The Salmonella enterica Serovar Typhimurium Translocated Effectors SseJ and SifB Are Targeted to the Salmonella -Containing Vacuole

Abstract

ABSTRACT The Salmonella enterica serovar Typhimurium type III secretion system (TTSS) encoded in Salmonella pathogenicity island 2 (SPI-2) promotes replication within host cells and systemic infection of mice. The SPI-2 TTSS is expressed following Salmonella internalization into host cells and translocates effectors across the membrane of the Salmonella -containing vacuole (SCV). Two effectors with similar amino-terminal domains, SseJ and SifB, localize to the SCV membrane in infected HEp-2 cells and subsequently traffic away from the SCV along Salmonella- induced-filaments (Sifs). Following infection of RAW cells, SseJ and SifB localize to the SCV as well as LAMP-1-positive, vesicular-appearing structures distant from the SCV. Trafficking of SseJ and SifB away from the SCV requires the SPI-2 effector SifA. Deletion of sseJ , but not sifB , leads to attenuation of Salmonella replication in mice following intraperitoneal inoculation. The contribution of SseJ to in vivo replication is identical in wild-type and sifA deletion backgrounds, suggesting that SseJ trafficking away from the SCV along Sifs is unnecessary for its virulence function.