Rapid Isolation of DNA from Staphylococcus aureust

Purification of bulk DNA is basic to many of the molecular biological techniques currently in use. Isolation procedures are generally based on some variation of the method of Kirby (1) or Marmur (5) and involve the use of enzymes, detergents, and phenol to digest, denature, and extract many of the macromolecular components which contaminate the DNA. These extractions are often followed by centrifugation of the DNA to equilibrium in CsCl or CsCI-ethidium bromide buoyant density gradients (8) as a final step in purification. In our experience, difficulties in obtaining biochemically useful material are often encountered with DNA isolated from many strains of Staphylococcus aureus. There are S. aureus DNA purification protocols which lead to preparations that are biologically active in transformation experiments (2, 10; M. R. Gilmore, personal communication). However, the DNA often has little utility in a biochemical sense (susceptibility to the action of DNA-modifying enzymes). For instance, the DNA from one strain of S. aureus may be amenable to restriction enzyme cleavage, whereas the DNA from a second strain is not; often, DNA samples purified from the same S. aureus strain at different times will vary in restriction enzyme susceptibility. This refractory behavior is caused by contaminants which are copurified with S. aureus DNA, but such contaminants have not yet been identified. In addition to these difficulties, procedures for isolating biochemically useful DNA samples are expensive and time consuming, often involving prolonged digestion with proteolytic enzymes and repeated rounds of CsCl centrifugation. Consequently, we have searched for an alternative purification scheme that is less laborious and expensive and leads to purified S. aureus DNA that is useful biochemically as well as