• The Plant Pathology Journal
• /
• 제25권3호
• /
• pp.205-212
• /
• 2009

Colletotrichum acutatum was the main cause of the recent outbreaks of anthracnose on pepper fruit in Korea. To facilitate molecular analysis of C. acutatum, we generated an arginine auxotrophic mutant of the C acutatum strain JC24 using a targeted gene replacement strategy. A 3.3-kb genomic region carrying an ortholog (designated CaARG2) of the fungal gene encoding N-acetylglutamate synthase, the first enzyme of arginine biosynthesis in fungi, was deleted from the fungal genome. The mutant exhibited normal growth only when arginine was exogenously supplied into the culture medium. Transformation of the arginine auxotrophic mutant with a plasmid DNA carrying an intact copy of CaARG2, which was smaller than the deleted region in the mutant, not only caused random vector insertions in the fungal genome, but also recovered both hyphal growth and pathogenicity of the mutant to the wild-type level. Using this new selection system, we have successfully developed a restriction enzyme-mediated integration procedure, which would provide an economically efficient random mutagenesis method in C. acutatum.

• 한국미생물·생명공학회지
• /
• 제26권5호
• /
• pp.393-399
• /
• 1998

고추역병균(Phytophthora capsici)의 성장을 in vitro에서 저해하는 길항균 Bl4를 한국토양으로부터 분리 동정하여 Enterobacter속임을 밝혔고 Pl::Tn5 lac에 의해 transposon돌연변이를 유기하여 길항력 강화주와 약화주들의 염색체내에 Tn5 lac이 각기 상이한 위치에 무작위로 삽입되었음을 southern hybridization에 의해 확인하였다.

• Journal of Microbiology and Biotechnology
• /
• 제19권3호
• /
• pp.217-228
• /
• 2009

Mobile genetic segments, or transposons, are also referred to as jumping genes as they can shift from one position in the genome to another, thus inducing a chromosomal mutation. According to the target site-specificity of the transposon during a transposition event, the result is either the insertion of a gene of interest at a specific chromosomal site, or the creation of knockout mutants. The former situation includes the integration of conjugative transposons via site-specific recombination, several transposons preferring a target site of a conserved AT-rich sequence, and Tn7 being site-specifically inserted at attTn7, the downstream of the essential glmS gene. The latter situation is exploited for random mutagenesis in many prokaryotes, including IS (insertion sequence) elements, mariner, Mu, Tn3 derivatives (Tn4430 and Tn917), Tn5, modified Tn7, Tn10, Tn552, and Ty1, enabling a variety of genetic manipulations. Randomly inserted transposons have been previously employed for a variety of applications such as genetic footprinting, gene transcriptional and translational fusion, signature-tagged mutagenesis (STM), DNA or cDNA sequencing, transposon site hybridization (TraSH), and scanning linker mutagenesis (SLM). Therefore, transposon-mediated genetic engineering is a valuable discipline for the study of bacterial physiology and pathogenesis in living hosts.

• Journal of Microbiology and Biotechnology
• /
• 제16권6호
• /
• pp.974-978
• /
• 2006

The cytochrome P450 monooxygenase from the pikromycin biosynthetic gene cluster in Streptomyces venezuelae, known as PikC, was observed to hydroxylate the unnatural substrate indole to indigo. Furthermore, the site-directed mutagenesis of PikC monooxygenase led to the mutant enzyme F171Q, in which Phe171 was altered to Gln, with enhanced activity for the hydroxylation of indole. From enzyme kinetic studies, F171Q showed an approximately five-fold higher catalytic efficiency compared with the wild-type PikC. Therefore, these results demonstrate the promising application of P450s originating from Streptomyces, normally involved in polyketide biosynthesis, to generate a diverse array of other industrially useful compounds.

• Preventive Nutrition and Food Science
• /
• 제6권1호
• /
• pp.79-81
• /
• 2001

Deoxynucleoside kinases exist as heterodimeric pairs specific for deoxyadenosine/deoxyguanosine kinase (dAK/dGK) and deoxyadenosine/deoxycytidine kinase (dAK/dCK). The aspartic acid-84 in dGK was mutated to alanine, asparagine and glutamic acid by site-directed mutagenesis. The mutation resulted in a drastic decease in dGK activity compared to the unmodified cloned enzyme while it increased production of dAK activity. The mutated dak/dgk genes, which synthesize tandem deoxyadenosine/deoxyguanosine kinase, were inserted back to the Lactobacillus acidophilus and Lactococcus lactis by electroporation to determine the effect of site-directed mutation of he enzymes on the microbial growth. However, no significant change was observed in cell growth and lactic acid production between wild type and mutant lactic acid bacteria.

• 자연과학논문집
• /
• 제9권1호
• /
• pp.45-52
• /
• 1997

저농도의 MNNG가 Aspergillus nidulans의 생존도 및 돌연변이 유발에 끼치는 영향을 조사하였다. Nontoxic하고 submutagenic한 농도의 MNNG 선 처리는 높은 농도로 처리 시의 치사율 및 돌연변이 유발을 낮추지 못했다. 이러한 결과는 Aspergillus nidulans에는 MNNG 에 의한 adaptive response가 일어나지 않는다는 것을 시사하고 있다. 발아 과정의 첫 번째 체세포 분열에서, 시간별로 MNNG에 대한 치사율을 조사하고 UV에 의한 생존도와 비교하였다. UV나 MNNG 처리 시 치사율은 S 세포 시기 직전까지 증가하였다가, DNA 복제 시에는 감소함을 나타내었다. MNNG 처리 시는 UV와 달리 G2세포시기에 치사율이 가장 높았다.

• Journal of Microbiology and Biotechnology
• /
• 제25권1호
• /
• pp.11-17
• /
• 2015

In an attempt to shift the optimal pH of the xylanase B (XynB) from Aspergillus niger towards alkalinity, target mutation sites were selected by alignment between Aspergillus niger xylanase B and other xylanases that have alkalophilic pH optima that highlight charged residues in the eight-residues-longer loop in the alkalophilic xylanase. Multiple engineered XynB mutants were created by site-directed mutagenesis with substitutions Q164K and Q164K+D117N. The variant XynB-117 had the highest optimum pH (at 5.5), which corresponded to a basic 0.5 pH unit shift when compared with the wild-type enzyme. However, the optimal pH of the XynB-164 mutation was not changed, similar to the wild type. These results suggest that the residues at positions 164 and 117 in the eight-residues-longer loop and the cleft's edge are important in determining the pH optima of XynB from Aspergillus niger.

• Journal of Microbiology and Biotechnology
• /
• 제20권3호
• /
• pp.563-568
• /
• 2010

The Val289 residue in the $\alpha$-amylase of Bacillus amyloliquefaciens, which is equivalent to the Ala289 and Val286 residues in the $\alpha$-amylases of B. stearothermophilus and B. licheniformis, respectively, was studied by site-directed mutagenesis. This residue was substituted with 10 different amino acids by random substitution of the Val codon. In these mutant $\alpha$-amylases, Val289 was substituted with Ile, Tyr, Phe, Leu, Gly, Pro, Ser, Arg, Glu, and Asp. Compared with the wild-type $\alpha$-amylase, the mutant $\alpha$-amylase Val289Ile showed 20% more hydrolytic activity, whereas Val289Phe and Val289Leu showed 50% lesser activity. On the other hand, the mutant $\alpha$-amylases Val289Gly, Val289Tyr, Val289Ser, and Val289Pro showed less than 15% activity. The substitution of Val289 with Arg, Asp, or Glu resulted in complete loss of the $\alpha$-amylase activity. Interestingly, the mutant $\alpha$-amylase Val289Tyr had acquired a transglycosylation activity, which resulted in the change of product profile of the reaction, giving a longer oligosaccharide.

• Molecules and Cells
• /
• 제19권3호
• /
• pp.365-374
• /
• 2005

To find potential targets of novel antimicrobial agents, we identified essential genes of Streptococcus pneumoniae using comparative genomics and allelic replacement mutagenesis. We compared the genome of S. pneumoniae R6 with those of Bacillus subtilis, Enterococcus faecalis, Escherichia coli, and Staphylococcus aureus, and selected 693 candidate target genes with > 40% amino acid sequence identity to the corresponding genes in at least two of the other species. The 693 genes were disrupted and 133 were found to be essential for growth. Of these, 32 encoded proteins of unknown function, and we were able to identify orthologues of 22 of these genes by genomic comparisons. The experimental method used in this study is easy to perform, rapid and efficient for identifying essential genes of bacterial pathogens.

• 한국미생물·생명공학회지
• /
• 제14권4호
• /
• pp.271-277
• /
• 1986

Sisomicin 생산균인 Micromonospora inyoensis 균주를 변이유기체로 처리하였을 때 활성이 높은 균주들을 얻기 위한 최적조건으로는 각각 자외선(UV light) 처리에서 90％, nitrosoguanidine(NTG)에 대해 99％, nitrous acid에 대해 99.3％의 사멸율을 나타내는 경우였다. 이 때 분리된 colony들의 sisomicin생성능의 측정은 액체배양 대신 쉽고 간편한 agar plug법을 사용하였다. 한편, 변이유기제로 처리한 후 우량균주를 선택적으로 분리하기 위한 방법으로 aminoglycoside계통의 항생물질 혹은 중금속염을 함유한 농도구배 agar plate에서 생성된 균주들의 화성을 살펴본 결과, 항생물질로서는 gentamicin, kanamycin 이, 중금속염으로서는 Co, Hg가 효과적이었다.