The regulation of catabolic pathway of aromatic compound degradation in Acinetobacter radioresistens: physiological and molecular aspects.

The Acinetobacter radioresistens strain was isolated in our laboratories from an activated sludge pilot plant. It is able to grow in presence of either phenol or benzoate as the sole carbon and energy source, metabolizing them via the ortho pathway. A proteomic approach to the study of the regulation of these catabolic pathways showed that the expression of most of the catabolic enzymes is modulated by the growth substrate (1, 2). Moreover, “satellite” proteins were identified (porins, chaperonins), specifically induced by aromatics and probably involved in the uptake of these molecules and in the physiological cell response to their presence. In the present research these results have been extended by a more precise kinetic analysis of the bacterial growth on either an aromatic (phenol or benzoate) or a non-aromatic (acetate) carbon source. From these experiments it can be seen that cultures grown in presence of phenol or acetate show similar specific growth rates (=0.769 and 0.766 h-1 respectively) and yields (Y=11.1 and 11.6 g/Cmol), while benzoate supports less efficient growth (= 0.520 h-1, Y= 10,1 g/Cmol). Furthermore bacteria were grown in presence of substrate mixtures or utilizing cross-acclimatised cells. The study was finally completed by a transcriptome analysis of the most relevant catabolic genes (Phenol Hydroxylase, Benzoate Dioxygenase, Catechol 1,2-Dioxygenase). These results allow us to have a global picture of the complex regulation phenomena involved, both at mRNA, at proteins and at cellular level.