After seeing this video I am curious to know why the free living bacteria produce light. What advantage will they have ? Or is it just an "unintentional" result of one of their pathways ?
'There are many bacterial species that are able to emit light. The ecological benefit for a fish or squid living in a symbiotic association with luminescent bacteria has been established. The host organism can use the light emitted by bacteria to attract prey, escape from predators or for communication. However, it is not understood what specific benefit symbiotic bacteria derive from producing light.'
'Communication (quorum sensing) plays a role in the regulation of luminesence in many species of bacteria. Using small extracellularly secreted molecules, they turn on genes for light production only at high cell densities.'
Go for the below link, you will find an article on "How do marine bacteria produce light, why are they luminescent, and can we employ bacterial bioluminescence in aquatic biotechnology?"
also there is an article in wikipedia on Bioluminescence en.wikipedia.org/wiki/Bioluminescence