Degradation of Ipconazole by Microorganisms Isolated from Paddy Soil

Abstract

Ipconazole is a triazole fungicide for treating rice seed. In the present study, degradation of ipconazole by isolated microorganisms from paddy soil was investigated. To enrich the degraders, the soil sample was perfused with ipconazole solution for 41 days. After the perfusion, the ipconazole-tolerant microbes in the perfused soil were cultivated on various media containing ipconazole. One bacterial, 12 actinomycetous, and 7 fungal strains showed ipconazole-degrading activity among 39 strains of bacteria, 14 strains of actinomycetes, and 14 strains of fungi in the liquid media containing 0.1 μg/ml ¹⁴C-ipconazole after 28 days of incubation. In particular, 8 strains of actinomycetes decomposed more than 90% of the ipconazole. The metabolism of ipconazole was investigated using two strains of actinomycetes, A1 and D16, with a higher level of degrading activity than the others. The isolates A1 and D16 were identified as Kitasatospora sp. and Streptomyces sp., respectively. A1 degraded more than 80% of the applied ipconazole after 3 days incubation in a liquid culture containing ¹⁴C-ipconazole at 1 μg/ml. D16 degraded approximately 20% of the applied ipconazole after 2 days, but more than 99% after 6 days of incubation. The primary metabolic reaction could be dominated by oxidation at either the carbon of the methine in the isopropyl group or the carbon of the benzylmethylene. A1 and D16 also possess the ability to oxidize the carbon of the methyl portion of the isopropyl group as well as that of the methylene portion of the cyclopentane ring. The polar metabolites in ethyl acetate extracts had increased by the end of incubation. 1,2,4-Triazole was detected as a water-soluble metabolite in the culture. There is little information available regarding microbial degradation of azole compounds, but our results suggest that some soil microorganisms contribute to the biodegradation of the triazole fungicide ipconazole in soil.