DIVERSITY OF CARBOFURAN-DEGRADING SOIL BACTERIA AND DETECTION OF PLASMID-ENCODED SEQUENCES HOMOLOGOUS TO THE MCD-GENE

Fifty-five bacterial isolates, from English and French soils with diff erent histories of carbofuran field treatment, which hydrolysed the N- methylcarbamate insecticide carbofuran to carbofuran 7-phenol were cha racterised phenotypically and genetically. The isolates were compared by using 125 physiological tests and morphological features, plasmid p rofiles and restriction fragment length polymorphism (RFLP) patterns o f total DNA using the rRNA operon of Escherichia coil as a DNA probe. Cluster analysis of both phenotypic characters and RFLP patterns showe d a high degree of diversity amongst the bacteria. Ten distinct plasmi d profiles with 2-4 plasmids ranging in size from 84 to about 438 kb w ere visualised in 50 isolates. The majority of isolates had one of two types of plasmid profiles. Plasmid profiles and EcoRI restricted tota l DNA patterns were hybridised with an internal fragment of the carbof uran hydrolase (mcd) gene and 22 diverse soil isolates exhibited seque nce homology with this gene probe. Our results indicate that sequences homologous to the mcd gene are located on a conserved EcoRI fragment (12 or 14 kb) of a plasmid (100, 105, 115 or 124 kb) found in diverse soil isolates from geographically distant areas. Thirty-three isolates did not exhibit detectable homology to the mcd gene probe and the hyd rolase enzymes and genes in these isolates need further investigation.