IDENTIFICATION AND SEQUENCE-ANALYSIS OF A 27-KILOBASE CHROMOSOMAL FRAGMENT CONTAINING A SALMONELLA PATHOGENICITY ISLAND LOCATED AT 92 MINUTES ON THE CHROMOSOME MAP OF SALMONELLA-ENTERICA SEROVAR TYPHIMURIUM LT2

Using a genomic approach, we have identified a new Salmonella pathogen icity island, SPI-4, which is the fourth Salmonella pathogenicity isla nd to be identified, SPI-4 was located at 92 min on the chromosome map and was flanked by the ssb and soxSR loci, The DNA sequence covering the entire SPI-4 and both boundaries was determined. The size of SPI-4 was about 25 kb and it contains 18 putative open reading frames (ORFs ), Three of these ORFs encode proteins that have significant homology with proteins involved in toxin secretion. Another five ORFs encode pr oteins that have significant homology with hypothetical proteins from Synechocystis sp. strain PCC6803 or Acinetobacter calcoaceticus. The r est of the ORFs encode novel proteins, one of which has five membrane- spanning domains. SPI-4 is likely to carry a type I secretion system i nvolved in toxin secretion. Furthermore, a previously identified locus (ims98), which is required for intramacrophage survival, was also map ped within the SPI-4 region. These findings suggested that SPI-4 is ne eded for intramacrophage survival.