Biology Reference
In-Depth Information
exhibited closest similarity to
Cyanobacterium stanieri
followed by
Prochloron
sp. and
Synechocystis
sp. In order to fi nd out the host specifi city of a particular cyanobiont in certain species of sponges
or population of sponges, Thacker and Starnes (2003) subjected the DNA samples of cyanobionts
of
L. (Dysidea) herbacea
1A and 1B and
L
.
granulosa
for amplifi cation and sequence determination
of 16S rDNA. These three sponge species exhibited a high degree of specifi city for a particular
cyanobacterial group emphasizing the probability of coevolution of both the host and cyanobiont.
Usher
et al
. (2004a) studied the distribution and phylogeny of unicellular cyanobacterial symbionts of
selected marine sponges (
A
.
aerophoba
,
I. variabilis
and
P. fi ciformis
) from the Mediterranean, Australia
(four
Chondrilla
species) and
Haliclona
sp. from both the regions by direct 16S rDNA sequencing.
The cyanobionts comprise at least four closely related species of
Synechococcus
that included
A
.
feldmannii
from
P
.
fi ciformis
and
C. nucula
. A hitherto undescribed symbiont of sponges related to
Oscillatoria rosea
has been recorded from
Cymbastela marshae
from Australia. Diverse sponge genera
from the Mediterranean, Indian, Pacifi c and Southern oceans showed the existence of
S
.
spongiarum
.
Four dictyoceratid marine sponges (
L.
herbacea
,
L
.
chlorea
,
Lendenfeldia chondrodes
and
Phyllospongia
papyracea
) from reef sites of Republic of Palau showed the presence of symbionts belonging to
α-proteobacteria group as revealed by 16S rRNA gene analysis (sequences that fi t into
Rhodobacter
sp.)
besides harbouring
O
.
spongeliae
. Interestingly,
L
.
chondrodes
alone showed additionally the presence
of
Synechocystis
sp. in both surface (pinacoderm) and internal mesohyl whereas
O
.
spongeliae
was
restricted to mesohyl. Specifi c location of these cyanobionts was confi rmed by the fl uorescence
in situ
hybridization experiments.
P
.
papyracea
contained signifi cant number of γ-proteobacteria (Ridley
et
al
., 2005). Steindler
et al
. (2005) traced the 16S rRNA phylogeny of sponge-associated cyanobacteria.
The amplifi cation of 16S rRNA was carried out with primers 361F(5'-GAATTTTCCGCAATGGGC-3')
and 1459 R (5'-GGTAAYGACTTCGGGCRT-3'). Most of the sequences matched with species of
Synechococcus
,
Prochlorococcus
and members of Oscillatoriales suggesting their polyphyletic origin
and that these represent multiple independent symbiotic events. Taylor
et al
. (2005) studied the
biogeography of bacteria associated with the marine sponge
Cymbastela concentrica
by using 16S
rDNA-DGGE (denaturing gradient gel electrophoresis). The DGGE banding patterns indicated
different bacterial communities in this sponge from tropical versus temperate Australia. The tropical
forms of
C
.
concentrica
showed the similar cyanobionts reported earlier in
Mycale
hentscheli
from
New Zealand by Webb and Mass (2002).
Wilkinson and Fay (1979) reported fi xation of nitrogen by sponges growing in coral reef of Red
Sea. Only those sponges gave positive acetylene reduction assay (ARA) that harbour cyanobionts
and those that lacked cyanobionts were reported negative for ARA. It is further suggested that these
cyanobionts play an important role in maintaining the nitrogen balance in marine environments
with low available N where the sponges grow. A variety of functions have been attributed to these
symbionts, of which mention may be made of nutrient acquisition and growth of the sponges
(Wilkinson and Vacelet, 1979; Frost and Williamson, 1980; Wilkinson, 1992; Vacelet
et al
., 1995; Hill,
1996), stabilization of sponge skeleton (Rützler, 1985), processing of metabolic waste (Beer and
Ilan, 1998) and secondary metabolite production (Unson
et al
., 1994; Bewley
et al
., 1996; Flowers
et
al
., 1998; Schmidt
et al
., 2000). The secondary metabolites consist of inhibitors of cell division and
various enzymes, that affect multiplication of viruses, fungi and a number of microbes. Some other
secondary metabolites exhibit anti-infl ammatory, antitumor, antiviral properties and toxicity to
cellular and cardiovascular systems (Munro
et al
., 1999; Lee
et al
., 2001). Other functions performed
by these metabolites are predator and competitor deterrence (Pawlik
et al.
, 1995; Thacker
et al.
, 1998;
Engel and Pawlik, 2000) and resistance to malignant microbial infections (Garson, 2001; Thakur
et al.
, 2003).
