Identification of a Salmonella virulence gene required for formation of filamentous structures containing lysosomal membrane glycoproteins within epithelial cells

Abstract

Salmonella species are facultative intracellular pathogens that invade epithelial cells and reside within lysosomal membrane glycoprotein (Igp)-containing vacuoles. Coincident with the onset of bacterial replication inside these vacuoles, Salmonella induce the formation of stable Igp-containing filamentous structures that connect with the Salmonella-containing vacuoles. Salmonella typhimurium SL1344::Tn 10dCm mutant strains unable to induce these structures were isolated. All contained insertions within a novel Salmonella induced filament gene A (sifA). sifA is present only in Salmonella species and encodes a protein with a predicted molecular mass of 38kDa and an apparent molecular mass of 35kDa. sifA is flanked by ∼300 base pairs, and sifA and its flanking DNA show no homology to sequences in DNA databases. sifA is located within the potABCD operon, a housekeeping locus involved in periplasmic transport of polyamines. Fourteen-base-pair direct repeats mark the probable site of integration of sifA and its flanking DNA at the 3 end of potB. sifA and its flanking DNA have a significantly reduced G+C content (41%) when compared with the potABCD operon (51%) and the Salmonella genome (52–54%). Deletion mutant strains