COMPLEX & MARVELOUS CELLS

1. At low cell density, autoinducers (N-Acyl homoserine lactone molecules) produced by LuxI, diffuse across the cell membrane into the growth medium. 2. As cell proliferation continues, autoinducers in the medium start to accumulate in a confined environment and very low light intensity can be detected. 3. When sufficient autoinducers have accumulated in the medium, they can re-enter the cell where they bind directly to the LuxR protein to activate luxICDABEG expression. 4. High levels of autoinducers activate the luminescent system of A. Fischeri and high light intensity is generated.

Aliivibrio Fischeri is a single-celled, Gram-negative marine bacterium capable of bioluminescence. Heterotrophic and motile employing a single polar flagellum, some colonies float freely in the oceans and feed on decomposing organic matter. Still, very often, this bacterium forms symbioses with marine organisms. Marine organisms contain bioluminescent bacteria to find mates, ward off predators, attract prey or communicate with other organisms. In return, the organism provides the bacteria with a nutrient-rich environment.

The bioluminescence of A. Fischeri is caused by the transcription of the lux operon which consists of seven structural genes. These are organized as luxCDABEGH. The lux operon is induced by population-dependent quorum sensing. The population of A. Fischeri must reach an optimal level to activate the lux system and stimulate light production.