Bacteriophages represent one group of mobile genetic elements with great impact on bacterial pathogenicity. In addition to taking part in the regulation of microbial diversity and ecology, bacteriophages themselves encode toxins and virulence factors affecting bacterial pathogenicity. Besides their own transfer, they can also mobilise host genomic segments and other mobile genetic elements such as pathogenicity islands and the virulence factors that they encode (Penadés et al., 2015). Although it has been classically assumed that generalised transduction only involves pac phages, it has been recently proposed that cos phages are also involved in the intra-generic and inter-generic transfer of pathogenicity islands, broadening the impact of these type of bacteriophages in the transfer of virulence genes among bacteria (Quiles-Puchalt et al., 2014; Chen et al., 2015). According to this newly acquired relevance in the horizontal gene transfer process and in an attempt to further characterise their biology, we have studied the Staphylococcus aureus bacteriophage 12 as a model for these cos bacteriophages.
In this study we have focused in the characterisation of the replication module of the S. aureus bacteriophage 12. An in silico analysis showed that it encodes for five putative replication genes. To study the role of these genes, individual mutants have been obtained and then tested for the viability and replication process of the bacteriophage and their role in the transfer of staphylococcal pathogenicity islands (SaPIs). Our results suggest that two of these proteins are essential for the phage viability and transfer of SaPI. Two other mutants show sharply reduction in phage and SaPI transfer, while the last one has no significant effect for the phage. These in vivo results along with other in vitro techniques would allow us to decipher the replication mechanism of the S. aureus bacteriophage 12 and how it is involved in virulence transfer.