Why can transfer of DNA by conjugation cross genus lines, whereas transfer of DNA by natural transformation or phage transduction is usually limited to a few closely related organisms? Some integrons...

Why can transfer of DNA by conjugation cross genus lines, whereas transfer of DNA by natural transformation or phage transduction is usually limited to a few closely related organisms?

Some integrons that contain disinfectant resistance genes or mercury resistance genes, as well as antibiotic resistance genes, have been found. What is the potential significance of this association?