SPI-9 of Salmonella enterica serovar Typhi is constituted by an operon positively regulated by RpoS and contributes to adherence to epithelial cells in culture.
The genomic island 9 (SPI-9) from Salmonella enterica serovar Typhi (S. Typhi) carries three ORFs (STY2876, STY2877, STY2878) presenting 98 % identity with a type 1 secretory apparatus (T1SS), and a single ORF (STY2875) similar to a large RTX-like protein exhibiting repeated Ig domains. BapA, the Salmonella enterica serovar Enteritidis orthologous to S. Typhi STY2875, has been associated with biofilm formation, and is described as a virulence factor in mice. Preliminary in silico analyses revealed that S. Typhi STY2875 ORF has a 600 bp deletion compared with S. Enteritidis bapA, suggesting that S. Typhi STY2875 might be non-functional. At present, SPI-9 has not been studied in S. Typhi. We found that the genes constituting SPI-9 are arranged in an operon whose promoter was up-regulated in high osmolarity and low pH in a RpoS-dependent manner. All the proteins encoded by S. Typhi SPI-9 were located at the membrane fraction, consistent with their putative role as T1SS. Furthermore, SPI-9 contributed to adherence of S. Typhi to epithelial cells when bacteria were grown under high osmolarity or low pH. Under the test conditions, S. Typhi SPI-9 did not participate in biofilm formation. SPI-9 is functional in S. Typhi and encodes an adhesin induced under conditions normally found in the intestine, such as high osmolarity. Hence, this is an example of a locus that might be designated a pseudogene by computational approaches but not by direct biological assays.
Laboratorio de Genética y Patogénesis Bacteriana, Departamento de Ciencias Biológicas, Facultad de Ciencias Biológicas, Universidad Andres Bello, República 217, Santiago, Chile.
Juan C
JC
Velásquez
Laboratorio de Patogénesis Molecular y Antimicrobianos, Facultad de Medicina, Universidad Andres Bello, Echaurren 183, Santiago, Chile.
Alejandro A
AA
Hidalgo
Laboratorio de Patogénesis Molecular y Antimicrobianos, Facultad de Medicina, Universidad Andres Bello, Echaurren 183, Santiago, Chile.
Nicolás
N
Villagra
Laboratorio de Genética y Patogénesis Bacteriana, Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Santos Dumont 964, Independencia, Santiago, Chile.
Carlos A
CA
Santiviago
Laboratorio de Patogénesis Molecular y Antimicrobianos, Facultad de Medicina, Universidad Andres Bello, Echaurren 183, Santiago, Chile.
Guido C
GC
Mora
Laboratorio de Genética y Patogénesis Bacteriana, Departamento de Ciencias Biológicas, Facultad de Ciencias Biológicas, Universidad Andres Bello, República 217, Santiago, Chile.
Juan A
JA
Fuentes
D018829:Adhesins, Bacterial / Q000235:genetics; D001422:Bacterial Adhesion / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D018441:Biofilms / Q000254:growth & development; D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D004847:Epithelial Cells / Q000382:microbiology*; D004926:Escherichia coli / Q000235:genetics; D044404:Genomic Islands / Q000235:genetics*; D006801:Humans; D012477:Salmonella enteritidis / Q000235:genetics / Q000472:pathogenicity; D012485:Salmonella typhi / Q000235:genetics* / Q000472:pathogenicity*; D012808:Sigma Factor / Q000235:genetics*; D000069177:Type I Secretion Systems / Q000235:genetics*; D037521:Virulence Factors / Q000235:genetics
D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; D012808:Sigma Factor; D000069177:Type I Secretion Systems; D037521:Virulence Factors; C069567:sigma factor KatF protein, Bacteria