Regulation of Virulence Genes Salyers & Whitt: Bacterial Pathogenesis: A Molecular Approach ASM Press, 1994 Dorman, C.J: Genetics of Bacterial Virulence. Blackwell Scientific Publications, 1994

Virulence Factors Invasion Penetration Protection Nutrition Dissemination

Overview Gene Regulation Genetic Organization In Vitro Methods for Studying Virulence Factors Protein Secretion

Environmental Pressures Influencing Virulence Factor Production Osmolarity O 2 Concentration CO 2 Concentration pH O 2 and N intermediates Lack of nutrients Inorganic ion concentrations

Environmental Modulation vs Phase Variation Antigenic Variation

CHANGE IN DNA SEQUENCE Gene AmplificationGene Rearrangement CHANGE IN NUMBER OF TRANSCRIPTS ActivatorsRepressors CHANGE IN AMOUNT OF ACTIVE GENE PRODUCT Covalent Modification Proteolytic Cleavage Binding to Host Cell Proteins

Genetic Variation in Pathogenic Bacteria Homologous Recombination  Slip Strand Mispairing  Opa – N. gonorrhoeae – CTCTT  LPS – H. influenzae – CAAT  Pilin – H. Influenzae – TA Site-specific Recombination  Gene Inversion  Flagellin - S. typhimurium

Phase Variation I: Gene Inversion

Stages in interaction of N. gonorrhoeae with cultured mammalian cells

pilE Antigenic Variation

Phase Variation II: Slipped Strand Mispairing

Transcriptional Regulation Fur repressor (ferric uptake repression) AraC transcriptional activator family LysR transcriptional activator family Two-Component Regulatory Systems

Ara C Family

LysR Transcriptional Activator Family

Membrane Signal Transduction

Genetic Organization of Virulence Factors: Sources Plasmid transformation (horizontal gene transfer) e.g Shigella flexneri, Salmonella spp, Yersinia spp, Clostridium tetani. Phage lysogeny e.g C. botulinus toxins, S. pyogenes, C. diphtheria toxin, Cholera toxin Pathogenicity Islands Transposons Integrons

Pathogenicity Islands Carriage of many virulence genes Association with pathogenic species Different GC content compared to rest of host genome Association with tRNA genes and/or insertion sequence elements, suggesting phage origin. Presence of transposable elements Instability