Vibrio fischeri is a light-emitting bacterium. This is called bioluminescence. Many animals and plants that emit light get it from the bioluminescent microbes they work with. This also applies to the Hawaiian bobtail squid (Euprymna scolopes) which works closely with Vibrio fischeri.
Vibrio fischeri is a light-emitting bacterium. This is called bioluminescence. Many animals and plants that emit light get it from the bioluminescent microbes they work with. This also applies to the Hawaiian bobtail squid (Euprymna scolopes) which works closely with Vibrio fischeri.
Counter-illumination
The Hawaiian bobtail squid (Euprymna scolopes) is native to the central Pacific Ocean, where it occurs in shallow coastal waters off the Hawaiian Islands. It’s a tiny squid species. Adults reach up to just 3cm in mantle length and weigh just 2,67 grams. The hatchlings weigh just 0.005g. The squid hunts for shrimp at the surface of the water at night. Due to the moonlight, is creates a silhouette that predators from below would easily spot. The squid therefore lives in a symbiotic relationship with the bioluminescent bacteria Vibrio fischeri, which inhabits a special light organ in the squid's mantle. The bacteria are fed a sugar and amino acid solution by the squid, and in return produce light. This bioluminescence hides the squid's silhouette when viewed from below by matching the amount of moonlight hitting the top of the mantle. This is called counter-illumination.
Safety in numbers
Vibrio fischeri bacteria live mainly in special light organs of the Hawaiian bobtail squid (Euprymna scolopes). However, they are also found free-living in the seawater. However, they do not produce any light there. Logical, because otherwise they would be an easy meal. Vibrio only emit light when there are with enough of their species, for example in the light organs of the squid. The bacterium "knows" that it is with enough other bacteria through a process called quorom sensing. The bacteria produce substances called autoinducers. As soon as this substance reaches a certain threshold value, specific genes in the Vibrio bacteria are switched on and they start to emit light. And that threshold value is only reached when the bacterial colony has reached the right density. For instance, inside the light organs of the squids.