Bacterial Quorum Sensing

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Bacterial Quorum Sensing
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Quorum Sensing Is Central to Symbiosis
Eberhard, et al., 1981 Crookes et al., Science
303235
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Quorum Sensing Population Density-Dependent
Gene Regulation
growth
time
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Quorum Sensing Population Density-Dependent
Gene Regulation
growth
Quorum sensing-regulated gene expression
time
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Behaviors controlled by QS

• Structuring of multicellular communities
• Stress survival
• Production of
• Antibiotics
• Pigments
• Host tissue degrading enzymes

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QS signals in Bacteria
Signals are diverse, most are synthesized by
specific known enzymes
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Enzymatic synthesis of QS signals
AHL synthase, LuxI-like
AI-2 in Gram-, Gram bacteria
AHLs are common in Gram- bacteria
Keller et al. Nature Reviews Microbiology
published online 27 February 2006
doi10.1038/nrmicro1383
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Detection of QS signals in V. fischeri
LuxI AHL synthase (makes AHLs) LuxR AHL
receptor (detects AHLs) luxCDABE encodes
production of light in V.fischeri Red triangle
AHLs that diffuse in and out
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Examples of AHL-mediated QS

• Vibrio fischeri
• light production
• Vibrio cholera
• When grows on chitin, can acquire DNA from
  environment. Requires AHLs to be able to grow on
  chitin
• Pseudomonas aeruginosa
• virulence, Fe acquisition, stress response, etc.
  Over 200 genes
• Yersinia enterocolitica
• is activated in foods, possibly involved in
  enzyme production, biofilm formation
• Salmonella, E. coli, Shigella
• do not make AHLs themselves (have lost the AHL
  synthase gene)
• detect AHLs produced by other bacteria (have
  gained a new AHL receptor gene)

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Other examples of QS in Gram -

• AI-2 signal in many G-, G bacteria. A universal
  language?
• Non-AHL unknown signals in Xyllela, Xanthomonas
  (water-, air-, soil- borne pathogens of citrus
  and grapes)
• Volatile esters of fatty acids in Ralstonia, a
  pathogen that causes wilt in tomato

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Quorum sensing in Gram bacteria

• Signals, detection appear more diverse
• Gamma-butyrolactone in Streptomyces controls
  production of aerial hyphae and antibiotics
• Myxococcus uses a mixture of aminoacids to
  initiate sporulation (more later)
• Peptide signals in Bacillus, Staph control
  competence, virulence

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Degradation of AHL QS signals

• AHLs can be degraded by enzymes produced by soil
  bacteria
• Bacillus AHL lactonase, AiiA (cleaves lactone
  ring)
• AHL acylases made by several soil bacteria.
  Cleaves of acyl side chain
• Ecological functions of degrading AHLs
• C, N sources
• scrambling communication in other bacteria.
• turn-over of the signal

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QS and Fratricide

• Fratricide killing off siblings
• Bacillus subtilis can form spores (resting
  structures) in response to nutrient deprivation
• If nutrient deprivation is brief, a spore is at
  disadvantage
• Fratricidal cannibalism precedes spore formation
• In response to nutrient limitation, Spo0A is
  induced in 1/2 of cells. At this stage, the
  population is not yet fully committed to spore
  formation
• Spo0A ON --gt spore formation,
• Spo0A OFF --gt no spore formation
• Spo0A ON --gt produce and secrete toxin that kills
  and lyses Spo0A OFF cells.
• When all the Spo0A cells are lysed and digested,
  the entire remaining population will form spores
• Spo0A ON also make produce membrane-bound
  immunity protein that neutralizes the lysing
  toxin
• The immunity protein also functions in QS signal
  transduction
• Streptococcus pneumoniae
• Peptide QS signal induces competence also causes
  lysis of sibling cells
• Surviving cells may benefit from acquiring DNA,
  and by the release of host tissue degrading
  enzymes

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Algal Furanones what can we learn from nature
Observation The red seaweed Delisea pulchra is
remarkable free of bifouling
S. Kjelleberg
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Algal Furanones what can we learn from nature
Algal halogenated furanones appear capable of
inhibiting bacterial QS.
S. Kjelleberg
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Algal Furanones what can we learn from nature
S. Kjelleberg
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This is cute, but why exactly are we spending
time on QS?

• What does QS mean to ecology of pathogens?
• Can we manipulate QS to our advantage?
• Isnt it better/easier to just kill the pathogens
  with antibiotics instead worrying about
  communication?