Survey
* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project
Download No Slide Title
Document related concepts
no text concepts found
Transcript
Phase Variation Adaptive process by which bacteria undergo frequent and reversible phenotypic changes resulting from genetic alterations in their genome. From: Hallet 2001 Curr. Opin. Microbiol. 4:570. Commonly regulates surface exposed antigenic structures (e.g. outermembrane LPS, lipoproteins, pili, flagella) Binary Switch: “On” or “Off” Phase Variation Phase variation is generally a random event ocuring at a high frequency (>105 per generation) Generates phenotypically heterogeneous population Programmed event: genome is organized so that certain events are more likely to occur. Henerson et. al. 1999 Mol. Microbiol. 33:919 Phase Variable Expression of Escherichia coli Surface Protein, Ag43 Phase ‘ON’ Ag43+ Phase ‘OFF’ Ag43- Immunofluorescence Microscopy with Ab to Ag43 Escherichia coli with P pili P pili Thick rod (PapA subunits), followed by a thinner tip fibrillum (PapE subunits) with PapG adhesin at the tip. P pili mediate pyelonephritic E. coli binding to receptor on human kidney cells. Type1 Fimbria Type 1 fimbriae Thick rod (FimA subunits), followed by a thinner tip fibrillum (FimG & FimF subunits) with FimH adhesin at the tip. Type 1 fimbriae mediate uropathogenic E. coli binding to receptor on bladder epithelial cells. Phase contrast E. coli expresses either P pili or Type 1 Fimbriae,not both Anti-P pili staining Anti-Type 1 Fimbriae staining Hypothesis: Production of P pili inhibits the production of Type 1 fimbriae Type 1 Fimbriae Gene Cluster Mechanisms of Phase Variation of Type 1 Fimbriae DNA Inversion - site-specific recombination Phase ‘ON’ fimB fimE fimA Lrp sites IHF IR IHF IR IHF fimE FimB FimE 37-40oC <37oC Lrp sites fimB IHF higher specific activity IR Phase ‘OFF’ IHF HNS Lrp IR fimA FimB and FimE share homology with lambda integrase family of site-specific recombinases Mechanisms of Phase Variation of P pili Differential methylation - Epigenetic (phenotype differs but the genotype does not) PapB inhibits production of type 1 fimbriae control papB papI Switch locked ФONХ PapB blocks phase variation of fimA Does PapB inhibit FimB or FimE mediated phase variation? Phase ‘ON’ fimB fimE fimA Lrp sites IHF IR IHF IR IHF fimE FimB FimE 37-40oC <37oC Lrp sites fimB IHF higher specific activity IR Phase ‘OFF’ IHF HNS Lrp IR fimA Method to measure the frequency of FimB and FimE mediated phase variation FimB phase variation FimE phase variation PapB blocks FimB mediated phase variation in vivo Two Models for how PapB Inhibits FimB Phase Variation PapB PapB fimB FimB FimB Switching Switching PapB has a small effect on transcription of fimB PapB inhibits FimB recombination Mechanisms of Phase Variation DNA Inversion - site-specific recombination (e.g. type 1 fimbriae E. coli & flagellum S. typhimurium) & RecA-dependent homologous recombination (e.g. type IV pili N. gonorrhoeae) Differential Methylation - epigenetic (e.g. P pili and Ag43 of E. coli) Slipped-strand mispairing - repetitive DNA segments (e.g. Opa adhesins of N. gonorrhoeae, many surface proteins in B. pertussis and H. pylori)
Related documents