Stochasticity of TOL plasmid catabolic promoters sets a bimodal expression regime in Pseudomonas putida mt-2 exposed to m-xylene.

Rafael Silva-Rocha, Víctor de Lorenzo

Systems Biology Program, Centro Nacional de Biotecnología CSIC, Cantoblanco-Madrid 28049, Spain.

Molecular microbiology 2012 Oct

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The expression dynamics of the catabolic promoters of the TOL plasmid pWW0 has been examined in single cells of Pseudomonas putida mt-2 exposed to m-xylene. To this end, we employed an á la carte bi-cistronic gfp-lacZ reporter system for generating monocopy transcriptional fusions to each of the four promoters (Pr, Ps, Pu and Pm) of the regulatory network. Whereas expression of xylR (the master regulatory gene of the TOL system) behaved in a unimodal fashion, the activation of Pu and Pm displayed a high degree of stochasticity. This event resulted in a time-dependent shift in the bacterial population between two induction states without intermediate expression levels. Bimodality of the Pm promoter for the lower TOL pathway was largely due to the propagation of the Ps output throughout the network, which caused stochastic overproduction of the second regulator of the system, XylS. Surprisingly, activation of Pm by the form of XylS that was bound to the pathway intermediate 3-methylbenzoate was relatively minor. These stochastic phenomena in response to m-xylene disappeared in the stationary phase. Taken together, the data suggests that genetically homogeneous populations of P. putida mt-2 employ a strategy of phenotypic variation (metabolic bet-hedging) when confronted with mixtures of nutrients. © 2012 Blackwell Publishing Ltd.

Citation

Rafael Silva-Rocha, Víctor de Lorenzo. Stochasticity of TOL plasmid catabolic promoters sets a bimodal expression regime in Pseudomonas putida mt-2 exposed to m-xylene. Molecular microbiology. 2012 Oct;86(1):199-211