Aliivibrio fischeri (also called Vibrio fischeri) is a Gram-negative, rod-shaped bacterium found globally in marine environments. This species has bioluminescent properties, and is found predominantly in symbiosis with various marine animals, such as the Hawaiian bobtail squid. It is heterotrophic, oxidase-positive, and motile by means of a single polar flagella. Free-living A. fischeri cells survive on decaying organic matter. The bacterium is a key research organism for examination of microbial bioluminescence, quorum sensing, and bacterial-animal symbiosis. It is named after Bernhard Fischer, a German microbiologist. Ribosomal RNA comparison led to the reclassification of this species from genus Vibrio to the newly created Aliivibrio in 2007. However, the name change is not generally accepted by most researchers, who still publish Vibrio fischeri (see Google Scholar for 2018-2019). Genome The genome for A. fischeri was completely sequenced in 2004 and consists of two chromosomes, one smaller and one larger. Chromosome 1 has 2.9 million base pairs (Mbp) and chromosome 2 has 1.3 Mbp, bringing the total genome to 4.2 Mbp. A. fischeri has the lowest G+C content of 27 Vibrio species, but is still most closely related to the higher-pathogenicity species such as V. cholerae. The genome for A. fischeri also carries mobile genetic elements. Ecology A. fischeri are globally distributed in temperate and subtropical marine environments. They can be found free-floating in oceans, as well as associated with marine animals, sediment, and decaying matter. A. fischeri have been most studied as symbionts of marine animals, including squids in the genus Euprymna and Sepiola, where A. fischeri can be found in the squids' light organs. This relationship has been best characterized in the Hawaiian Bobtail Squid (Euprymna scolopes), where A. fischeri is the only species of bacteria inhabiting the squid's light organ. Symbiosis with the Hawaiian bobtail squid A. fischeri colonization of the light organ of the Hawaiian bobtail squid is currently studied as a simple model for mutualistic symbiosis, as it contains only two species and A. fischeri can be cultured in a lab and genetically modified. This mutualistic symbiosis functions primarily due to A. fischeri bioluminescence. A. fischeri colonizes the light organ of the Hawaiian bobtail squid and luminesces at night, providing the squid with counter-illumination camouflage, which prevents the squid from casting a shadow on the ocean floor. A. fischeri colonization occurs in juvenile squids and induces morphological changes in the squids light organ. Interestingly, certain morphological changes made