11680891
Description
| Question | Answer |
| V. fischeri | bioluminescent bacterium in symbiosis with E. scolopes squid colonizes juvenile squid, which is VERY species specific --> develops light organ squid hides during day, forages at night light from V. fischeri in light organ hide squid's shadow and hide it from predators! |
| bacterial luciferase | a mixed function oxidase, composed of alpha and beta subunits uses three different reactions to make light antibiotics that block tx or tn stop luminescence --> genes encoding luciferase are transcribed differently in different parts of the growth curve |
| acyl homoserine lactone (AHL) | autoinducer of luminescence activity acyl group varies by species is recycled back in and out of cell --> when conc. high enough, triggers expression of luminescence genes |
| How to determine genes for luminescence | Take sample of v. fischeri --> make genomic DNA library --> transform e. coli while selecting for presence of plasmid --> isolate plasmid with luminescence genes by screening colonies for light production in the dark! |
| lux operon tx | same gene cluster confers both making luminescence and sensing it: strong positive feedback loop!!! LuxI synthesizes AHL, which is really hydrophobic --> diffuses freely outside and accumulates --> at a threshold concentration, AHL diffuses back inside and binds to activator LuxR --> lux operon tx increased |
| luxL operon | synthesizes AHL, which in turn promotes tx of lux operon (increasing LuxR) also transcribes Luciferase, which undergoes various rxns to produce light |
| LuxR proteins | when bound to AHL, fold correctly and dimerize --> bind upstream of lux genes to activate tx when not bound to AHL, are in an inactive monomer conformation and are rather unstable --> tx off |
| different species AHL | differ by acyl chain length and B carbon modification |
| gram negative vs gram positive quorum sensing | only gram negative are AHL-mediated, all of the molecules are different for gram positive (use AIPs instead) |
| Quorum sensing in gram positive bacteria | long precursor peptide is translated, during export it is processed to mature signaling form (AIPs) --> sensed by a histidine kinase, after a certain threshold the HK activity changes --> population dependent effects mediated by downstream regulators |
| AIP variations | can be linear or cyclized **structural similarities but different sequences --> cannot be detected by receptors on different strain!** |
| S. aereus virulence gene tx | AgrD precursor processed by AgrB into short cyclic AIP, secreted outside --> AgrC HK senses AIP outside, changes activity at high levels --> change activates AgrC, which phosphorylates --> AgrC-P activates tx of agr operon (positive feedback) and tx of virulence genes |
| furanone compounds | disrupt quorum sensing by affecting biofilms and reducing virulence of some species halogenated versions of these bind to LuxR homologs --> block tx of lux operon has rather unpredictable effects since virulence can occur at high or low cell density |
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