Biology Reference
In-Depth Information
iii)
Factors Affecting biosynthesis of nodularins
:
High light intensity (105-155 µmol
-2
S
-1
), salinity (15%),
phosphate concentration (1700-5500 µg L
-1
) and temperature (19ºC) supported increased formation of
nodularin in
No
.
spumigena
with prolonged period of incubation (Lehtimaeki
et al
., 1997). Extracellular
nodularin concentration increased with period of incubation suggesting that cell lysis caused
the release of the toxin. A comparative study in batch (phosphate 55-5,500 µg L
-1
; nitrate 100-30,000
µg L
-1
) and chemostat cultures (phosphate 5-315 µg L
-1
) of
Nodularia
strain GR8b revealed that
nodularin content per dry weight, nodularin to protein ratio and extracellular nodularin were
highest after 25 days period but were not infl uenced by the nutrient concentration (Repka
et al
.,
2001). Nodularin concentration per cell was constant under different concentrations of nutrients.
C) Cylindrospermopsin (CYN):
CYN is mainly produced by
Cylindrospermopsis raciborskii
.
Besides CYN,
C
.
raciborskii
is also known to produce saxitoxins, anatoxin-a and PSPs. The genus
Cylindrospermopsis
was created by separating a species of
Anabaenopsis raciborskii
on the basis of
presence of gas vacuoles and pattern of heterocyst differentiation (Seenayya and Subba Raju, 1972)
that has been supported by other workers (Horecka and Komarek, 1979; Hindak, 1988). So far eight
species of
Cylindrospermopsis,
i.e.
C
.
africana
,
C
.
cuspis
,
C
.
philippinensis
and
C
.
raciborskii
from Africa
(Komárek and Kling, 1991);
C
.
allantoidispora
,
C
.
catemaco
,
C
.
tavernae
from Brazil (Komarkova,
1988; Komarkova
et al
., 1999) and
C
.
curvispora
from Japan (Watanabe, 1995) have been described.
Except the last mentioned species, the rest of them do not differentiate akinetes. Of the remaining
seven species,
C
.
raciborskii
is the most frequently reported species and is known to produce the
hepatotoxic alkaloid CYN. The occurrence of
C
.
raciborskii
in Waikato lakes of New Zealand has
been reported (Ryan
et al
., 2003). In Australia,
C
.
raciborskii
was responsible for Palm Island mystery
disease (Byth, 1980; Bourke
et al
., 1983). The only toxin produced by Australian strains is CYN and
its hepatotoxicity has been subsequently established (Hawkins
et al
., 1985; Hayman, 1992; Ohtani
et
al
., 1992; Saker
et al
., 1999).
C
.
raciborskii
does not form typically surface blooms. Maximum densities
of
C
.
raciborskii
occur at 2-3 m below the surface of waters. Secondly, taste and odour problems are
not associated with blooms of
C
.
raciborskii
as it does not produce volatile organic compounds such
as geosmin that is commonly associated with HABs (Saker and Griffi ths, 2001).
Other fi lamentous
cyanobacteria that are reported to produce CYN are
Anabaena
lapponica
from boreal environments
(Spoof
et al
., 2006),
Aphanizomenon
ovalisporum
(Fig. 2 E; Banker
et al
., 1997),
Aph
.
fl os-aquae
(Preussel
et al
., 2006),
Lyngbya wollei
(Fig. 5 A, B; Seifert
et al
., 2007), strains of
Oscillatoria
(PCC 6407, PCC 6506,
PCC 6602, PCC 7926 and PCC 10702; Mazmouz
et al
., 2010),
Raphidiopsis curvata
(Fig. 4 B; Li
et al
.,
2001) and
Umezakia natans
(Harada
et al
., 1994).
i) Structure
:
CYN is a sulfate ester of tricyclic guanidine (mol. wt. 415D) substituted with a
hydroxymethyl uracil (Fig. 10; Ohtani
et al
., 1992). It is a stable compound that is not removed by
boiling (Norris
et al
., 1999). As compared to MCs and nodularins, CYN acts slowly but it exerts its
effects on a number body parts, e.g. kidneys, intestines, lungs though liver is the main organ affected
(Hawkins
et al
., 1985; Terao
et al
., 1994; Falconer
et al
., 1999; Seawright
et al
., 1999; Shaw
et al
., 2000).
Besides CYN,
Cylindrospermopsis
is known to produce STX, a type of paralytic shellfi sh-poisoning
toxins (Lagos
et al
., 1999). CYN-producing cyanobacteria have now been detected in many European,
Central Asian and American water bodies (Falconer, 2005).
Several analogues of CYN have been identifi ed including those of 7-epi-CYN and deoxy-CYN.
The toxicity of CYN has been largely due to the pyrimidine ring, the presence of a hydroxyl group
on the uracil bridge and the ketoenol status of uracil (Mazur-Marzec, 2006). The LD
50
(i.p. for 5 days;
estimated by mouse bioassay) value of 7-epi-CYN of
Aph
.
ovalisporum
has been found to be 200 µg
kg
-1
body weight, a value that is similar to CYN. Its subsequent treatment with chlorine solution