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 ([http://www.ncbi.nlm.nih.gov/pubmed/11722885|Sorensen et al., 2001]). Isoproturon in soil is degraded, producing carbon dioxide and degradation products ([http://www.ncbi.nlm.nih.gov/pubmed/11482681|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 ([http://www.ncbi.nlm.nih.gov/pubmed/11482681|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 ([http://www.ncbi.nlm.nih.gov/pubmed/12089031|Sorensen et al., 2002]).