Miki Ito

Nara Women's University, Nara, Nara, Japan

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Publications (4)10.59 Total impact

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    ABSTRACT: Aquiring new genetic traits by lateral gene transfer is a bacterial strategy for environment adaptation. We previously showed that Escherichia coli could laterally transmit non-conjugative plasmids in co-cultures containing strains with and without the plasmid. In this study, using the Keio collection, a comprehensive library of E. coli knock-out mutants for non-essential genes, we screened for genes responsible for repressing cell-to-cell plasmid transfer in recipient cells. By stepwise screening, we identified 55 'transfer-up' mutants that exhibited approximately 2- to 30-fold increased activities. We confirmed plasmid acquisition by these 'up' mutants and revealed that there were no significant changes in antibiotic resistance in the original Keio strains. The presumed functions of these gene products covered a wide range of activities, including metabolism and synthesis, transport, transcription or translation and others. Two competence-gene homologues (ybaV and yhiR) were identified from among these genes. The presumed localizations of these 55 gene products were estimated to be 34 cytoplasmic proteins, 20 in or around the cell surface and 1 unknown location. Our results suggest that these 55 genes may be involved in repressing plasmid uptake during cell-to-cell plasmid transfer.
    Biochemical and Biophysical Research Communications 11/2012; · 2.41 Impact Factor
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    ABSTRACT: Acquisition of new genetic traits by horizontal gene transfer is a bacterial strategy for adaptation to the environment. We previously showed that Escherichia coli can transmit non-conjugative plasmids laterally in a co-culture containing strains with and without the plasmid. In this study, using the Keio collection, a comprehensive library of E. coli knock-out mutants for non-essential genes, we screened for genes responsible for the execution and promotion of cell-to-cell plasmid transfer in recipient cells. By stepwise screening of 'transfer-down' mutants, two essential genes and six promoting genes were obtained. One of the essential genes was priA, which is involved in DNA replication. This priA mutant was also unable to be transformed by artificial transformation methods, probably due to the deficiency of the plasmid maintenance function. The other essential gene was rodZ (yfgA), a gene involved in the regulation of rod-shaped structure of E. coli cells. This rodZ mutant was transformable by all three methods of artificial transformation tested, suggesting that this gene is essential for cell-to-cell plasmid transfer but not for artificial transformation. These are the first data that suggest that rodZ plays an essential role in DNA acquisition.
    Biochemical and Biophysical Research Communications 04/2012; 421(1):119-23. · 2.41 Impact Factor
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    ABSTRACT: Escherichia coli is not assumed to be naturally transformable. However, several recent reports have shown that E. coli can express modest genetic competence in certain conditions that may arise in its environment. We have shown previously that spontaneous lateral transfer of non-conjugative plasmids occurs in a colony biofilm of mixed E. coli strains (a set of a donor strain harbouring a plasmid and a plasmid-free recipient strain). In this study, with high-frequency combinations of strains and a plasmid, we constructed the same lateral plasmid transfer system in liquid culture. Using this system, we demonstrated that this lateral plasmid transfer was DNase-sensitive, indicating that it is a kind of transformation in which DNase-accessible extracellular naked DNA is essential. However, this transformation did not occur with purified plasmid DNA and required a direct supply of plasmid from co-existing donor cells. Based on this feature, we have termed this transformation type as 'cell-to-cell transformation'. Analyses using medium conditioned with the high-frequency strain revealed that this strain released a certain factor(s) that promoted cell-to-cell transformation and arrested growth of the other strains. This factor is heat-labile and protease-sensitive, and its roughly estimated molecular mass was between ∼9 kDa and ∼30 kDa, indicating that it is a polypeptide factor. Interestingly, this factor was effective even when the conditioned medium was diluted 10(-5)-10(-6), suggesting that it acts like a pheromone with high bioactivity. Based on these results, we propose that cell-to-cell transformation is a novel natural transformation mechanism in E. coli that requires cell-derived DNA and is promoted by a peptide pheromone. This is the first evidence that suggests the existence of a peptide pheromone-regulated transformation mechanism in E. coli and in Gram-negative bacteria.
    PLoS ONE 01/2011; 6(1):e16355. · 3.73 Impact Factor
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    ABSTRACT: We tested the possibility of nonconjugative lateral DNA transfer in a colony biofilm of mixed Escherichia coli strains. By simply coculturing a plasmid-free F(-) strain and another F(-) strain harboring a nonconjugative plasmid in a colony biofilm on antibiotic-free agar media, transformed cells were produced within 24-48 h at the frequency of 10(-10)-10(-9) per recipient cell. PCR analysis of the transformed cells demonstrated the occurrence of lateral plasmid transfer. These cells survived until at least day 7 under antibiotic-free conditions. Liquid cultures of the same strains in Luria-Bertani broth produced no or few transformants, suggesting the importance of colony-biofilm formation for plasmid transfer. This is a novel line of evidence indicating that nonconjugative, nonviral horizontal gene transfer can occur between E. coli cells.
    FEMS Microbiology Letters 03/2006; 255(1):115-20. · 2.05 Impact Factor

Publication Stats

31 Citations
10.59 Total Impact Points

Institutions

  • 2011–2012
    • Nara Women's University
      • • Graduate School of Humanities and Sciences
      • • Faculty of Human Life and Environment
      Nara, Nara, Japan