Investigation of horizontal gene transfer potential from Bt176 maize to phytopathogenic bacterium Erwinia stewartii 1082

To analyse the frequency of natural gene transfer from genetically modified maize to phytopathogenic bacterium Erwinia stewartii 1082, a marker rescue system based on the restoration of ampicillin resistance gene was used in in vitro and in planta transformation experiments. A set of three vectors containing defined deletions of the blaTEM116 ampicillin resistance gene in pBR322 was constructed. Recombinant strains of Erw. stewartii 1082 harboring these mutant plasmids were used for infection of transgenic maize plants. Restoration of ampicillin resistance was observed only in transformed electro-competent Erw. stewartii 1082 cells. Frequency of the resistance restoration was found to be dependent on the size of the transforming DNA. In addition, highly active non-specific endodeoxyribonuclease was detected in cell-free lysates of Erw. stewartii 1082, rapidly degrading linear DNA fragments. No ampicillin resistant Erw. stewartii 1082 transformants were observed during in planta experiments indicating that this pathogenic bacterium is not naturally transformable under the conditions tested in this study.