Roles of the outer membrane protein AsmA of Salmonella enterica in the control of marRAB expression and invasion of epithelial cells.
A genetic screen for suppressors of bile sensitivity in DNA adenine methylase (dam) mutants of Salmonella enterica serovar Typhimurium yielded insertions in an uncharacterized locus homologous to the Escherichia coli asmA gene. Disruption of asmA suppressed bile sensitivity also in phoP and wec mutants of S. enterica and increased the MIC of sodium deoxycholate for the parental strain ATCC 14028. Increased levels of marA mRNA were found in asmA, asmA dam, asmA phoP, and asmA wec strains of S. enterica, suggesting that lack of AsmA activates expression of the marRAB operon. Hence, asmA mutations may enhance bile resistance by inducing gene expression changes in the marRAB-controlled Mar regulon. In silico analysis of AsmA structure predicted the existence of one transmembrane domain. Biochemical analysis of subcellular fractions revealed that the asmA gene of S. enterica encodes a protein of approximately 70 kDa located in the outer membrane. Because AsmA is unrelated to known transport and/or efflux systems, we propose that activation of marRAB in asmA mutants may be a consequence of envelope reorganization. Competitive infection of BALB/c mice with asmA(+) and asmA isogenic strains indicated that lack of AsmA attenuates Salmonella virulence by the oral route but not by the intraperitoneal route. Furthermore, asmA mutants showed a reduced ability to invade epithelial cells in vitro.
Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, E-41080 Seville, Spain.
Ana I
AI
Prieto
Sara B
SB
Hernández
Ignacio
I
Cota
M Graciela
MG
Pucciarelli
Yuri
Y
Orlov
Francisco
F
Ramos-Morales
Francisco
F
García-del Portillo
Josep
J
Casadesús
D000818:Animals; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000502:physiology*; D001647:Bile Acids and Salts / Q000494:pharmacology; D015153:Blotting, Western; D002876:Chromosomes, Bacterial / Q000235:genetics; D019295:Computational Biology; D003685:Dehydrocholic Acid / Q000494:pharmacology; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004847:Epithelial Cells / Q000382:microbiology*; D005260:Female; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008826:Microbial Sensitivity Tests; D009876:Operon / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012481:Salmonella Infections, Animal / Q000382:microbiology; D019779:Salmonella enterica / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D014774:Virulence / Q000235:genetics
D001425:Bacterial Outer Membrane Proteins; D001647:Bile Acids and Salts; D003685:Dehydrocholic Acid