Role of phage ?1 in two strains of Salmonella Rissen, sensitive and resistant to phage ?1
The study describes the Salmonella Rissen phage ?1 isolated from the ?1-sensitive Salmonella Rissen strain RW. The same phage was then used to select the resistant strain R R?1+, which can harbour or not ?1. Following this approach, we found that ?1, upon excision from R W cells with mitomycin, behaves as a temperate phage: lyses host cells and generates phage particles; instead, upon spontaneous excision from RR?1+ cells, it does not generate phage particles; causes loss of phage resistance; switches the O-antigen from the smooth to the rough phenotype, and favors the transition of Salmonella Rissen from the planktonic to the biofilm growth. The RW and RR?1+ strains differ by 10 genes; of these, only two (phosphomannomutase_1 and phosphomannomutase_2; both involved in the mannose synthesis pathway) display significant differences at the expression levels. This result suggests that phage resistance is associated with these two genes. Phage ?1 displays the unusual property of behaving as template as well as lytic phage. This feature was used by the phage to modulate several phases of Salmonella Rissen lifestyle.