While studying a set of multiply marked mutants of Staphylococcus aureus strain 8325 by transformation, several instances of apparent genetic linkage were encountered. After showing that these linked transformations were readily inactivated by shearing of the deoxyribonucleic acid (DNA) but were resistant to dilution of the DNA, and showing that mixtures of DNA failed to form double transformants, it was concluded that the linkages were legitimate rather than the result of congression. Three linkage groups were defined: thy-101-lys-115-trp-103-thr-106, pyr-141-hisGb15-nov-pur-102, and pur-110-ilv-129. The positions of the previously studied trp and his operons corresponded to the trp-103 and hisGbl5 loci. The ilv-129 position adjacent to pur-l10 probably corresponds to the ilv-leu gene cluster. The distance over which linkage was detected was greater by transformation than by generalized transduction. 201 on August 11, 2020 by guest http://jb.asm.org/ Downloaded from for 30 min on a Burrell wrist-action shaker (Burrell distilled (under N2) phenol saturated with 0.01 Corp., Pittsburgh, Pa.). The lysis mixtures were then M Tris(hydroxymethylfaminomethane-hydrochloride extracted three times with equal volumes of freshly buffer, pH 8.

A 5.2-kilobase pair transposon, Tn551, has been found in Staphylococcus aureus, a Gram-positive bacterium. Initially detected on plasmid pI258, it undergoes rec-independent transposition to multiple chromosomal and plasmid sites, sometimes causing insertional inactivation. Unlike most other transposons, Tn551 undergoes apparently precise excision as a rule. The initial observation of Tn551 transition involved UV inactivation of the carrier plasmid; this would appear to be a general means of detecting transposable elements.

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Transformation provided definitive evidence for linkage between tyrB282::TnSSl ermB321 and fQ(Chr::TnS51)34, and thus between the separate large linkage groups containing these markers, in Staphylococcus aureus NCTC 8325. Transformation also defined the chromosomal loci for the purCJ93::TnSSJ and fQ(Chr::TnS51)42 markers and the linkage of a tetracycline resistance marker (tet-3490) with a fusidic acid resistance marker (fus-149). The use of DNA isolated from protoplasts under conditions that reduced hydrodynamic shear greatly facilitated the demonstration of most of these linkages. These results provide direct evidence confirming several of the linkages predicted by a microcomputerassisted protoplast fusion analysis in a previous study (M. L. Stahl and P. A. Pattee, J. Bacteriol. 154:395-405, 1983); those markers whose predicted linkages were not confirmed by transformation are probably separated by chromosomal distances that exceed the limits of detection by transformation, even with protoplast DNA.

When used in a helper phage capacity, phages 29, 52, 52A, 79, 80, 55, 71, 53, 83A, 85, 95, 96, 011, and 80a, all serological group B Staphylococcus phages, conferred competence for transformation to S. aureus 8325-4, a strain that does not normally become competent. Of the serological group A phages tested, only phage 3A showed significant competence-conferring activity. Phages 29, 55, 53, 83A, .85, 95, 411, and 80a showed an enhancement of competence-conferring activity if exposure to the cells occurred in the presence of normal rabbit serum. All of the propagating strains for the Staphylococcus reference typing phages were rendered competent for transformation by exposure to at least one of these helper phages. The use of a helper phage to confer competence to S. aureus did not result in distortion of the genetic linkages observed in an inherently competent strain. Lysogenization by phages 441 or 83A is shown not to be required for the expression of competence, and evidence is presented which indicates that competence in the inherently competent 8325 strain is due to a helper phage effect initiated by the adsorption to cells of 441 virion parts [or 411 particles in the case of the single lysogen 8325-4(41l)] that have been liberated by prophage induction.