Vibrio fischeri

Description and significance
Vibrio fischeri is a curved rod shaped, motile, marine bioluminescent symbiotic bacterium found in the light organs of fish and squid. The bacterium is a heterotrophic facultative anaerobe that shows up as gram negative using the gram stain. It can be found in the upper 1000m of the ocean, living freely, or amongst the mixed biota in the guts of marine animals but is more commonly found as symbionts. V. fischeri bioluminesce only after reaching a certain population density. There has been much studies done on symbiotic relationship between a particular strain of V. fischeri and the Hawaiian bobtail squid, Euprymma scolopes. The nocturnal squid uses the bioluminescence bacteria as camouflage in a 'counterillumination' strategy, while the host provides housing and nutrients for the bacterium.