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    A widely conserved molecular switch controls quorum sensing and symbiosis island transfer in Mesorhizobium loti through expression of a novel antiactivator

    Access Status
    Fulltext not available
    Authors
    Ramsay, Joshua
    Major, A.
    Komarovsky, V.
    Sullivan, J.
    Dy, R.
    Hynes, M.
    Salmond, G.
    Ronson, C.
    Date
    2013
    Type
    Journal Article
    
    Metadata
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    Citation
    Ramsay, Joshua P. and Major, Anthony S. and Komarovsky, Victor M. and Sullivan, John T. and Dy, Ron L. and Hynes, Michael F. and Salmond, George P.C. and Ronson, Clive W. 2013. A widely conserved molecular switch controls quorum sensing and symbiosis island transfer in Mesorhizobium loti through expression of a novel antiactivator. Molecular Microbiology. 87 (1): pp. 1-13.
    Source Title
    Molecular Microbiology
    DOI
    10.1111/mmi.12079
    ISSN
    0950382X
    URI
    http://hdl.handle.net/20.500.11937/32760
    Collection
    • Curtin Research Publications
    Abstract

    ICEMlSymR7A of Mesorhizobium loti is an integrative and conjugative element (ICE) that confers the ability to form a nitrogen-fixing symbiosis with Lotus species. Horizontal transfer is activated by TraR and N-acyl-homoserine lactone (AHL), which can stimulate ICE excision in 100% of cells. However, in wild-type cultures, the ICE is excised at low frequency. Here we show that QseM, a widely conserved ICE-encoded protein, is an antiactivator of TraR. Mutation of qseM resulted in TraR-dependent activation of AHL production and excision, but did not affect transcription of traR. QseM and TraR directly interacted in a bacterial two-hybrid assay in the presence of AHL. qseM expression was repressed by a DNA-binding protein QseC, which also activated qseC expression from a leaderless transcript. QseC differentially bound two adjacent operator sites, the lower affinity of which overlapped the -35 regions of the divergent qseCqseM promoters. QseC homologues were identified on ICEs, TraR/TraM-regulated plasmids and restriction-modification cassettes, suggesting a conserved mode of regulation. Six QseC variants with distinct operators were identified that showed evidence of reassortment between mobile elements. We propose that QseC and QseM comprise a bimodal switch that restricts quorum sensing and ICEMlSymR7A transfer to a small proportion of cells in the population.

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