Lecture 4: Quorum Sensing

  • Created by: chandanee
  • Created on: 03-01-19 12:40
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  • Quorum Sensing
    • Sexual exchange Protecting your niche Combating host defences Population migrations
    • Cell to cell communication: mechanism for GE, OG senses changes in the population density, when pop. reaches a critical size (quorate) behaviour changes.
    • Needs a sensor kinase or response regulator by small diffusible signal mol
    • Gram
      • Gram -
        • N-acylhomserine lactones (NAL), 2A4Q, DSF, C18-FAME
        • E.g Pseudomonas aeru., resistant to Abs, opportunistic. Wound/catheter/eye infections/cystic fibrosis. Lots of protein secretion systems, VFs and control efflux pumps.
        • lasR and lasL genes, las R binds to promoter and releases VFs such as elastase, exotoxin A, catalase, SOD.        RhiR and RhiI also. RhiR controls more VF such as: pyocyanin, elastase, lectins, lipase. Also = pqs genes
        • Mechanism: inability to express rhiAB and produce rhamnolipid surfactants.AAHL sensing controls motility. Biofilms: glue themselves together, form of attachment using pili, prevents dessication. Bilingual = antimicrobials, iron chelators, QS signal mols.
      • Gram +
        • y-Butyrolactones, cyclic peptides, CSP-1
        • Autoinducing peptides (AIPs) lantibiotics, linear peptides, and cyclic peptides
          • Hkp is phosphorylated = RRP > AIP HK RR = reg and target genes = virulence, competence, bacteriocins, sporulation
            • Staphylococcus- controlled by Agr. Virulence determine by growth, colonisation factors and exotoxins. Agr neg = adhesins and Agr + = toxins.
      • Both: AI-2 and furanones
      • Main difference between Gram + and - is that = NEG signal goes in and POS signal cascades
        • Gram - = HK> RR         Gram + = AI peptides go out of the cell, receptor binds, target DNA
        • Versatility: cross signalling, persistence, Ab resistance, filamentation, biofilms, colonisation
    • How and Why?
      • Signal transduction > amp loop> signal synthesis > transducer = multiple gene expression
        • Multiple GE: Ab production, symbiosis, virulence, swimming, conjugation, biofilm, growth inhibition
      • Why communicate? To remain silent to then trigger virulence factors otherwise it can be eradicated by IS
    • QS Inhibition
      • QS Inhibiton - signal mol. biosynthesis and signal mol reception/decoding.
      • Inhibition = by signal synthase inhibitors, receptor antagonists, enzymes, Abs, polymers
      • PAN assay interference compounds = potency, high lipophilicity, metabolic instability, cytotoxicity.


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