The differential response of thePbenpromoter ofPseudomonas putidamt-2 to BenR and XylS prevents metabolic conflicts inm-xylene biodegradation

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SummaryPseudomonas putidamt-2 encompasses two alternative and potentially conflicting routes for benzoate metabolism, onemetapathway encoded byxylgenes of the pWW0 plasmid and mastered by thePmpromoter and XylS, and one chromosomally encodedorthopathway initiated byPbenand the BenR protein. Any cross-activation ofPbenpromoter by XylS ought to cause a metabolic conflict during the degradation ofm-xylene because 3-methylbenzoate (3MBz) generated as an intermediate can be channelled through theorthopathway and produce toxic dead-end metabolites. The activation ofPbenby XylS was revisited using both reporter technology and tiling arrays targeted to the sequences of interest around messenger RNA initiation of bothPbenandPmpromoters. Analysis of supersensitiveluxCDABEfusions, inspection ofxylXversusbenAtranscripts and growth tests ofbenRmutants indicated that the natural expression ranges of XylS under various conditions are insufficient to cause a significant cross-regulation ofPbenwhether cells face endogenous or exogenous 3MBz. This seems to stem from the nature of the operators for binding either transcriptional factor, which in the case of thePbenpromoter ofP. putidamt-2 appear to have evolved for avoiding a strong interaction with XylS.

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