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
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