The catechol 1,2 dioxygenase system of Acinetobacter radioresistens: Isoenzymes, inductors and gene localisation

Two different isozymes (Iso A and Iso B) of catechol 1,2 dioxygenase (C1,2O ) were isolated from cultures of A. radioresistens grown in two different m edia, containing phenol and benzoate respectively. In the phenol medium the bacteria expressed about 90% of Iso A, whereas in the benzoate medium the Iso A/Iso B ratio was 40:60. The two proteins have different molecular mass es, isoelectric points and N-terminal sequences that are not consistent wit h simple posttranslational modifications. Furthermore, their behaviour diff ers at high temperatures (42 degreesC-47 degreesC) and at moderately acidic pH (pH 6.0): Iso A proved to be the more stable under conditions of enviro nmental stress. Hybridisation analysis with an A. calcoaceticus catA-derive d probe revealed that A. radioresistens C1,2O proteins are encoded by two c hromosomally located genes. Bidimensional electrophoresis (2DE) maps of cru de extracts of cells grown in different carbon sources (phenol, benzoate an d acetate) clearly demonstrated a differential induction pattern for the tw o proteins. The hypothesis of a double set of genes, one for benzoate catab olism and the other for phenol catabolism, is discussed, and analogies are drawn with other known C1,2Os.