Soil properties affecting adsorption of plasmid DNA and its transformation efficiency in Escherichia coli

We examined the soil properties affecting adsorption of plasmid DNA and its transformation efficiency using competent Escherichia coli cells in sterile forested Andosols (n = 2), arable Andosols (n = 3), arable Cambisols (n = 2), and humic acid. Organic matter-removed soil samples were also prepared by subjecting each soil to ignition treatment. The amount of plasmid DNA adsorbed was influenced by individual soil properties rather than soil types and fertilizer management practices. Among the soil properties determined, organic matter content and pH appeared to have the greatest influence on the amount of DNA adsorbed onto soil samples. Adsorption of plasmid DNA greatly repressed the transformation efficiency of E. coli relative to free DNA. Decreased transformation efficiency was observed in samples showing high binding affinity for plasmid DNA, and the affinity appeared to be affected by exchangeable Ca, soil texture, and humic acid.