I love all living things (in a total non-hippy way), but it’s clear that I’ve my preferences, and prokaryotes don’t get as much coverage as Eukarya around here usually. So here’s a bacterium, and what’s cooler than a normal bacterium? A bacterium that glows in the dark. Yes, Vibrio fischeri is a gram-negative marine bacterium, widely studied for its bioluminescence. Not only it lights up, but it’s also capable of symbiosis with marine animals like fishes and squids, which use its bioluminescence to their own advantage, and have co-evolved with these bacteria so that it’s easier for the microorganisms to colonize specific organs in their bodies. As far as I know, it’s also used in ecotoxicology studies, probably in part because it should be easier to check the growth of a glowing bacterium than the growth of a non-shiny one.