Transcriptional induction kinetics from the promoters of the catabolic pathways of TOL plasmid pWW0 of Pseudomonas putida for metabolism of aromatics

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Abstract
We determined, under several growth conditions, the kinetics of mRNA synthesis from the four Pseudomonas putida pWW0 plasmid promoters involved in degradation of xylenes and methylbenzyl alcohols via toluates. Transcription by XylS of the meta-cleavage pathway operon promoter (Pm) for the metabolism of alkylbenzoates was stimulated immediately after the addition of an effector, both in Luria-Bertani (LB) medium and in minimal medium. Activation of the sigma 54-dependent upper-pathway operon promoter (Pu) and the xylS gene promoter (Ps) by effector-activated XylR was dependent on the growth medium used: on minimal medium, activation of transcription from Pu and Ps occurred immediately after the addition of a XylR effector; in contrast, activation appeared only after several hours when cells were growing on LB medium. When Pm was induced through the physiological overexpression of XylS, mediated by XylR when this regulator was activated by upper-pathway effectors, the kinetics of transcription from Pm was similar to that of Pu and Ps: maximum values were reached after delays of several hours in rich medium and after several minutes in minimal medium. The delay in the induction of transcription of sigma 54-dependent promoters reflects catabolite inhibition exerted by LB components, since the addition of yeast extracts, Casamino Acids, or several combinations of amino acids dramatically inhibited the synthesis of XylR-controlled sigma 54-dependent promoters. Expression from xylR gene tandem promoters occurred independently of the growth medium used.

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