In our previous study, the isoproturon-degrading strain Sphingomonas sp. Y57 was isolated from the wastewater treatment system of an herbicide factory. Interestingly, this strain also showed the ability to degrade propanil (3,4-dichloropropionamilide). The present work reveals that Y57 degrades propanil via the following pathway: propanil was initially hydrolyzed to 3,4-dichloroaniline (3,4-DCA) and then converted to 4,5-dichlorocatechol, which was then subjected to aromatic ring cleavage and further processing. N-acylation and N-deacylation of 3,4-DCA also occurred, and among N-acylation products, 3,4-dichloropropionanilide was found for the first time. The gene encoding the propanil hydrolase responsible for transforming propanil into 3,4-DCA was cloned from Y57 and was designated as prpH. PrpH was expressed in Escherichia coil BL21 and purified using Ni-nitrilotriacetic acid affinity chromatography. PrpH displayed the highest activity against propanil at 40 degrees C and at pH 7.0. The effect of metal ions on the propanil-degrading activity of PrpH was also determined. To our knowledge, this is the first report of a strain that can degrade both propanil and 3,4-DCA and the first identification of a gene encoding a propanil hydrolase in bacteria. (C) 2011 Elsevier B.V. All rights reserved.