title: STM2209-STM2208 (opvAB): a phase variation locus of Salmonella enterica involved in control of O-antigen chain length.
abstract: STM2209 and STM2208 are contiguous loci annotated as putative protein-coding genes in the chromosome of Salmonella enterica. Lack of homologs in related Enterobacteria and low G+C content suggest that S. enterica may have acquired STM2209-STM2208 by horizontal transfer. STM2209 and STM2208 are co-transcribed from a promoter upstream STM2209, and their products are inner (cytoplasmic) membrane proteins. Analysis with the bacterial adenylate cyclase two-hybrid system suggests that STM2209 and STM2208 may interact. Expression of STM2209-STM2208 is subjected to phase variation in wild type Salmonella enterica serovar Typhimurium. Switching frequencies in LB medium are 6.1×10(-5) (OFF→ON) and 3.7×10(-2) (ON→OFF) per cell and generation. Lack of DNA adenine methylation locks STM2209-STM2208 in the ON state, and lack of the LysR-type factor OxyR locks STM2209-STM2208 in the OFF state. OxyR-dependent activation of STM2209-STM2208 expression is independent of the oxidation state of OxyR. Salmonella cultures locked in the ON state show alteration of O-antigen length in the lipopolysaccharide, reduced absorption of bacteriophage P22, impaired resistance to serum, and reduced proliferation in macrophages. Phenotypic heterogeneity generated by STM2209-STM2208 phase variation may thus provide defense against phages. In turn, formation of a subpopulation unable to proliferate in macrophages may restrain Salmonella spread in animal organs, potentially contributing to successful infection.
authors.affiliation: Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Cota
authors.forename: Anne Béatrice
authors.initials: AB
authors.lastname: Blanc-Potard
authors.forename: Josep
authors.initials: J
authors.lastname: Casadesús
mesh_terms: D000818:Animals; D017100:Bacteriophage P22 / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008264:Macrophages / Q000382:microbiology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D019081:O Antigens / Q000737:chemistry / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012329:RNA, Bacterial / Q000235:genetics; D012481:Salmonella Infections, Animal / Q000209:etiology; D012486:Salmonella typhimurium / Q000235:genetics* / Q000276:immunology / Q000472:pathogenicity / Q000821:virology; D014774:Virulence / Q000235:genetics / Q000276:immunology
chemical_list: D019081:O Antigens; D012329:RNA, Bacterial