Diauxic growth was observed in anaerobic C(4)-dicarboxylate-adapted cells of "Aromatoleum aromaticum" EbN1 due to preferred benzoate utilization from a substrate mixture of a C(4)-dicarboxylate (succinate, fumarate, or malate) and benzoate. Differential protein profiles (two-dimensional difference gel electrophoresis [2D DIGE]) revealed dynamic changes in abundance for proteins involved in anaerobic benzoate catabolism and C(4)-dicarboxylate uptake. In the first active growth phase, benzoate utilization was paralleled by maximal abundance of proteins involved in anaerobic benzoate degradation (e.g., benzoyl-coenzyme A [CoA] reductase) and minimal abundance of DctP (EbA4158), the periplasmic binding protein of a predicted C(4)-dicarboxylate tripartite ATP-independent periplasmic (TRAP) transporter (DctPQM). The opposite was observed during subsequent succinate utilization in the second active growth phase. The increased dctP (respectively, dctPQM) transcript and DctP protein abundance following benzoate depletion suggests that repression of C(4)-dicarboxylate uptake seems to be a main determinant for the observed diauxie.