The bacteriolytic activity in transgenic potatoes expressing a chimeric T4 lysozyme gene and the effect of T4 lysozyme on soil- and phytopathogenic bacteria

Recently potato plants expressing a chimeric gene for T4 lysozyme have been constructed with the aim to achieve resistance of potatoes against phytopathogenic bacteria during cultivation and storage, particularly against Erwinia carotovora causing black leg and soft rot. Here we show that in cell free extracts of tubers from the transgenic potato lines significantly higher lytic activity for bacteria is present than in the control lines. Further, the release of T4 lysozyme from roots of transgenic potatoes during growth in a nutrient solution was demonstrated by Western blots of the growth medium. In addition, it was observed that purified T4 lysozyme added to aqueous extracts of various soils maintained much of its bacteriolytic ic activity. The sensitivity of various soil bacteria against T4 lysozyme was determined by a survival assay. It was found that six strains of E. carotovora (subspecies carotovora and atroseptica) were similarly sensitive as the type strain employed in a previous sensitivity study. Among other soil bacteria examined for T4 lysozyme sensitivity, most of the Gram-negative (8 of 10) and all of the Gram-positive strains (4) turned out to be sensitive in the absence of a chelating agent for divalent cations. The results are discussed with respect to possible effects associated with the growth of lysozyme-producing plants on the soil microbiota.