Temperate phages are bacterial viruses that either reside integrated in
a bacterial genome as lysogens or enter a lytic lifecycle. Decision
between lifestyles is determined by a switch involving a phage-encoded
repressor, CI, and a promoter region from which lytic and lysogenic
genes are divergently transcribed. Here we investigate the switch of
phage phi13 from the human pathogen Staphylococcus aureus. phi13 encodes
several virulence factors and is prevalent in S. aureus strains
colonizing humans. We show that the phi13 switch harbors a cI gene, a
predicted mor (modulator of repression) gene, and three high-affinity
operator sites binding CI. To quantify the decision between lytic and
lysogenic lifestyle, we introduced reporter plasmids that carry the 1.3
kb switch region from phi13 with the lytic promoter fused to lacZ into
S. aureus and B. subtilis. Analysis of beta-galactosidase expression
indicated that decision frequency is independent of host factors. The
white “lysogenic” phenotype, which relies on expression of cI, could
be switched to a stable blue “lytic” phenotype by DNA damaging agents.
We have characterized lifestyle decisions of phage phi13, and our
approach may be applied to other temperate phages encoding virulence
factors in S. aureus.
Characterization of the genetic switch from phage ɸ13 important for
Staphylococcus aureus
colonization in humans
