The Acinetobacter baylyi strain GFJ2 was isolated from soil that was potentially contaminated with herbicides. It exhibited complete biodegradations of 4-chlroaniline (4CA) and 3,4-dichloroaniline (34DCA), a wide range of monohalogenated anilines (chloro-, bromo-, and fluoro-anilines) and other dichloroanilines. An in-depth investigation of the biodegradation pathway revealed that a dechlorination reaction may be involved in 34DCA biodegradation, which forms 4CA as the first intermediate. By detecting the transient intermediates and characterizing the relevant enzymes, this investigation is also the first to report that A. baylyi strain GFJ2 has two distinct 4CA degradation pathways that yield 4-chlorocatechol (4CC) and aniline as the first intermediate in each route, which are further metabolized through an ortho-cleavage pathway. Analysis of biodegradation kinetics analysis illustrated that A. baylyi GFJ2 utilized aniline and 4CC at significantly slower rates than it used 4CA, suggesting that the transformations of aniline and 4CC were probably the limiting steps during 4CA biodegradation. Our results suggest the potential application of A. baylyi strain GFJ2 in bioremediation and waste treatment, and the kinetic data provide the insights into the degradation mechanism, dynamics and possible limitations of the biodegradation which include substrate and product inhibitions. (C) 2010 Elsevier B.V. All rights reserved.