• Journal of Life Science
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• v.9 no.2
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• pp.146-152
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• 1999

In order to elucidate a role of residue 24 in the folding of tryptophan synthase $\alpha$ subunit, mutant proteins in which Thr 24 was replaced by Met, Ala, Ser, Leu or Lys were overexpressed in E. coli, and the extents of accumulated proteins as soluble or aggregated forms were examined. The mutant proteins with Met or Leu at residue 24 were predominantly accumulated as soluble forms as the native protein. On the other hand, mutant proteins with Ser, Ala or Lys at residue 24 were expressed as aggregated forms as well. This result suggests that residue 24 of tryptophan synthase $\alpha$ subunit may be implicated in the folding of this protein.

• Applied Biological Chemistry
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• v.4
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• pp.11-16
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• 1963

(1) The 30 strains of Penicillia and the 52 strains of Aspergilli have been screened for their producibility of 5'-Phosphodiesterase, and Penicillium sclerotiorum 7321, Penicillium sp M-11 and Penicillium citrinum UV-mutant 2032-72 were selected as having high 5‘-Phosphodiesterase activity. (2) Using the wheat bran medium the 5‘-Phosphodiesterase production was reached at maximum state by the plate culture for 10 days at $30^{\circ}C$ (3) The optimum conditions of the 5'-Phosphodiesterase activity of Penicillium sclerotiorum 7321 and Penicillium sp M-11 were pH 4.0 at $62.5^{\circ}C$, while the optimum condition of the 5'-Phosphodiesterase activity of Penicillium citrinum UV-mutant 2032-72 was pH 5.0 at $50^{\circ}C$.

• Journal of Microbiology and Biotechnology
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• v.20 no.4
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• pp.718-726
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• 2010

A selected fungal strain, for production of the raw-starchdigesting enzyme by solid-state fermentation, was improved by two repeated sequential exposures to ${\gamma}$-irradiation of $Co^{60}$, ultraviolet, and four repeated treatments with Nmethyl-N'-nitrosoguanidine. The mutant strain Aspergillus sp. XN15 was chosen after a rigorous screening process, with its production of the raw-starch-digesting enzyme being twice that of usual wild varieties cultured under preoptimized conditions and in an unsupplemented medium. After 17 successive subculturings, the enzyme production of the mutant was stable. Optimal conditions for the production of the enzyme by solid-state fermentation, using wheat bran as the substrate, were accomplished for the mutant Aspergillus sp. XN15. With the optimal fermentation conditions, and a solid medium supplemented with nitrogen sources of 1% urea and 1% $NH_4NO_3$, 2.5 mM $CoSO_4$, 0.05% (v/w) Tween 80, and 1% glucose, the mutant Aspergillus sp. XN15 produced the raw-starch-digesting enzyme in quantities 19.4 times greater than a typical wild variety. Finally, XN15, through simultaneous saccharification and fermentation of a raw rice corn starch slurry, produced a high level of ethanol with $Y_{p/s}$ of 0.47 g/g.

• Journal of Microbiology and Biotechnology
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• v.18 no.9
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• pp.1518-1521
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• 2008

Bacteria sense their population density and coordinate the expression of target genes, including virulence factors in Gram-negative bacteria, by the N-acylhomoserine lactones (AHLs)-dependent quorum sensing (QS) mechanism. In contrast, several soil bacteria are able to interfere with QS by enzymatic degradation of AHLs, referred to as quorum quenching. A potent AHL-degrading enzyme, AiiA, from Bacillus thuringiensis has been reported to effectively attenuate the virulence of bacteria by quorum quenching. However, little is known about the role of AiiA in B. thuringiensis itself. In the present study, an aiiA-defective mutant was generated to investigate the role of AHA in rhizosphere competence in the root system of pepper. The aiiA mutant showed no detectable AHL￢-egrading activity and was less effective for suppression of soft-rot symptom caused by Erwinia carotovora on the potato slice. On the pepper root, the survival rate of the aiiA mutant significantly decreased over time compared with that of wild type. Interestingly, viable cell count analysis revealed that the bacterial number and composition of E. carotovora were not different between treatments of wild type and the aiiA mutant. These results provide evidence that AHA can play an important role in rhizosphere competentce of B. thuringiensis and bacterial quorum quenching to Gram-negative bacteria without changing bacterial number or composition.

• Korean Journal of Environmental Biology
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• v.22 no.4
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• pp.487-493
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• 2004

To investigate the antifungal activity related protein in pesticidal bacteria, a bacterial strain LTD was isolated from soil collected at Gimje in Jeonbuk province, Korea, and identified as Bacillus subtilis LTD based on a API50 CHB kit and 168 rDNA sequencing. It has an antifungal activity against 9 plant pathogenic fungi in a paper disc assay. The antifungal activity- deficient mutant, B. subtilis mLTD was induced at a 5 kGy dose of $^{60}Co$ gamma radiation. Using the two-dimensional electrophoresis and the matrix assisted laser desorption ionization time-of-flight mass spectrometry, the comparison analysis of proteins between the wild and mutant were performed. A major intracellular serine proteinase IspA (MW: 32.5 kDa), a NAD (P) H dehydrogenase (MW: 20.0 kDa), and a stage II sporulation protein AA, SpoIIAA (MW: 14.3kDa) were detected only in the B. subtilis LTD. These results suggested that the functions of these proteins found only in the B. subtilis LTD could. be closely related to the antifungal activity against plant pathogenic fungi.

• Korean Journal of Microbiology
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• v.20 no.4
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• pp.173-182
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• 1982

From FGSC 159 strain of Aspergillus nidulans, temperature sensitive mutants that are defective in growth and differentiation have been isolated by N-methyl-N'-nitroN-nitrosoguanidine (NTG) treatment. The optimum concentration of NTG and incubation time to get the highest mutation frequency was $100{\mu}g$ per ml and 1 hour, respectively. The survival frequency was 1%. Among the isolated mutants, five strains that were affected in early steps of differentiation were selected for further studies and named smK, smY, smB, smF, and smZ. The execution point of each mutant was determined and the growing pattern of each mutant at the restrictive temperature was observed under the microscope. Growth of mutant was arrested near at the execution point. From genetic analysis, each temperature-sensitive mutants was thought to have a single recessive gene. The genes of smK, smY, smB, smF, and smZ are linked to the chromosome VII, IV, VIII, I, and VI, respectively. It can be concluded that the genes controlling the differentiation are widely dispersed in the genome. From the results of mutant, smK, it is considered that a single gene can affect a function (functions) which act(s) at two different steps during differentiation.

• BMB Reports
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• v.37 no.1
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• pp.122-132
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• 2004

The rapid development and characterization of the mouse genome sequence, coupled with comparative sequence analysis of human, has been paralleled by a reinforced enthusiasm for mouse functional genomics. The way to uncover the in vivo function of genes is to analyze the phenotypes of the mutant animals. From this standpoint, the mouse is a suitable and valuable model organism in the studies of functional genomics. Therefore, there have been enormous efforts to enrich the list of the mutant mice. Such a trend emphasizes the random mutagenesis, including ENU mutagenesis and gene-trap mutagenesis, to obtain a large stock of mutant mice. However, since various mutant alleles are needed to precisely characterize the role of a gene in vivo, mutations should be designed. The simplicity and utility of transgenic technology can satisfy this demand. The combination of RNA interference with transgenic technology will provide more opportunities for researchers. Nevertheless, gene targeting can solely define the in vivo function of a gene without a doubt. Thus, transgenesis and gene targeting will be the major strategies in the field of functional genomics.

• Korean Journal Plant Pathology
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• v.10 no.3
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• pp.151-156
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• 1994

Pseudomonas fluorescens produces the antibiotic, 2,4-diacetylphloroglucinol (Phl), which promotes plant growth by inhibiting bacteria and fungi. Cosmids (genomic library) were mobilized into Phl-nonproducing mutants through the triparental matings with pRK2013 as the helper plasmid at the frequency of 8.37$\times$10-4. Complemented mutants that showed antibiotic activity were selected among about 2,000 transconjugants. The complemented mutants were confirmed by acquired drug resistances (kanamycin and tetracycline). The antibiotic substances of wild type and complemented mutants showed the most excellent anti-bacterial activity. Inhibitory effects of complemented P. fluorescens against phytopathogenic fungi were equal to the parental strain. Complemented mutant and wild type of P. fluorescens were causal microbes of fungal morphological abnormalities. Complemented mutants in potato dextrose agar supplemented with bromothymol blue also showed restoration of glucose utilization as wild type. Plasmids of complemented mutants were isolated from transconjugant sand transformed into competent cells of E. coli DH5$\alpha$. The plamid DNA was reisolated from transformed E. coli DH5$\alpha$.

• Journal of Microbiology and Biotechnology
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• v.16 no.8
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• pp.1174-1179
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• 2006

The wild-type Corynebacterium glutamicum ATIC 13032 and Corynebacterium glutamicum ATTC 13032 lysC S301Y, exhibiting a deregulated aspartokinase, were compared concerning growth, lysine production, and intracellular carbon fluxes. Both strains differ by only one single nucleotide over the whole genome. In comparison to the wild-type, the mutant showed significant production of lysine with a molar yield of 0.087 mol (mol glucose$^{-1}$) whereas the biomass yield was reduced. The deregulation of aspartokinase further led to a global rearrangement of carbon flux throughout the whole central metabolism. This involved an increased flux through the pentose phosphate pathway (PPP) and an increased flux through anaplerosis. Because of this, the mutant revealed an enhanced supply of NADPH and oxaloacetate required for lysine biosynthesis. Additionally, the lumped flux through phosphoenolpyruvate carboxykinase and malic enzyme, withdrawing oxaloacetate back to the glycolysis and therefore detrimental for lysine production, was increased. The reason for this might be a contribution of malic enzyme to NADPH supply in the mutant in the mutant. The observed complex changes are remarkable, because they are due to the minimum genetic modification possible, the exchange of only one single nucleotide.

• Microbiology and Biotechnology Letters
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• v.29 no.1
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• pp.12-17
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• 2001

Aspergil-lus coreanus NR-15 and Aspergilus oryzae NR-2-5 from traditional Korean Nuruk were selected as parental strains producing starch hydrolysis enzyme. Xll(Arginine-) mutant from A. coreanus NR 15-1 showed high glu-doamylase activity and total acid productivity. Z6(Adenine-) mutant from A. oryzae NR2-5 showed the highest $\alpha$-amylase activity. Therefore, both XII and Z6 mutants were selected and investigated for the optimal conditions of protoplast formation for protoplast fusion. Mixture of equal amount of cellulase and driselase(10mg/ml each) was the most effective as lytic enzymes. The optimal pH and temperature for protoplast formation were 5.0 and $30^{\circ}C$, respectively. The most effective reaction for protoplast formation time was 4 hours. The maximum of protoplst for- mation of Xll mutant and Z6 mutant were $6.54$\times$10^{7}$ protoplasts/ ml and $3.04$\times$10^{ 7}$ protoplasts/ml, and the regen-eration frequencies of the protoplasts were 11.3% and 11.6%, respectively. The size of the protoplasts from X11 and Z6 mutants were 3~6 $\mu\textrm{m}$ and 4~9$\mu\textrm{m}$, respectively.