This gamma-proteobacterium is an aquatic organism with an interesting lifestyle. V. fischeri can be found either free-living or stablishing a symbiotic relationship with diverse hosts (depends on the strain).
The most famous one is that of VF and the hawaiian bobtail squid Euprymna scolopes (the one in the picture), in fact the sequenced strain (ES114) stablishes its relationship with this cephalopod. Among many interesting things this tiny organism (fischeri) colonises the light organ of the squid, providing luminesce to the host, which is used to avoid predation, camouflage and might even be involved in mating.
I have been working a bit with this bacterium and I still find amazing when I walk into the incubator and can collect the plates without swithing the light on…
Recently a paper has been published in BMC Genomics by Chun et al where they create an annotated cDNA library of juvenile squids with and without the symbiont at different time points. They show how different number of genes are expressed at different stages of the colonisation of the light organ.
After mining the data much more will be known about this fascinating relationship.