suggest that the VPA0477 gene acts as a ${\beta}$-lactamase in ampicillin-resistant V. parahaemolyticus strains.

• Korean Journal of Microbiology
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• v.25 no.4
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• pp.290-296
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• 1987

Some streptomycin resistant strains of Rhizobium trifolii having nodulation ability were selected, and their nitrogenase activities, symbiotic effects on plant growth, and nodule electronmicroscope were compared with those of the wild type. After NTG treatment, as a mutagen, at the concentration exhibiting 99.7% lethal rate, 5 strains of streptomycin resistant mutant having nodulating ability were selected. Among these nodulating mutant strains, 3 strains produced more nodules and 2 strains showed less nodules than wild type. But their nitrogenase activities were decreased significantly, and nodule formation time was also delay compared with those of the wild type, and there was no remarkable difference in effects on plant growth. Microstructure of nodules by electronmicroscopy had mant distinctive differences between red clover nodules inoculated with wild type and mutants.

• Journal of Microbiology and Biotechnology
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• v.3 no.2
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• pp.95-98
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• 1993

This study was carried out to isolate and characterize the mutant strains of Schwanniomyces castellii NRRL Y-2477. Mutants were prepared with the treatment of ethyl methane sulfonate. 2-deoxy-D-glucose resistant mutants were isolated and two mutants were selected based on their high production of amylolytic enzymes and their ability to ferment starch. The mutants selected had higher a-amylase and glucoamylase activities than the wild type strain from several other carbon sources. Especially, it was revealed that mutant strain M-9, when cultured in the presence of glucose as a sole carbon source, shows relatively high activities of a-amylase and glucoamylase compared to those of the wild type strain. In result, this mutant strain can be considered as a constitutive producer of amylolytic enzymes. To compare the ethanol production ability of wild type strain and of mutant strains selected, an alcohol fermentation was carried out using 100 g/l soluble starch. Mutant strain M-9 did not improve the direct alcohol fermentation of starch, despite its excellent amylolytic activities performance. On the other hand, mutant strain M-6 produced 37.9 g/l (4.8%, v/v) ethanol by utilizing about 82% of substrate.