Acinetobacter lwoffii K24 is a known aniline-degrading bacterium. In previous studies, two catechol branches of the beta-ketoadipate pathway were reported to be induced for aniline degradation, and related enzymes (CatA(1) and CatA(2)) were identified from the aniline-induced proteome of A. lwoffii K24 [S.I. Kim, S.H. Leem, J.S. Choi, Y.H. Chung, S. Kim, Y.M. Park, Y.K. Park, Y.N. Lee, K.S. Ha, Cloning and characterization of two catA genes in Acinetobacter lwoffii K24, J. Bacteriol. 179 (1997) 5226-5231; and E.A. Kim, J.Y. Kim, S.J. Kim, K.R. Park, H.J. Chung, S.H. Leem, S.I. Kim, Proteomic analysis of Acinetobacter lwoffii K24 by 2-D gel electrophoresis and electrospray ionization quadrupole-time of flight mass spectrometry, J. Microbiol. Methods 57 (2004) 337-349]. A. lwoffii K24 has also been found to utilize other aromatic compounds such as p-hydroxybenzoate, salicylate, and benzoate. In this study, we performed a comparative 2-DE/MS analysis of a benzoate-induced proteome and found that a new catechol 1,2-dioxygenase (CatA(3)) and benzoate 1,2-dioxygenase were up-regulated as the primary dioxygenases responsible for benzoate degradation in A. lwoffii K24. However, CatA(1) and CatA(2) were not detected on the same 2D gel as CatA(3). Transcription analysis of three catA genes from A. lwoffii K24 showed that these cat genes were specifically expressed under certain growth conditions using different aromatic compounds as the carbon source. While catA(1) and catA(2) were expressed under the aniline culture condition, catA(3) was expressed under the benzoate culture condition. A new cat gene cluster (catB(3)C(3)A(3)F(3)) was cloned and found to share sequence homology and a similar gene structure with the cat genes of Acinetobacter radioresistens. This result suggests that the third catechol branch (cat(3)) of the beta-ketoadipate pathway was selectively induced for the degradation of benzoate in A. lwoffii K24. It also provides evidence of multiple catechol branches in the beta-ketoadipate pathway and the independent regulation of monocyclic aromatic compound degradation in A. lwoffii K24.