Phenotypic and Genetic Diversity of Benomyl-Degrading Bacteria Isolated from Agricultural Soils

Abstract

Benomyl is a benzimidazole family of fungicide which is used for fungi control in agricultural soils. Although benomyl has been used worldwide, a few benomyl-degrading microorganisms have been reported. In this study, nineteen bacterial strains were isolated from agricultural soils across Korea, and their phenotypic and genetic characteristics were investigated. The isolates were able to utilize benomyl as a sole carbon and energy source in mineral medium. Analysis of the 16S rRNA gene sequence revealed that all the isolates were related to members of the genera, Mycobacterium and Rhodococcus. Nine different chromosomal DNA fingerprinting patterns were obtained by polymerase-chain-reaction (PCR)amplification of repetitive extragenic palindromic (REP) sequences. The isolates were classified into three groups according to their growth and degradation properties, taking 48?100 hours to completely degrade 100ppm of benomyl in mineral medium. 2- aminobenzimidazole and 2-hydroxybenzimidazole were identified as intermediate metabolites by HPLC. Degradation experiments with various benzimidazoles showed that they had narrow degradation capabilities. They could degrade carbendazim but hardly utilized other benzimidazoles such as thiabendazole, thophanate-methyl, and fuberidazole. When analyzed with PCR amplification using previously reported carbendazim-hydrolyzing esterase gene, mheI, four isolates produced positive DNA bands. This is the first time that Mycobacterium can degrade benomyl as a sole carbon and energy source. Considering complete degradation capability of these strains, they might be useful for biodegradation in soils contaminated with benomyl.