Benzoate degradation via the ortho pathway in Alcaligenes eutrophus is perturbed by succinate

During batch growth of Alcaligenes eutrophus on benzoate-plus-succinate mixtures, substrates were simultaneously metabolized, leading to a higher specific growth rate (mu = 0.56 h(-1)) than when a single substrate was used (mu = 0.51 h(-1) for benzoate alone and 0.44 h(-1) for succinate alone), without adversely affecting the growth yield (0.57 Cmol/Cmol), Flux distribution analysis revealed that succinate dehydrogenase most probably controls the rate of total succinate consumption (the maximum flux being 9.7 mmol.g(-1).h(-1)). It is postulated that the relative consumption rate of each substrate is in part related to modified levels of gene expression but to a large extent is dependent upon the presence of succinate, end product of the beta-ketoadipate pathway, Indeed, the in vitro beta-ketoadipate-succinyl coenzyme A transferase activity was seen to be inhibited by succinate, a coproduct of the reaction.