Selective deletions involving the organophosphorus hydrolase gene adpB from Nocardia strain B-1

The organophosphorus hydrolase (OPH) of Nocardia sp. strain B-1 is capable of hydrolyzing organophosphate insecticides such as coumaphos and parathion. The 40,000 dalton OPH and the responsible gene (termed adpB) have been previously isolated and described. OPH activity in Nocardia strain B-1 is spontaneously lost at high frequency during the growth of laboratory cultures. In order to understand the genetic basis of this phenomenon, hybridization experiments were performed in which digested genomic DNAs from OPH negative derivatives were probed with BstE1 and BamH1 restriction fragments containing adpB and regions flanking this gene. These experiments revealed that a region containing adpB was missing in all OPH negative derivatives. However, these OPH negative derivatives were shown to contain sequences that hybridized to probes for DNA regions flanking adpB. On the basis of the hybridization patterns from thirteen OPH negative derivatives, there are two primary types of deletions with their sizes ranging from 33 kb to greater than 35.5 kb.