Isolation of a temperate bacteriophage encoding the type III effector protein SopE from an epidemic Salmonella typhimurium strain

摘要

Salmonella typhimurium employs the special- ised type III secretion system encoded in pathogenicity island 1 (SPI1) to translocate effector proteins into host cells and to modulate host cell signal transduction. The SPI1 type III system and the effector proteins are conserved among all salmonellae and are thought to be acquired by horizontal gene transfer. The genetic mechanisms mediating this horizontal transfer are un- known. Here, we describe that SopE, a SPI1-dependent translo- cated effector protein, is present in relatively few S. typhimurium isolates. We have isolated a temperate phage that encodes SopE. Phage morphology and DNA hybridization, as well as partial sequence information, suggest that this phage (SopE#PHI#) is a new member of the P2 family of bacteriophages. By lysogenic con- version this phage can horizontally transfer genes between different S. typhimurium strains. Strikingly, most of the isolates harboring SopE#PHI# belong to the small group of epidemic strains of S. typhimurium that have been responstble for a large per- centage of human and animal salmonellosis and have persisted for a long period of time. Our data suggest that horizontal transfer of type III dependent effector proteins by lysogenic infection with bacteriophages (lysogenic conversion) may pro- vide an efficient mechanism for fine-tuning the interaction of Salmonella spp. with their hosts.