Understanding polylysogeny: Phage phiNP contributes to the fitness of its host, C. rodentium, in vitro

Citrobacter rodentium is a murine host adapted member of the attaching and effacing (A/E) family of pathogens, and is an important model in the study of the closely related diarrheal pathogens, Enteropathogenic Escherichia coli (EPEC) and Enterohaemorrhagic E. coli (EHEC). Much complexity of this model remains unknown, including the interaction between phages and the virulence of C.rodentium. Previous research has shown that C.rodentium DBS100 contains 10 prophages, while only two have been shown to be active temperate phages. While most intestinal bacteria are lysogens, the role of multiple phage carriage in host fitness and colonization is largely unstudied. Here we 1) examine the lifecycle of phiNP as a potential phagemid, 2) begin understanding the in vitro role of this phage during bacterial competition and 3) the impact of polylysogenic interactions on host colonization in vitro. We are studying the contribution of these phage to the competitiveness of their host, DBS100. We hypothesize a competitive advantage of the polylysogen compared to both the mono and nonlysogen counterparts in vitro, given the presence of virulence genes and interaction between phages. Polylysogeny, has been shown to mediate bacteria–bacteria competition, with this in mind we aim to understand how phages phiNP and Shae_phiSM contribute to the polylysogenic nature of DBS100. We show that phiNP enters a lysogenic lifecycle that is maintained during the hosts stationary phase, correlating with the drastic reduction in host fitness observed in the phiNP nonlysogen. Another interaction being studied is the recombination that occurs between Shae_phiSM a P2-like temperate phage and the a putative P4-like satellite, CRPr20, that is required for virion production. This P2-P4 interaction may be used as a model to understand one role of polylysogeny and the importance of phage interactions for the colonization of C.rodentium DBS100.