Transfection of Staphylococcus aureus with bacteriophage deoxyribonucleic acid

Staphylococcus aureus cells of strain 8325 (N) are competent for phage deoxyribonucleic acid (DNA) when harvested in the early exponential growth phase. Phenotypic expression of the competence requires divalent cations, and calcium ions are most effective. Treatment of phage DNA with deoxyribonuclease completely destroys infectivity and heat-denaturated DNA is not infectious. The highest frequency of transfection is around 10(4) plaque-forming units per mug of DNA.