Ask A Scientist© Molecular Biology Archive

name         Dale
status       student
age          19

Question -   I read that certain deep sea fishes have spots of
bioluminescence directly under their eye, this
made possible by a colony of luminescent bacteria living there.  How do the
bacteria manage to get into this spot in every fish?  Or are there just
some fish with this spot
and some without, without actual regard as to which species it is but
rather just which fish was lucky enough to meet up
with some bacteria?
------------------------------
I searched the literature for this intreaguing
question. Below is a fragment of an abstract from an
article published in Nature (1993) 363:154-156. Maybe
the introduction of the paper will tell you more.
Another article that may be worth checking is
'light organ symbiosis' in Critical Reviews of
Microbiology (1993) 19:191-216. In the abstract of
this review it is stated that most bacteria present in
light organs are also free-living. This suggests a
'catch-and-carry' symbiosis.

[From Nature (1993) 363:154-156]
"Bioluminescent symbioses range from facultative
associations to highly adapted,  apparently obligate
ones. The family Anomalopidae (flashlight fishes)
encompasses five  genera of tropical reef fishes that
have large suborbital light organs. The suborder
Ceratioidei (deep-sea anglerfishes) contains 11
families. In nine of these, females have a
bioluminescent lure that contains bacterial symbionts.
In all other fish light-organ  symbioses (occurring in
10 families in 5 orders), the symbionts belong to
three
  Photobacterium species; nonsymbiotic luminous
bacteria are Vibrio species. The bacteria are
extracellular and tightly packed in tubules that
communicate with the exterior, releasing bacteria into
the gut of the host or the surrounding sea water. The
released  bacteria are usually cultivable and can
contribute to planktonic populations. Although
anomalopids release bacteria and ceratioids have pores
that would allow release, the fate
  of these bacteria is unknown and they cannot be
cultured by standard isolation techniques"

Trudy Wassenaar
Curator of the Virtual Museum of Bacteria
=========================================================
I searched the literature for this intreaguing
question. Below is a fragment of an abstract from an
article published in Nature (1993) 363:154-156. Maybe
the introduction of the paper will tell you more.
Another article that may be worth checking is
'light organ symbiosis' in Critical Reviews of
Microbiology (1993) 19:191-216. In the abstract of
this review it is stated that most bacteria present in
light organs are also free-living. This suggests a
'catch-and-carry' symbiosis.

[From Nature (1993) 363:154-156]
"Bioluminescent symbioses range from facultative
associations to highly adapted,  apparently obligate
ones. The family Anomalopidae (flashlight fishes)
encompasses five  genera of tropical reef fishes that
have large suborbital light organs. The suborder
Ceratioidei (deep-sea anglerfishes) contains 11
families. In nine of these, females have a
bioluminescent lure that contains bacterial symbionts.
In all other fish light-organ  symbioses (occurring in
10 families in 5 orders), the symbionts belong to
three
  Photobacterium species; nonsymbiotic luminous
bacteria are Vibrio species. The bacteria are
extracellular and tightly packed in tubules that
communicate with the exterior, releasing bacteria into
the gut of the host or the surrounding sea water. The
released  bacteria are usually cultivable and can
contribute to planktonic populations. Although
anomalopids release bacteria and ceratioids have pores
that would allow release, the fate
  of these bacteria is unknown and they cannot be
cultured by standard isolation techniques"

Trudy Wassenaar
Curator of the Virtual Museum of Bacteria
=========================================================
APPEND
NEWTON BBS Bioluminescent Bacteria and Fish ---Molecular


In nine of these, females have a bioluminescent lure that contains bacterial 
symbionts. Not to harp on the subject, but as this
sentence within your response indicates, there is clearly a 'rule' as to where
these luminous bacteria will set up shop, so to say.  I would expect the female
anglers to be larger, as that is usually the case with such species, so it
might be possible that the larger female presence allows for them to obtain
these bacteria in a way that the males do not.  However, this is merely an idea
that I thought of when first reading your response.  Although I have
consistently learned over the years that there is no 'always' or 'never' in
biology, could it be that there is some circumstance which would lead to these
luminous bacteria congregating in the angler tip of females of a particular 9
species, and not in the tips
of females in the other species or in males of any species whatsoever?  Or
could it be that it is completely random, and there
have just been such a small amount of evidence to really see the big
picture, because there are so few specimens of these sorts of animals studied?
------------------------------------------------
Hi Dale,
You are right, 'always' and 'never' are very strong
concepts in biology, however host-specificity in
bacteria can be very definite. It is best described
for bacterial pathogens that colonize some hosts but
not others, and cause disease in some (or all) of the
hosts they colonize. Commensals and symbionts also
display host-specificity, dictated by adhesin-receptor
interactions, and less well-defined mechanisms. In the
case of luminous bacteria in fish light organs, my
guess is that this is a specific interaction, where
only certain fish species 'allow' the presence of only
certain types of  bacteria. In this particular case it
even seems gender specific. I couldn't find literature
that described the mechanism behind it, but you can
guess this may be hormone-dependent (do male fishes
produce a light-organ all together?), or receptor
specific.

In conclusion, the interaction of these fish and their
bacteria is probably specific. The way these bacteria
find their right host may be by chance. It is likely
that both bacteria and host profit from the situation.

Trudy Wassenaar
=========================================================