Defense Date


Document Type


Degree Name

Doctor of Philosophy


Microbiology & Immunology

First Advisor

Dr. Gail E. Christie


Staphylococcal pathogenicity island SaPI1 is excised from genomic DNA and extrachromosomal copies are amplified during the vegetative growth of staphylococcal phage 80α. The amplified genetic element is subsequently encapsidated and transduced at very high frequency. Previous studies have demonstrated that the transducing particles have virions with tails that appear identical to those of helper phage 80α but have smaller capsids, commensurate with the smaller genome of the SaPI (Lindsay, 1998). The morphology of the transducing particles, coupled with the observation that the genomic sequence of SaPIl (GenBank U93688) does not reveal any obvious phage structural proteins, has led to the hypothesis that SaPIl is encapsidated in a virion comprised of 80α structural proteins. Analysis of SaPIl transducing particles supports this hypothesis. Further investigation of 80α genes involved in SaPI1 mobilization was accomplished by selection of phage mutants resistant to SaPI1 interference. Two classes of SaPI1 jnterference resistant (sir) mutants were obtained, and point mutations were identified in two adjacent genes. In order to confirm the roles of these genes, an in-frame deletion of each candidate gene was constructed in an 80α prophage. All mutant phage and deletion constructs were evaluated for phage replication, SaPI1 replication, SaPIl transduction and SaPI1 interference. One gene (ORF21) was required for 80α growth and replication, but was not required for SaPIl growth or replication. The second gene (ORF22) was not essential for phage replication, but was required for SaPIl replication and high frequency transduction. The product of this gene was subsequently shown to be required for SaPIl excision.


© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

June 2008