• Korean Journal of Veterinary Research
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• v.39 no.2
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• pp.327-337
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• 1999

The transposon TnphoA was used to generate avirulent mutants from a type A Pasteurella multocida. A suicide vector plasmid pRT733 carrying TnphoA, having the kanamycin resistant gene and harbored in Escherichia coli K-12 strain SM10(${\lambda}pir$), was mated with streptomycin resistant P. multocida P-1059 strain as recipient. This resulted in the generation of two TnphoA insertion mutants (transconjugants, tc95-a and tc95-b) which were resistant both to kanamycin ($Km^{R}$) and streptomycin ($Sm^{R}$), secreted alkaline phosphatase, and were avirulent to turkeys. Southern blot hybridization using two probes derived from internal fragments of TnphoA, confirmed the insertion of TnphoA into 12.9kb or 13.7kb DNA fragment from the EcoRV digested genomic fragments of transconjugants. The two transconjugants, tc95-a and tc95-b, were distinguishable from their parent strains by differences in ribotypes, and outer membrane protein profiles. TnphoA insertion in both transconjugants also resulted in constitutive expression of a 33Kd iron regulated outer membrane protein (IROMP). The gene encoding $Sm^{R}$ was also located within the same 12.9kb EcoRV genomic fragment from both transconjugants. Furthermore, our finding that the recipient P. multocida P-1059 $Sm^{R}$ strain and both transconjugants were avirulent to turkeys suggest that the either 12.9kb or 13.7kb genomic DNA contains the virulence gene and speculate that the presence of $Sm^{R}$ gene or TnphoA insertion may be responsible for regulating and inactivating the gene(s) encoding virulence in P. multocida.

• Journal of Microbiology
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• v.45 no.4
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• pp.339-343
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• 2007

Methylglyoxal (MG) is a reactive metabolite known to accumulate in certain physiological conditions. We attempted to isolate genes associated with this metabolite by genome-wide mutagenesis with TnphoA derivative. After screening on methylglyoxal-containing plate, we obtained insertions in three different genes, ydbD, yjjQ, and yqiI, which gave rise to reproducible MG-sensitive phenotypes in glyoxalase-deficient strain. In addition to its MG sensitivity, the insertion in yqiI exhibited an impaired motility resulting from a reduced flagellar expression.

• Journal of Microbiology and Biotechnology
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• v.17 no.8
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• pp.1344-1352
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• 2007

An opportunistic human pathogen, Pseudomonas aeruginosa, contains the major catalase KatA, which is required to cope with oxidative and osmotic stresses. As an attempt to uncover the $H_2O_2$-dependent regulatory mechanism delineating katA gene expression, four prototrophic $H_2O_2$-sensitive mutants were isolated from about 1,500 TnphoA mutant clones of P. aeruginosa strain PA14. Arbitrary PCR and direct cloning of the transposon insertion sites revealed that one insertion is located within the katA coding region and two are within the coding region of oxyR, which is responsible for transcriptional activation of several antioxidant enzyme genes in response to oxidative challenges. The fourth insertion was within PA3815 (IscR), which encodes a homolog of the Escherichia coli iron-sulfur assembly regulator, IscR. The levels of catalase and SOD activities were significantly reduced in the iscR mutant, but not in the oxyR mutant, during the normal planktonic culture conditions. These results suggest that both IscR and OxyR are required for the optimal resistance to $H_2O_2$, which involves the expression of multiple antioxidant enzymes including KatA.

• Journal of Microbiology and Biotechnology
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• v.18 no.6
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• pp.1040-1043
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• 2008

Klebsiella oxytoca CCUG 15788 is resistant to $Ni^{2+}$ at a concentration of 10 mM and grows in an inducible manner when exposed to lower concentrations of $Ni^{2+}$. The complete genomic sequence of a 4.2-kb HindIII-digested fragment of this strain was determined from genomic DNA. It was shown to contain four nickel resistance genes (nirA, nirB, nirC, and nirD) encoding transporter and transmembrane proteins for nickel resistance. When the plasmid pKOHI4, encoding nirABCD, was transformed into Escherichia coli JM109, the cells were able to grow in Tris-buffered mineral medium containing 3 mM nickel. TnphoA'-1 insertion mutants in the four nickel genes nirA, nirB, nirC, and nirD showed nickel sensitivity. The nir genes were heterogeneously expressed in E. coli, suggesting functional roles of these genes in nickel resistance.

• Journal of Microbiology and Biotechnology
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• v.15 no.6
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• pp.1214-1220
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• 2005

Decreased porin-mediated outer membrane penetration of hydrophilic antibiotics is a common mechanism of antibiotic resistance in Gram-negative bacteria. This study was undertaken to determine whether a null mutation in Pseudomonas putida would suppress porin synthesis, and therefore reduce the susceptibility of the organism to streptomycin, norfloxacin, and tetracycline. Inverse PCR amplification and double-stranded DNA sequencing were used to identify chromosomal genes carrying TnphoA'-1 inserts. Genome database available was used to identify putative homologue genes, one of which encodes protein with homology to domains of the MutS of P. putida, suggesting a crucial role in the multidrug resistance. Increased resistance to streptomycin, norfloxacin, and tetracycline might be due to accumulation of compensatory mutations. Either no growth or slow growth was observed in P. putida KH1027 when grown in minimal medium containing gluconate, glucose, or citrate; however, it is not clear whether the growth patterns contributed to the multidrug resistance.