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Inhibition of Bacillus subtilis natural competence by a native, conjugative plasmid-encoded comK repressor protein

Authors

  • Praveen K. Singh,

    1. Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain.
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  • Gayetri Ramachandran,

    1. Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain.
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  • Lucía Durán-Alcalde,

    1. Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain.
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  • Carlos Alonso,

    1. Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain.
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  • Ling Juan Wu,

    Corresponding author
    1. Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle Upon Tyne NE2 4AX, UK.
      E-mail l.j.wu@newcastle.ac.uk; Tel. (+44) 191  208 3231; Fax (+44) 191 208 3205;
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  • Wilfried J. J. Meijer

    Corresponding author
    1. Centro de Biología Molecular ‘Severo Ochoa’ (CSIC-UAM), Instituto de Biología Molecular ‘Eladio Viñuela’ (CSIC), Universidad Autónoma, Canto Blanco, 28049 Madrid, Spain.
      E-mail wmeijer@cbm.uam.es; Tel. (+34) 91 196 4515; Fax (+34) 91 196 4420.
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E-mail l.j.wu@newcastle.ac.uk; Tel. (+44) 191  208 3231; Fax (+44) 191 208 3205;

E-mail wmeijer@cbm.uam.es; Tel. (+34) 91 196 4515; Fax (+34) 91 196 4420.

Summary

Under certain growth conditions, Bacillus subtilis can develop natural competence, the state in which it is able to bind, adsorb and incorporate exogenous DNA. Development of competence is a bistable process and is subject to complex regulation. Rok is a repressor of the key transcriptional activator of competence genes, comK, and limits the size of the subpopulation that develops competence. Here we report the finding that the large conjugative B. subtilis plasmid pLS20 harbours a rok homologue rokLS20. Although the deduced product of rokLS20 is considerably shorter than the chromosomally encoded Rok protein, we show that ectopic expression of the plasmid-encoded RokLS20 leads to inhibition of competence by repressing comK, and that the effects of the plasmid and chromosomally encoded Rok proteins are additive. We also show that pLS20 inhibits competence in a rokLS20-dependent manner and that purified RokLS20 preferentially binds to the comK promoter. By analysing the available databases we identified several additional rok-like genes. These putative rok genes can be divided into two groups and we propose that rokLS20 is the prototype of a newly identified subgroup of nine rok genes. Finally, we discuss the possible role of the plasmid-located rok and its relatedness with other rok genes.

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