ISOLATION OF ISOPROTURON-DEGRADING BACTERIA FROM TREATED SOIL VIA 3 DIFFERENT ROUTES

Three different isolation routes (flask enrichment/flask degradation a ssay, flask enrichment/microplate degradation assay, MPN assay/micropl ate degradation assay) were used to obtain pure cultures of bacteria w hich degraded isoproturon (3-(4-isopropylphenyl-)-1,l-dimethylurea) as sole carbon and nitrogen source in a mineral salts medium from a fiel d soil treated with isoproturon in the laboratory. All three isolation routes were successful, but the microplate assay of degradation was m ore successful than the flask assay. Characterization of 36 isolates i ndicated that they formed 16 distinct phenotypes (10 Grampositive phen otypes, six Gram-negative phenotypes) which are likely to represent di stinct species. Low concentrations of the degradation product 3-(4-iso propylphenyl)-1-methylurea (IPPMU) were occasionally found in the cult ure solutions. When provided as the sole source of carbon and nitrogen , the monomethyl degradation product was itself rapidly degraded by se veral of the isolates. Some isolates were also able to use the demethy lated degradation product 3-(1-isopropylphenyl)-urea (IPPU) as sole so urce of carbon and nitrogen, although there was occasionally an extend ed lag-phase before rapid degradation commenced. One isolate was parti cularly active and degraded isoproturon, the monomethyl and demethylat ed degradation products of isoproturon, and demethylated the related p henylureas diuron and linuron.