BIOL 3380 Lecture Notes - Lecture 18: Euprymna Scolopes, Aliivibrio Fischeri, John Woodland Hastings
26 March 2019
BIOL 3380
Microbial Ecology
Quorum Sensing
o Regulation of gene expression in response to fluctuations in population density; regulate
gene expression based on cell density (number bacteria per unit volume)
▪ Way for bacteria to count their numbers
▪ Communication between cells → attribute of multicellular organisms
▪ Communication between bacteria
o Discovery
▪ Vibrio fischeri – bacterium; naturally produces blue light (luminescent)
• Luminescent – production of light
• Fluorescent – need to apply wavelength of light and higher wavelength is
emitted (blue → green)
• Cell Number (log) vs Time
o Lag stage → Exponential / Log Phase → Stationary Phase (high
level)
o Luminescence vs Time
▪ Light would be at lag stage, then increase dramatically
▪ Per cell, light is decreasing during lag stage since light is
staying same but population is growing
▪ During almost stationary phase, there is dramatic
increase in light production
• Light production requires 10,000 to 100,000 ATP/sec (very expensive)
▪ Woody Hastings’ Hypotheses
• 1) Cell Density
o Signaling between bacteria
• 2) Inhibitor is being degraded as bacteria grew
• 3) Activation
o Log Cell Number vs Time vs Luminescence
o Took supernatant from stationary stage (liquid around cells) and
placed it in lag stage
▪ If activator, luminescence would occur right away
(beginning in lag phase)
o Squid and Luminescence
▪ Euprymna scolopes – squid
• V fischeri Cell Number
o In water – 5 cells/mL ➔ no light
o In squids’ light organ - 1010 cells/ml ➔ light
• Squid are born sterile (no vibrio fischeri) → when they push water
through light organ, organ recognizes and keeps only light producing
bacteria
• Squid feed at night and in shallow water → predators are on sandy
bottom ➔ uses bacteria for counter illumination
