Molecular cross-talk between Sa3int phages and their Staphylococcus aureus host

As a major opportunistic pathogen of human and animals Staphylococcus aureus asymptomatically colonizes the nasal cavity, but is also a leading cause of life-threatening acute and chronic infections. More than 90% of the human nasal isolates of S. aureus were found to carry Sa3int phages, which integrate as prophages into the bacterial hlb gene disrupting the expression of an important virulence factor. The virulence factor-encoding genes carried by the Sa3-phages are all highly human-specific and probably essential for bacterial survival in the human host. However, how the S. aureus host modulates the life cycle of those temperate phages remains largely unknown (1). Our data suggest that this regulation is strain specific, with certain S. aureus strains being more prone than others to support either a lysogenic or a lytic life cycle (2). We constructed S. aureus single lysogens with integrated Sa3int prophages and found significant differences in phage transfer rates between different strains. Based on this finding, strains were grouped into low and high transfer strains. To get a more precise picture of the regulatory circuits we constructed replication deficient mutants, performed differential RNAseq and analysed a set of mutant strains. Comparison of different mutants in phenotypic assays revealed roles of known global regulators of S. aureus, in phage infection and replication regulation. By transcriptional start site prediction we identified promoter-regions that are differentially active in high and low transfer strains and identified putative transcriptional regulators on phage and host site by pull down assays. Overall, our results suggest a more prominent role of the host background regulatory processes in different growth phases and strains than previously assumed.

1. Rohmer C, Wolz C. The Role of hlb-Converting Bacteriophages in Staphylococcus aureus Host Adaption. Microb Physiol. 2021;31(2):109-122. doi:10.1159/000516645

2. Rohmer C, Dobritz R, Tuncbilek-Dere D, et al. Influence of Staphylococcus aureus Strain Background on Sa3int Phage Life Cycle Switches. Viruses. 2022;14(11):2471. Published 2022 Nov 8. doi:10.3390/v14112471