The marine bacterium V. fischeri exists naturally either in a free-living planktonic state or as a symbiont of certain luminescent fish or squid (Ruby & Nealson, 1976, Ruby & McFall-Ngai, 1999). The bacteria colonise specialised light organs in the fish or squid, which cause them to bioluminesce. Luminescence in the fish or squid is thought to be involved in the attraction of prey or even as camouflage. During the nocturnal feeding of the squid Euprymna scolopes, luminescence from the light organ is directed towards the sea floor and is modulated by the squid to match the intensity of moonlight, therefore preventing a shadow of the squid on the sea floor (Visick & McFall-Ngai, 2000). The source of the luminescence is the bacteria themselves. In the marine environment, the bacteria only luminesce when colonising the light organs and do not emit light when in the free-living state. It makes good evolutionary sense for the bacteria to tightly regulate bioluminescence as the mechanism by which light is produced is very energy intensive. Research carried out to answer the question of how V. fischeri regulates bioluminescence led to the discovery of bacterial quorum sensing via N-acyl-L-homoserine lactones (AHLs).

Molecular mechanism of QS in V. fischeri

Structures of AHLs

Other organisms with V. fischeri type QS systems