The pWW0 plasmid imposes a stochastic expression regime to the chromosomal ortho pathway for benzoate metabolism in Pseudomonas putida

Authors

  • Rafael Silva-Rocha,

    1. Systems Biology Program, Centro Nacional de Biotecnología CSIC, Cantoblanco-Madrid, Spain
    Current affiliation:
    1. FMRP – University of São Paulo, Ribeirao Preto, SP, Brazil
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  • Victor de Lorenzo

    Corresponding author
    1. Systems Biology Program, Centro Nacional de Biotecnología CSIC, Cantoblanco-Madrid, Spain
    • Correspondence: Víctor de Lorenzo, Centro Nacional de Biotecnología-CSIC, Campus de Cantoblanco, Madrid 28049, Spain. Tel.: 34 91 585 45 36; fax: 34 91 585 45 06; e-mail: vdlorenzo@cnb.csic.es

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Abstract

Environmental plasmids often expand the metabolic repertoire of bacteria that carry them, but they also interfere with the biochemical and genetic network of the host. The pWW0 plasmid born by Pseudomonas putida mt-2 encodes the TOL pathway for degradation of toluene/m-xylene through production of intermediate compounds benzoate/3-methylbenzoate. These can be also recognized as substrates by the chromosomally encoded ben and cat gene products, thereby creating a manifest regulatory and biochemical conflict. In this context, we have investigated how the introduction of the pWW0 plasmid into P. putida affects behaviour of the promoter of the ben pathway (Pb) in single cells. Using a series of standardized transcriptional fusions to green fluorescent protein, we found that acquisition of the TOL pathway switches the activation course of the Pb promoter from unimodal/graded to bimodal/stochastic when cells were exposed to benzoate. This behaviour was propagated downstream into the Pc promoter of the cat gene cluster, which responds to the benzoate-degradation intermediate cis,cis-muconate. The TOL plasmid thus imposes expression of the chromosomal Pb with a stochastic behaviour likely to result in biochemical heterogeneity of the otherwise genetically clonal population when exposed to benzoate as a growth substrate.

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