Biology Reference
In-Depth Information
The existence of
O
.
spongeliae
in the tropical marine sponge
L
.
herbacea
has been identifi ed on the
basis of fl ow cytometry separation of the cyanobiont from sponge cells. The role of the cyanobiont
in the production of polychlorinated compounds has also been emphasized. Thus this constitutes
the fi rst report on the production of secondary metabolites by a cyanobiont from sponges. Faulkner
et al
. (1994) separated cells of sponge
L
.
herbacea
and its symbiont
O
.
spongeliae
on the basis of
fl uorescence using a cell sorter (Becton-Dickson FAC Star Plus) to obtain 10 million non-fl uorescent
sponge cells and 2 million fl uorescent cyanobacterial fi laments and showed by NMR spectroscopy
that the cyanobacterial fraction is associated with signals due to 13-demethylisodysidenin as the
major chlorinated metabolite. On the other hand, the sponge cell fraction unambiguously showed
sesquiterpenes herbadysidolide and spirodysin by GC-MS analysis. Similarly, the presence of
2-(2',4'-dibromophenyl)-4,6-dibromophenol as the major metabolite of
L
.
herbacea
(from a shallow
lagoon near Hotel Nikko in Palau) up to 6% dry weight originated from the cyanobiont. This was
confi rmed by fl ow cytometry and NMR spectroscopy that the metabolite was from the fraction of
cyanobacterial symbiont. It was further suggested that these compounds serve the role of chemical
defense of the sponge against predators and bacterial invasion.
II. ECHIUROID WORMS
Two worms,
Ikedosoma gogoshimense
and
Bonellia fuliginosa
that grow in the muddy sand at low tide
levels and coral reefs, respectively possess cyanobionts in their subepidermal connective tissues. No
details of their nature, type of symbionts and their interaction are known (Carpenter, 2002).
III. CORALS
Lesser
et al
. (2004) identifi ed unicellular, symbiotic cyanobacteria in the host cells of the coral
Montastraea cavernosa
collected from the Caribbean Islands. These authors suggest that the cyanobionts
coexist with symbiotic dinofl agellates (zooxanthellae) of the coral and form long term association
within the host cells.
IV. ASCIDIANS
These are classifi ed as Chordates as their larvae possess a notochord. These live as permanently
attached or buried in the sand or mud. In the family Didemnidae of ascidians, fi ve genera form
symbiotic association with two cyanobionts
Synechocystis
and
Prochloron
.
The presence of photosynthetic organisms and the ability of ascidians to evolve oxygen can
be dated back to 1935. Initially identifi ed as
Synechocystis didemni
, it was later named as
Prochloron
didemni
(Lewin, 1975; Newcomb and Pugh, 1975).
P
.
didemni
is characteristic in being a prokaryote
that possesses chlorophyll
a
and
b
but lacks phycobiliproteins (Lewin and Withers, 1975). Chlorophyll
b
is present in a bound form to a protein that differs from Cab protein of plastids of green algae
and higher plants (La Roche
et al
., 1996). The 16S rRNA sequencing revealed closer resemblances to
cyanobacterial lineages. The understanding of microenvironment of
P
.
didemni
in ascidians remained
incomplete and attempts to cultivate the symbiont have not been successful despite unconfi rmed
reports that exist in literature (Kühl and Larkum, 2002).
The cells of
Prochloron
reside in cloacae or embedded in the folds of gelatinous matrix extracellular
to the host that forms a transparent upper tunic/test (Lewin and Cheng, 1989; Hirose
et al
., 1996,
1998). Alberte (1987) reported that up to 60% of carbon demand of ascidians is met by the transfer
