Question

Microbiology Mini-Tutorial: Quorum Sensing

Answer 1

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Answer 2

\({\bf{Definition}}\) detection in population density through chemical signaling and the resulting regulation of gene expression

- general mechanism: cell produces AHL signal which diffuses out into the cell until it reaches a point where it will diffuse along its concentration gradient back into the cell. - in bioluminescence:AHL binds to luxR which activates gene expression
- common phenotypes: biofilms, bioluminescence, virulence expression
- characteristics of a good chemical signal:
1. small, easy to make in terms of energy expenditure
2. diffusable across membranes


\({\bf{Bioluminescence}}\)
model organism: gram-neg, bioluminescent Vibrio fischeri which lives symbiotically with marine organisms, regulates the expression of lux genes through quorum sensing.
- signal molecule: N-acyl homoserine lactone (AHL); 3-oxo-hexanoyl homoserine lactone (OHHL)

- lux operon:
luxA/luxB = 2 subunits of luciferase
luxI (capital I)/luxR: regulatory elements
luxE: reductase
luxR: activates transcription
acyl side chains of lux can be modified to confer specific functions

\({\bf{Biofilms}}\) layer of bacterial cells + their polymers, confer protection from enviornment/other organisms

Basic Life Cycle:
1. free-living bacteria attach to surface
2. growth/division into microcolonies
3. maturation of biofilm capable of quorum sensing
4. parts of matrix disperse for further colonization