A C7 dicarboxylic (pimelic) acid derivative is postulated as an intermediate in anaerobic degradation of benzoate. Four strains of Gram-negative, nitrate-reducing bacteria capable of growth with both pimelate and benzoate as sole carbon and energy source were isolated. The metabolism of strain LP-1, which was enriched from activated sludge with pimelate as substrate, was studied in detail. This strain grew only with oxygen or with oxidized nitrogen compounds as electron acceptor. In the presence of nitrate, a wide range of substrates excluding C1 compounds was degraded. The new isolate was catalase- and oxidase-positive, and had one single polar flagellum. Strain LP-1 was tentatively classified within the family Pseudomonadaceae. The catabolism of pimelate and benzoate was studied in cell-free extracts of strain LP-1. Both acids were activated with coenzyme A in a Mg(2E)- and ATP-dependent reaction. The corresponding acyl-CoA synthetases were specifically induced by the respective growth substrate. Pimelate was also activated by CoA transfer from succinyl-CoA. Pimelyl-CoA was oxidized by cell-free extracts in the presence of potassium ferricyanide. Degradation to glutaryl-CoA and acetyl-CoA proceeded by a sequence of beta-oxidation-like reactions. Glutaryl-CoA dehydrogenase and glutaconyl-CoA decarboxylase activities were expressed in cells grown with pimelate or benzoate, indicating the specific involvement of these enzyme activities in anaerobic degradation of these two acids. Enzyme activities responsible for further degradation of the resulting crotonyl-CoA to acetyl-CoA via classical beta-oxidation were also detected.