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PRODUCTION OF LIGHT BY
LIVING ORGANISMS
LIGHT IS REALIZED BY
ENERGY DERIVED FROM A
CHEMICAL REACTION
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NOT phosphorescence, NOT iridescence
Most of the deep sea, pelagic species
show the phenomenon
thousands of square miles of the ocean
shine with the light of bioluminescent
bacteria in the “milky sea effect".
The chemical luciferin (a pigment) reacts
with Oxygen to create light, and luciferase
(an enzyme) acts as a ctalyst of the
reaction, sometimes mediated by cofactors
such as Calcium ions or ATP.
The chemical reaction can occur either
inside or outside the cell.
In bacteria, the expression of genes related
to bioluminescence is controlled by an
operon (Lux operon)
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Most marine light-emission is in the blue and green light spectrum, the
wavelengths that pass furthest through seawater. However, some loosejawed fish emit red and infrared light, and the polychaete Tomopteris emits
yellow light.
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Aliivibrio fischeri is a Gram - bacterium found globally in the sea world
predominantly in Symbiosis with various marine animals.
Free living A. fischeri are found in very low quantities (almost undetectable)
under a heterotrophic life style (on organics within the water).
They are found in higher concentrations in symbiosis with certain deep sea life
within special light organs; or in the enteral (gut) microbiota of marine animals.
Symbiotic relationships in fishes and
squids appear to have evolved
separately. The most prolific of these
relationships is with the Hawaiian bobtail
squid (Euprymna scolopes).
Free-living A. fischeri in the
ocean are captured by light
organs of juvenile squid and
fishes.
E. scolopes produces mucous to
answer the presence of a
peptidoglycan (of the bacterial
wall). Mucous around the light
organ captures bacteria. V.
fischeri can exclude other
bacteria from the mucous. When
into the mucous, vibrios equips
themselvres with flagella to
migrate into the light organ.
In addition, many bacterial
species reactive to the Oxygen
produce an unsuitable habitat.
The squid produces alide
peroxydases (a mibcrobicide
enzyme) which uses as
substrates the H peroxyde.
V. fischeri has a catalases which
subtracts the peroxyde before it
matches the peroxydases.
After the ciliated ducts of the
light organ, vibrios swim
towards a large theca where
they insert themselves among
the epitelial cells.
Vibrios feed on the host Aa and
sugar and they colonize
completely the space in 10-12 h
from the infection.
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The light organ of certain squid contain reflective plates that intensify
and direct the light produced, due to reflectins (proteins). They
regulate the light to keep the squid from casting a shadow on moonlit
nights, for example.
Sepiolid squids expel 90% of the symbiotic bacteria in its light organ
each morning in a process known as "venting". Venting is
hypothesised to provide the free-living inoculum source for newly
hatched squids.
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The bioluminescence of A. fischeri is caused by transcription of the Lux
operon, induced by population-dependent quorum sensing.
The lux operon is a 9-kilobase fragment of the A. fischeri genome that
controls bioluminescence through the catalyzation of the enzyme luciferase
The luminescence appears to be active more during the nighttime.
The bacterial luciferin-luciferase system is encoded by a set of genes.
In A. fischeri, five genes (luxCDAB(F)E) are involved.
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lux A and lux B code for the components of luciferase
lux CDE codes for a fatty acid reductase complex that makes the fatty acids
necessary for the luciferase mechanism.
Lux C codes for the enzyme acyl-reductase,
lux D codes for acyl-transferase,
and lux E makes the proteins needed for the enzyme (acyl-protein
synthetase),
two genes (LuxR and LuxI) are involved in regulating the OPERON. Several
factors appear to induce and inhibit the transcription of this gene set (light
emission).
Bacterial luciferin is a reduced
riboflavin phosphate (FMNH2) which
is oxidized in association with a longchain aldehyde, oxygen, and a
luciferase.
Luciferase produces blue/green light through the oxidation of
reduced flavin mononucleotide and a long-chain aldehyde by O2.
FMNH2+O2+R-CHO → FMN + R-COOH + H2O + Light
The reduced flavinmononucleotide (FMNH) is provided by the gene LuxG.
To generate the aldehyde needed in the reaction above, three additional
enzymes are needed. The fatty acids needed for the reaction are pulled out
from the fatty acid biosynthesis pathway by the enzyme acyl-transferase.
Acyl-transferase reacts with acyl-ACP to release R-COOH, a free fatty
acid. R-COOH is reduced by a two-enzyme system to an adehyde.
R-COOH+ATP+NADPH→ R-CHO+AMP+PP+NADP+.
bioluminescence is regulated by autoinduction.
An autoinducer is a transcriptional promoter of the enzymes necessary
for bioluminescence. Before the glow can be luminized, a certain
concentration of an autoinducer must be present.
So, for bioluminescence to occur, high colony concentrations of A.
fischeri should be present in the organism.
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krill are bioluminescent animals with photophores.
The light is generated by an enzyme – catalysed reaction,
wherein a luciferin is activated by a luciferase.
Luciferin of many krill species is a fluorescent tetrapyrrole similar but not
identical to dinoflagellate luciferin
the krill probably do not produce this substance themselves but acquire it as part of
their diet, which contains dinoflagellates.
longitudinal section through a ventral
photophore from krill.
Light is produced in the lantern (La)
made up by photocytes processes (B)
and refractive rods. Light produced in
the lantern is reflected by the
reflector (R) and passes through a
lens (Le) before to go outside.
Apart from B-cells, are present large
cells (A), small cells (C) and D-cells.
On both sides of the lens,
photophore vessels (V) and nerves (N)
enter the organ. Capillaries branch
off from the arteries and pass both
D- and C-cells before they reach the
lantern.
Nerves follow the capillaries and end
at a sphincter-like structure at the
base of the C-cells. Modified from Herring and
Locket (Herring and Locket, 1978) with permission.
The function of these organs include
mating, social interaction or
orientation and a form of counterillumination camouflage against
overhead ambient light
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Bathypelagic fish are black, or
sometimes red, with few photophores.
When photophores are used, it is
usually to entice prey or attract a mate.
Flashlike fish have a retroflector behind
the retina which they use with
photophores to detect eyeshine in
other fish.
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also known as Pyrrhophyta, "fire plants". Some produce
bioluminescence.
Agitation of seawater containing dinoflagellates will stimulate light
flashes.
When the cell is disturbed by a
grazing predator, such as a copepod
(the burglar), it gives a light flash
(the alarm)
which lasts 0.1 to 0.5 sec.
The flash attracts a secondary
predator, such as a small fish
(the police), which closes
in looking for food.
When the copepod sees
the luminescent flash it gives a jump,
because staying put means it is
vulnerable to predation.
Dinoflagellate luciferin is thought to be derived from Chlorophyll, and has a
very similar structure. In Gonyaulax, at pH 8 the molecule is "protected" from
the luciferase by a "luciferin-binding protein", but when the pH lowers to 6, the
luciferin reacts and light is produced.
The production of light is due to
the association of luciferine with a
protein, luciferase, a catalyst.
In the process of being oxidized,
luciferin briefly exists in an excited
state, after which it decays to its
ground state, releasing energy in
the form of photons (light).
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Dinoflagellates are the most common sources of bioluminescence in
the surface waters of the ocean. The light displays created by
breaking waves, swimming fish, or boats are mainly due to
dinoflagellates.
the λ of emission is approximately in the blue-green region of the
visible spectrum.
In most dinoflagellates the bioluminescence is controlled by an
internal clock. At the end of the day the luminescent chemicals are
packaged in vesicles (scintillons), which then migrate into the
cytoplasm. An action-potential is generated in the internal vescicle
membrane. It propagates throughout the cell allowing protons to
pass from the vacuole into the cytoplasm. The cytoplasm is
acidified, and the chemiluminescence is activated in the scintillons.
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Many jellyfish have bioluminescence, especially comb jellies, where
more than 90% of planktonic species are known to produce light.
Arguably, the most famous of all bioluminescent invertebrates is
Aequorea victoria, which is the first species from which GFP (Green
Fluorescent Protein) was isolated, a discovery which went on to win
the Nobel prize.
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Aequoraea victoria produces flashes of blue
light by a quick release of Ca2+ which
interacts with the photoprotein aequorin.
The blue light is in turn transduced to green
by the GFP. Both aequorin and GFP are
important in biological research.
In 1961, Shimomura and Johnson isolated
the aequorin, and its small molecule cofactor,
coelenterazine, from large numbers
of Aequorea jellyfish at Friday Harbor Laboratories.
In 1967, Ridgeway and Ashley microinjected aequorin into
single muscle fibers of barnacles, and observed transient
Ca ion-dependent signals during muscle contraction.
For his research into GFP, Osamu Shimomura was
awarded the 2008 Nobel Prize for chemistry.
Ostracoda
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Bioluminescence is a form of
intraspecific communication
between animals, and can be used
also for defense, and offense.
Many animals use
bioluminescence in multiple ways.
The different ways in which
jellyfish use bioluminescence are
still being discovered.