Role of phage ϕ1 in two strains of Salmonella Rissen, sensitive and resistant to phage ϕ1

BACKGROUND: The study describes the Salmonella Rissen phage ϕ1 isolated from the ϕ1-sensitive Salmonella Rissen strain R(W). The same phage was then used to select the resistant strain R(R)ϕ1+, which can harbour or not ϕ1. RESULTS: Following this approach, we found that ϕ1, 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 R(R)ϕ1+ 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 R(W) and R(R)ϕ1+ 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. CONCLUSIONS: Phage ϕ1 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. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12866-018-1360-z) contains supplementary material, which is available to authorized users.