Growth phase-dependent transcription of the sigma(54)-dependent Po promoter controlling the Pseudomonas-derived (methyl)phenol dmp operon of pVI150

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Abstract
Transcription from Pseudomonas-derived -24, -12 Po promoter of the pVI150-encoded dmp operon is mediated by the sigma 54-dependent DmpR activator in response to the presence of aromatic pathway substrates in the medium. However, global regulatory mechanisms are superimposed on this regulatory system so that the specific response to aromatic effectors is absent in cultures until the stationary phase is reached. Here we genetically dissect the system to show that the growth phase response is faithfully mimicked by a minimal system composed of the dmpR regulatory gene and the Po promoter regulatory region and can be reproduced in heterologous Escherichia coli. Using this system, we show that the growth phase-dependent DmpR-mediated response to aromatic compounds is limited to fast-growing cultures. Thus, during exponential growth of cultures in minimal media containing different carbon sources, the response to aromatics is immediate, while the response is suppressed in cultures grown on rich media until the exponential-to-stationary phase transition. Elements known to be involved in the DmpR-mediated transcription from Po were analyzed for the ability to influence the growth phase response. Most dramatically, overexpression of DmpR was shown to completely abolish the growth phase response, suggesting that a negatively acting factor may mediate this level of regulation. The possible mechanism of action and integration (of the specific regulation of the dmp operon-encoded catabolic enzymes with the physiological status of the bacteria are discussed.