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Repression of enzymes contributing to degradation of aromatic compounds via the b-ketoadipate pathway in the presence of additional carbon sources (carbon catabolite repression) in the bacterium Acinetobacter sp. strain ADP1 is described. The phenomenon was investigated on the level of specific activity of protocatechuate 3, 4-dioxygenase and p-hydroxybenzoate hydroxylase participating in catabolism of protocatechuate and p-hydroxybenzoate. Strong repression (90%) was found in cells grown on succinate and acetate in addition to the aromatic carbon source; partial derepression occurred towards the end of the logarithmic growth phase. Glucose, pyruvate, or lactate as secondary carbon sources had no repressing effect. The consumption of the aromatic substrate from the medium was delayed in the presence of acetate and succinate. The differences in specific enzyme activities were reflected at the transcript level for three operons connected to catabolism of aromatic compounds (pob, pca, van) as shown by Northern blot hybridization. Transcriptional fusions between the promoters of the pob and the pca operon identified the transcriptional level as the regulatory one. A mechanism of global regulation is postulated, which enables the organism to consume the offered carbon sources hierarchically in the most efficient manner.