Promoter-creating mutations in <i>Pseudomonas putida</i> : A model system for the study of mutation in starving bacteria

<jats:p> A novel experimental system to study mutation in starving bacteria was designed, relying on the activation of a promoterless phenol degradation operon of <jats:italic>Pseudomonas putida</jats:italic> . The Phe <jats:sup>+</jats:sup> (phenol-utilizing) mutants accumulated in the starving culture of <jats:italic>P. putida</jats:italic> in the presence of phenol but not in the absence of it. We ruled out the possibility that the absence of phenol eliminates Phe <jats:sup>+</jats:sup> mutants from the starving population. Sequence analysis of the Phe <jats:sup>+</jats:sup> mutants revealed that base substitutions, deletions, and insertion of Tn <jats:italic>4652</jats:italic> can result in creation of a sequence similar to the σ <jats:sup>70</jats:sup> -specific promoter consensus. One particular C → A transversion was predominant in the Phe <jats:sup>+</jats:sup> mutants that arose in the starving population under selection for phenol use. In contrast, various deletions were the most frequent Phe <jats:sup>+</jats:sup> mutants occurring in a culture growing without selection. The accumulation rate of the Phe <jats:sup>+</jats:sup> mutants on selective plates was found to be higher for bacteria plated from stationary-phase culture than that from exponentially growing cells. This suggests that some specific processes, occurring predominantly in stationary-phase cells, facilitate generation and/or fixation of such mutations. </jats:p>