Biology Reference
In-Depth Information
Table 1: contd....
Country
Toxic Species
Cyanotoxin
Authors
Sweden
M
.
aeruginosa
,
M
.
viridis
,
P
.
prolifi ca
,
P
.
agardhii
Microcystins
WHO (2003)
Switzerland
O
.
limosa
Oscillatoria
spp.,
Phormidium
spp.
Microcystins
Hepatotoxins &
neurotoxins
Mez
et al
. (1996)
Mez
et al
. (1997)
M.aeruginosa
Turkey
Microcystins
Albay
et al
. (2005)
USA
A
.
circinalis
Anatoxin-a
Schwimmer and Schwimmer (1964);
Gibson and Smith (1982);
Princep
et al
. (1992); Puschner
et al
.
(1998); Jacoby
et al
. (2000);
Rinkta-Kanto
et al
. (2005); Oberholster
et
al
. (2006)
Microcystins
Hapalosiphon hibernicus
Microcytins
M
.
aeruginosa
I. HEPATOTOXINS
Structurally MC and nodularin are cyclic peptides, the former being a heptapeptide and the latter a
pentapeptide. Both MCs and nodularins possess a unique hydrophobic amino acid known as Adda
(Eriksson
et al
., 1987). The toxicity of MCs and nodularins is due to the presence of Adda chain and
any change in the Adda chain reduces the toxicity of these toxins (Carmichael, 1992; Stotts
et al
., 1993;
Dow and Swoboda, 2000; Duy
et al
., 2000). On the other hand, CYN is a cyclic guanidine alkaloid.
The information on their structure and biosynthesis is presented here.
A) Microcystins:
These are the most widely distributed because a number of cyanobacteria produce
these toxins. MCs are cyclic heptapeptides with a molecular weight ranging from 909 to 1,115 D.
Because initial isolation of this toxin was done from
M
.
aeruginosa
, the toxin was named as microcystin
(Botes
et al
., 1985). Structural analysis of MCs from
M
.
aeruginosa
and
A
.
fl os-aquae
revealed equimolar
amounts of glutamic acid, alanine, arginine and leucine besides β-methylaspartic acid and the
peptides appeared to be cyclic (Krishnamurthy
et al
., 1986). The general structure of MC is cyclo
(D-Ala
1
-L-Xaa
2
-D-erythro-β-methyl-D-iso-Asp
3
-L-Zaa
4
-Adda
5
-D-isoGlu
6
-N-methyldehydro-Ala
7
(Carmichael
et al
., 1988; Krishnamurthy
et al
., 1989). Adda (2S, 3S, 8S, 9S)-3-amino-9-methoxy-2,
6, 8-trimethyl-10 phenyldeca-4-6-dienoic acid) is the novel β-amino acid that is responsible for the
toxicity of MC. The toxin consists of
two protein and fi ve non-protein amino acids. The variability
in the different forms of MCs is due to the variability in the former while the latter appear to be
relatively constant. The fi rst letter code of the variable L-amino acids at position 2 (Xaa) and 4 (Zaa)
is taken to designate the different forms of MCs. The most widely studied variant of MC is MC-LR
with L-leucine and L-arginine at Xaa and Zaa positions (Fig. 6). MC-LR is produced by
M
.
aeruginosa
(Botes
et al
., 1985),
M
.
aeruginosa
UTEX 2388 (Oh
et al
., 2000),
M
.
aeruginosa
strain B 2666 (Diehnelt
et
al.
, 2006),
M
.
viridis
(Watanabe
et al
., 1988),
A
.
fl os
-
aquae
(Rinehart
et al
., 1988; Krishnamurthy
et al
.,
1989; Sivonen
et al
., 1992a),
Anabaena
sp. strain 90,
Anabaena
sp. strain 141 (Sivonen
et al
., 1992a) and
Antarctic cyanobacterial communities (Jungblut
et al
., 2006). Botes
et al
. (1984) characterized MCs
from
M
.
aeruginosa
in which Xaa and Zaa residues identifi ed were L-leucine and L-alanine (MC-
LA) and L-tyrosine and L-methionine (MC-YM), respectively. Three additional forms of MCs have
been identifi ed by Botes
et al.
(1985) that consisted of L-tyrosine at Xaa and variable aminoacids at
Zaa positions i.e., MC-YR(L-tyrosine and L-arginine), MC-YA (L-tyrosine and L-alanine) and MC-
YM(O) (L-tyrosine and methionine S-oxide). MC-YR production by
M
.
viridis
(Watanabe
et al
., 1988)
and
M
.
aeruginosa
UTEX 2388 (Oh
et al
., 2000) has also been reported subsequently. Gathercole and