The Salmonella enterica subspecies I specific centisome 7 genomic island encodes novel protein families present in bacteria living in close contact with eukaryotic cells

We have determined the genetic structure of the Salmonella enterica centisome 7 genomic island (SCI) located at the aspV loci in S. enterica subspecies I strains. The 47-kb long genomic island encodes 37 putative proteins, including the previously described saf fimbrial operon and the sinR transcriptional regulator. Other open reading frames (designated sci A to Z) in the island encode putative proteins with homologies to virulence-associated proteins in a number of Gram-negative bacteria such as Pseudomonas aeruginosa, Yersinia pestis and enterohemorrhagic Escherichia coli, bacteria that have the ability to interact with and manipulate eukaryotic cells. The Sci proteins have putative cytoplasmic, periplasmic and outer membrane localizations pointing to a role in extracellular processes such as secretion or organelle biosynthesis. The genes encoding Sci-like proteins are clustered in all sequenced bacterial genomes available in the databases and a core set can be defined by the presence of genes encoding proteins with similarity to the SciB, C, G, H, I, O proteins. The SCI genomic island DNA sequences are restricted to Salmonella strains belonging to S. enterica subspecies I and deletion of the entire island affects the ability of the organisms to enter eukaryotic cells.