Isolation from agricultural soil and characterization of a Sphingomonas spable to mineralize the phenylurea herbicide isoproturon

A soil bacterium (designated strain SRS2) able to metabolize the phenylurea herbicide isoproturon, 3-(4-isopropylphenyl)-1,1-dimethylurea (IPU), was i solated from a previously IPU-treated agricultural soil. Based on a partial analysis of the 16S rRNA gene and the cellular fatty acids, the strain was identified as a Sphingomonas sp. within the alpha -subdivision of the prot eobacteria. Strain SRS2 was able to mineralize IPU when provided as a sourc e of carbon, nitrogen, and energy. Supplementing the medium with a mixture of amino acids considerably enhanced IPU mineralization. Mineralization of IPU was accompanied by transient accumulation of the metabolites 3-(4-isopr opylphenyl)-1-methylurea, 3-(4-isopropylphenyl)-urea, and 4-isopropyl-anili ne identified by high-performance liquid chromatography analysis, thus indi cating a metabolic pathway initiated by two successive N-demethylations, fo llowed by cleavage of the urea side chain and finally by mineralization of the phenyl structure. Strain SRS2 also transformed the dimethylurea-substit uted herbicides diuron and chlorotoluron, giving rise to as-yet-unidentifie d products. In addition, no degradation of the methoxy-methylurea-substitut ed herbicide linuron was observed. This report is the first characterizatio n of a pure bacterial culture able to mineralize IPU.