Biology Reference
In-Depth Information
there are 11 genes common (
cyrA
to
cyrK
) interspersed with three others like
Orf1
(that encodes an
ATP-grasp protein) and
trp1
and
trp2
(that encode transposases) in
Oscillatoria
PCC 6506. The
cyrL
to
cyrO
genes are not represented in the
cyr
gene cluster of
Oscillatoria
PCC 6506. The
Oscillatoria
PCC 6506
cyrA
,
cyrB
and
cyrC
gene products exhibited a high degree of sequence similarity with
the gene products of
aoaA
,
aoaB
and
aoaC
of
Aph
.
ovalisporum
. Determination of the species of CYN
produced by
Oscillatoria
PCC 6506 during biosynthesis led to the identifi cation of 7-epi-CYN (68.6%)
followed by CYN (30.2%) and traces of 7-deoxy-CYN (Mazmouz
et al
., 2010).
iii)
CYN toxicity
:
As the total chemical synthesis has been achieved (Xie
et al
., 2000), it is possible
to test the analogues for determining the specifi c chemical groups responsible for transport and
toxicity of CYN. Accordingly, Runnegar
et al
. (2002) tested the analogues CYN-DIOL (synthetic CYN
lacking sulfate group) and the derivative of C7 epimer of CYN, EPI-DIOL (having H in place of OH
at position 7) for transport and toxicity. Both these substances exhibited no difference in uptake and
toxicity suggesting that neither sulphate group nor hydroxyl group in 7-epi-CYN contributes to the
toxicity of CYN. Further, the synthesis of 7-deoxy-CYN was achieved and it was suggested that C7
oxygenation was not required for the inhibition of protein synthesis (Looper
et al
., 2005).
iv) Genetic diversity of CYN producers
:
Saker
et al
. (1999) described two morphological types of
C
.
raciborskii,
i.e. straight and coiled trichomes which exhibited CYN content ranging from 0.14 to
0.2%. Special morphological features of
C
.
raciborskii
in batch and continuous cultures (Shafi k
et al
.,
2003) and the morphological changes that occur in bloom development were reported (Padisak,
2003). Sixteen strains of
Cylindrospermopsis
isolated from freshwater bodies (lakes and reservoirs)
in Africa, America, Australia and Europe were subjected to 16S tRNA-23S rRNA ITS region. These
strains are thus grouped into three clusters, i.e. (i) American strains, (ii) strains of Europe and (iii)
African and Australian strains (Gugger
et al
., 2005). A recent colonization of Australian waters by
African strains could be a possible event.
Of the seven strains of
C
.
raciborskii
isolated from Australia, only fi ve of them (CR1, CR2, CR3, CR4
and CR5) produced detectable levels of CYN in their cells in batch cultures. No correlation between
the morphological type (straight or coiled trichomes) and toxin production could be observed. The
addition of nitrate or ammonium compounds to medium did not increase the content of CYN but
the strains responded more positively for CYN production in a growth medium without nitrogen
sources (Saker and Neilan, 2001).
The occurrence of
C
.
raciborskii
from a Canadian mesotrophic to eutrophic hardwater lakes
(Constance Lake, Ottowa, Ontario) has been reported (Hamilton
et al
., 2004). Though initially
known from tropical waters (Hawkins
et al
., 1985),
C
.
raciborskii
has now been collected from sub-
tropical and temperate regions of the world. Studies on bloom development in 39 Brazilian tropical
reservoirs located in the semi-arid region of northeastern Brazil revealed that 80% of the total
phytoplankton density was due to
C
.
raciborskii
. Low ammonia concentration, high temperature
and pH values corresponded with high percentage growth of
Cylindrospermopsis
(Bouvy
et al
., 2000).
Bernard
et al.
(2003) presented a comparative account of the toxicity of
C
.
raciborskii
strains collected
from different geographical regions. The Australian strains as also strains from Florida (USA) and
Thailand produced CYN and caused liver damage associated with effects on the kidneys, adrenal
glands, small intestine, lungs, thymus and heart whereas Brazilian isolates produced toxicity
symptoms of STXs. Analysis by liquid chromatography with fl uorescence detection revealed the
presence of saxitoxin (STX), neoSTX and decarbamoyl STX. On the other hand, French isolates of
C
.
raciborskii
though were responsible for symptoms akin to CYN (moderate, multifocal hepatocellular
necrosis combined with disorganization of parenchyma and congestion of inner sinusoid) did not
