Isolation and characterization of fenobucarb-degrading bacteria from rice paddy soils

Forty-five fenobucarb-degrading bacteria were isolated from rice paddy soils, and their genetic and phenotypic characteristics were investigated. The isolates were able to utilize fenobucarb as a sole source of carbon and energy. Analysis of the 16S rRNA gene sequence indicated that all the isolates were related to members of the genera Sphingobium and Novosphingobium. Among 45 isolates, 21 different chromosomal DNA fingerprinting patterns were obtained. All these strains exhibited similar growth and degradation patterns on fenobucarb. 2-sec-butylphenol was identified as an intermediate during fenobucarb degradation by HPLC analysis. All of the isolates were able to degrade another carbamate insecticide, carbaryl, and 2-sec-butylphenol, but not other fenobucarb related compounds such as aldicarb and fenoxycarb. Representative strains of the different repetitive extragenic palindromic sequence PCR fingerprint types had one to six plasmids. The plasmid-cured strains lost their degradation abilities, suggesting that fenobucarb degradative genes were on their plasmid DNAs in these strains. When analyzed with PCR amplification using the primers targeting for the previously reported carbamate hydrolase genes, most of the isolates did not exhibit any positive signals for different genes involved in carbamate degradation such as mcd, cahA and cehA genes. This is the first report that microorganisms involved in the degradation of fenobucarb have been isolated and the intermediate of fenobucarb biodegradation was identified.