Bioluminescence is the process by which living organisms emit light. This phenomenon occurs in many species of bacteria, fungi and animals (both invertebrates and vertebrates). The mechanisms of luminescence in all of these groups of organisms are generally similar, though some details (like the substrates for the chemical reaction) may vary considerably among different species. Interestingly, it seems that bioluminescence has appeared several times independently during the evolution of life forms (Rees et al. 1998).
Bacterial bioluminescence occurs mainly (though not exclusively) in species living in marine environments (Nealson 1978). Importantly, light-emitting bacteria are the most abundant and widespread of luminescent organisms (Meighen 1994). Two bacterial species able to emit light, Vibrio fischeri and Vibrio harveyi, have been investigated intensively, and most of this article will concern these bacteria. V. fischeri is a symbiotic bacterium living in the light organs of fish of the family Monocentridae and of the cephalopods Sepiola and Euprymna (Fitzgerald 1977, Ruby 1996). V. harveyi is a free-living bacterium, though it may also be found occasionally on the surface of marine animals or in their gut (Baumann et al. 1973, Ruby & Morin 1979).
Since the biochemical mechanism of bacterial luminescence and the genetic regulation of this process have recently been reviewed by others (Bassler & Silverman 1995, Rees et al. 1998, Swift et al. 1998, Winans & Bassler 2002), in this article we will summarize briefly our current knowledge about the biochemistry and genetics of light emission by bacteria. We will then focus on the biological role of bacterial luminescence and possible evolutionary drives in the early stages of its development. Finally, we will discuss possible applications of luminescent bacteria in aquatic biotechnology.