Physiological analysis of the expression of the styrene degradation gene cluster in Pseudomonas fluorescens ST

The effects of different carbon sources on expression of the styrene catabo lism genes in Pseudomonas fluorescens ST were analyzed by using a promoter probe vector, pPR9TT, which contains transcription terminators upstream and downstream of the beta-galactosidase reporter system. Expression of the pr omoter of the stySR operon, which codes for the styrene two-component regul atory system, was found to be constitutive and not subject to catabolite re pression. This was confirmed by the results of an analysis of the stySR tra nscript in P. fluorescens ST cells grown on different carbon sources. The p romoter of the operon of the upper pathway, designated PstyA, was induced b y styrene and repressed to different extents by organic acids or carbohydra tes. In particular, cells grown on succinate or lactate in the presence of serene started to exhibit beta-galactosidase activity during the mid-expone ntial growth phase, before the preferred carbon sources were depleted, indi cating that there is a threshold succinate and lactate concentration which allows induction of styrene catabolic genes. In contrast, cells grown on gl ucose, acetate, or glutamate and styrene exhibited a diauxic growth curve, and beta-galactosidase activity was detected only after the end of the expo nential growth phase. In each experiment the reliability of the reporter sy stem constructed was verified by comparing the beta-galactosidase activity and the activity of the styrene monooxygenase encoded by the first gene of the styrene catabolic operon.