Catabolite repression of the toluene degradation pathway in Pseudomonas putida harboring pWW0 under various conditions of nutrient limitation in chemostat culture.

摘要

In earlier studies, the pathway of toluene and m- and p-xylene degradation (TOL pathway) in Pseudomonas putida (pWW0) was found to be subject to catabolite repression when the strain was grown at the maximal rate on glucose or succinate in the presence of an inducer. This report describes catabolite repression of the TOL pathway by succinate in chemostat cultures run at a low dilution rate (D = 0.05 h-1) under different conditions of inorganic-nutrient limitation. The activity of benzylalcohol dehydrogenase (BADH) in cell extracts was used as a measure of the expression of the TOL upper pathway. When cells were grown in the presence of 10 to 15 mM succinate under conditions of phosphate or sulfate limitation, the BADH activity in response to the nonmetabolizable inducer o-xylene was less than 2% of that of cells grown under conditions of succinate limitation. Less repression was found under conditions of ammonium or oxygen limitation (2 to 10% and 20 to 35%, respectively, of the BADH levels under succinate limitation). The BADH expression levels determined under the different growth conditions appeared to correlate well with the mRNA transcript levels from the upper pathway promoter (Pu), which indicates that repression was due to a blockage at the transcriptional level. The meta-cleavage pathway was found to be less susceptible to catabolite repression. The results obtained suggest that the occurrence of catabolite repression is related to a high-energy status of the cells rather than to a high growth rate or directly to the presence of growth-saturating concentrations of a primary carbon and energy source.