october 28 lab related notes

October 28, 2009 – lab related notes
1) Quorum sensing: ability of some bacteria to change phenotype at different population densities
Phenotype: observed characteristics in an organism
Genotype: set of genes/DNA an organism has
• Many bacteria have genes that are not always present
a) Example: “suicide at high population densities ex: S. pneumonia
 Genes for signal, receptor always on
 When all receptors have signal bound to them Lyt A gene is expressed—death of bacterium
b) Example: Pseudomonas aeruginosa: biofilm of rhamnolipids, pyocyanin made at high population densities
 Signal: homoserine lactone (HSL)
 Genes for signal, receptor always on
 When all receptors have signal bound to them, genes for rhamnolipids and pyocyanin expressed
c) Vibrio fischeri: express luciferase at high population densities= blue/green light
 Genes for signal, receptor always on
 When all receptors have signal bound to them, gene for luciferase expressed
o Have a symbiotic relationship with a squid: eurypmna scolopes( nocturnal, predator& prey)
o Eurypmna scolopes: has “light organ” in head
- Colonized with vibrio fischeri allows high population density of vibrio fischeri- luciferase

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