luminescence in fish by Vibrio

Karl Roberts kr1 at PGSTUMAIL.PG.CC.MD.US
Thu Jun 12 08:35:49 EST 1997

	The relationship between luminescent bacteria and their host is
symbiotic in nature.  Some fish have such relationships only in one sex,
implying that the light emitted may be used in mate recognition behavior,
others may utilize bacterial luminescence to attract prey, and some may
utilize the light organ structures in schooling behavior.  Fish such as
Photoblepharon (the flashlight fish) even have a diaphram-like structure
which can be used to cover the light organ, allowing them to signal.
While bacteria can live in dead fish, the relationship is mutualistic, so
a living host is the obvious choice. I hope this helps.

On 12 Jun 1997, Yves Dessaux wrote:

> In article <5kd4in$2cl at dfw-ixnews6.ix.netcom.com>, epiphany at ix.netcom.co 
> says...
> >
> >Does anyone have any ideas as to why it may be evolutionarily
> >advantageous for Vibrio harveyi and fischeri to cause luminescence in
> >certain species of fish and squid?  Would this be beneficial to the
> >Vibrio, the fish, or both?  Is it harmful to the fish?  Is this
> >response dependant on the fish's environment?  Does the fish that the
> >Vibrio inhabit have to be alive- if not, does the response of
> >luminescence continue after death?  Are these Vibrio dangerous to
> >humans in any way?  Do thses Vibrio species inhabit fish that are
> >normally consumed by humans?  Any deas or sources on this topic would
> >be greatly appreciated!  Thanks.  Ana  
> I am not a specialist of these questions. However, here is 
> what I know:
> Luminescence is produced by the activity of the product of 
> the lux gene of Photobacterium (ex: Vibrio) fischerii. This 
> activity is dependent on the concentration of bacteria, and
> "starts" only when a sufficient concentration of bacteria is
> raised (this phenomenon is called quorum sensing).
> Cloned lux gene is epresssible in E. coli, and under appropriate
> expression conditions, it allows E. coli "to glow in the dark"
> when you grow the bacteria on rich medium. Consequently, lux
> expression per se is not dependent on whether the fish is alive or
> not! In addition, I do not beleive that Photobacterium fisherri is 
> regarded as a pathogen for humans of animals...
> Now, to answer the "why" quetions, I do not think that this beneficial 
> directly for the bacteria but the whole system might be a sort of 
> symbiosis. The light emited by the bacteria might afraid the fish 
> predators while the bacteria find in the "fish environement" the 
> nutriments that they need to grow. It is only a speculation, and
> this later part of my mail needs to be checked.
> Sincerely,
> Yves

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