Isoproturon Degradation Pathway

The phenylurea herbicide isoproturon (IPU) is used against annual grasses and broad-leaved weeds in cereal production across Europe, resulting in both surface water and ground water pollution (Sorensen et al., 2001). Isoproturon in soil is degraded, producing carbon dioxide and degradation products (Perrin-Gainer et al., 2001). The major biodegradation pathway of isoproturon is isoproturon -> mono-demethyl-isoproturon -> hydroxy-monodemethyl-isoproturon -> 4'-(2-hydroxyisopropylphenyl)urea -> 4'-(2-hydroxyisopropylphenyl)aniline. Other minor pathways exist. Through one of these, 4,4'-diisopropylazobenzene can accumulate in soil (Perrin-Ganier et al., 2001).

Attempts to isolate microorganisms which metabolize isoproturon have often failed. Recently, Sphingomnas sp. strain SRS2 was found to mineralize isoproturon. Sphingomnas sp. strain SRS2 is auxotrophic; it requires strain SRS1 to supply amino acids needed for the pathway (Sorensen et al., 2002).

The following is a text-format isoproturon degradation pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (9k) format.

                                      Isoproturon
                               Sphingomnas sp. strain SRS2
                                           |
                                           | isoproturon
                                           | dimethylamine-
                                           | dehydrogenase
                                           |
                                           v
                                Monodemethylisoproturon
                                           |
                                           |
                                           |
                          +----------------+-----------------+
                          |                                  |
            monodemethyl- |                    monodemethyl- |
              isoproturon |                      isoproturon |
           dimethylamine- |                    dehydrogenase |
            dehydrogenase |                                  |
                          |                                  |
                          |                                  |
                          v                                  v
                Didemethylisoproturon          Hydroxymonodemethylisoproturon
                          |  |                               |
              didemethyl- |  |                  hydroxymono- |
              isoproturon |  |                       methyl- |
                   amido- |  |                   isoproturon |
                hydrolase |  |                dimethylamine- |
                          |  |                 dehydrogenase |
                          |  |                               |
                          |  +-----------------------+       |
                          |                          |       |
                          |              didemethyl- |       |
                          |              isoproturon |       |
                          |            dehydrogenase |       |
                          |                          |       |
                          v                          v       v
                 4-Isopropylaniline          4'-(2-Hydroxyisopropyl)phenylurea
                          |  |                               |
                          |  |                4'-(2-hydroxy- |
                          |  |             isopropyl)phenyl- |
                          |  |                   urea amido- |
                          |  |                     hydrolase |
                        A |  |                               |
                          |  |                               |
                          |  +-----------------------+       |
                          |                          |       |
                          |              4-isoproyl- |       |
                          |                  aniline |       |
                          |            dehydrogenase |       |
                          |                          |       |
                          v                          v       v
             4,4'-Diisopropylazobenzene        4'-(2-Hydroxyisopropyl)phenylaniline
                                                             |
                                                             |
                                                             | B
                                                             v
                                                             |
                                                             |
                                                             v
                                                      Carbon dioxide

Isoproturon Pathway Map