Genomic analysis and growth-phase-dependent regulation of the SEF14 fimbriae of Salmonella enterica serovar Enteritidis The GenBank accession number for the sequence reported in this paper is AF239978.

Abstract

Salmonella enterica serovar Enteritidis is a leading cause of food poisoning in the USA and Europe. Although Salmonella serovars share many fimbrial operons, a few fimbriae are limited to specific Samonella serovars. SEF14 fimbriae are restricted to group D Salmonella and the genes encoding this virulence factor were acquired relatively recently. Genomic, genetic and gene expression studies have been integrated to investigate the ancestry, regulation and expression of the sef genes. Genomic comparisons of the Salmonella serovars sequenced revealed that the sef operon is inserted in leuX in Salmonella Enteritidis, Salmonella Paratyphi and Salmonella Typhi, and revealed the presence of a previously unidentified 25 kb pathogenicity island in Salmonella Typhimurium at this location. Salmonella Enteritidis contains a region of homology between the Salmonella virulence plasmid and the chromosome downstream of the sef operon. The sef operon itself consists of four co-transcribed genes, sefABCD, and adjacent to sefD there is an AraC-like transcriptional activator that is required for expression of the sef genes. Expression of the sef genes was optimal during growth in late exponential phase and was repressed during stationary phase. The regulation was coordinated by the RpoS sigma factor.

Analysis of the Hypervariable Region of the Salmonella enterica Genome Associated with tRNA leuX

“…Comparisons of the Salmonella serovar Typhi SPI-10 sequence with other sequenced enteric bacteria revealed remarkable heterogeneity (this study and previous partial sequence data) (21). For example, the gene complements at this locus in Salmonella serovar Typhi and Salmonella serovar Typhimurium are entirely different (Fig.…”

“…In some cases, the mosaic structures of these islands are also reflected in variations in G-C content. For example, the region encompassing the sef fimbrial genes has a particularly low G-C content (34.14% compared to 52.17% in Salmonella serovar Enteritidis PT4, as previously noted [21], and 34.2% in Salmonella serovar Typhi CT18 compared with 52.09% overall in the genome) (Fig. 2).…”

RegR Virulence Regulon of Rabbit-Specific Enteropathogenic Escherichia coli Strain E22

“…It consists of four cotranscribed genes encoding the major subunit (SefA), chaperone (SefB), usher (SefC), and minor subunit (SefD) of the SEF14 fimbriae (46). The E22 fimbria-like structures that we identified by immunogold electron microscopy using anti-SefA serum have a morphology similar to that of SEF14 fimbriae produced by S. Enteritidis, which play a role in colonization of epithelial cell surfaces (57).…”

“…Four of these genes (sefABCD) appear to form one operon, encoding proteins with similarity, ranging from 59 to 74%, to the fimbrins chaperone and usher of SEF14 fimbriae of Salmonella enterica serovar Enteritidis (Table 3) (46). Strikingly, transcription of sefA, the first gene of the sef operon, was activated 390-fold by RegR.…”

“…SEF14 fimbriae are required for binding of S. Enteritidis to macrophages and are a virulence determinant of Salmonella (58). Interestingly, the expression of Salmonella sefABCD is subject to positive control by the AraC-like transcriptional activator SefR (46).…”