Molecular origin of transducing DNA in bacteriophage SPP1

Transducing particles produced by bacteriophage SPP1 infection of Bacillus subtilis were separated from plaque-forming units by CsCl density-gradient centrifugation. The density in CsCl of DNA isolated from such purified transducing particles was similar to that of bacterial DNA, indicating that the transducing particles probably contain DNA of exclusively bacterial origin. Bacterial DNA synthesized after infection of the donor culture was also encapsulated in the transducing particles. The number of transducing particles was at least 10 times higher than that of the transductants.