luminescence in fish by Vibrio

Yves Dessaux Yves.Dessaux at isv.cnrs-gif.fr
Thu Jun 12 07:34:23 EST 1997

In article <5kd4in$2cl at dfw-ixnews6.ix.netcom.com>, epiphany at ix.netcom.co 
>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.



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