CYANOBACTERIAL TOXINS - Cyanobacteria - page 510

P content under P-limitation. Both carbon fi xation and the rate at which MC was produced in cells
were higher at lower µ. Under P-limited conditions MC-LR was the dominant form produced (Oh et
al ., 2000). On the other hand, N-limited continuous cultures of M . aeruginosa NASH 01-A19 exhibited
a positive linear relationship between MC content per cell, protein, chlorophyll a , cell dry weight and
cell volume. MC content of fast growing smaller cells was higher than in slow growing cells (Long
et al ., 2001). Rapala et al . (1997) found that the toxin content in the cells of Anabaena sp. strain 90 and
202A1 increased with phosphate concentration in medium while at high temperature (25 to 30ºC)
and light intensities (2 to 100 µ mol m -2 s -1 ) the toxin content decreased. Moreover, the production
of different variants of MC varied with growth stimuli where MC-LR was shown to be associated
with temperatures below 25ºC whereas MC-RR was produced at higher temperature (35ºC).
Variations in nitrogen and phosphorus concentrations infl uenced the MC production in
Microcystis strains (Vézie et al ., 2002). Growth rates of Microcystis sp. (Utkilen and Gjolme, 1995;
Rapala and Sivonen, 1998; Kotak et al ., 2000; Oh et al ., 2000) and MC content of M . aeruginosa are
directly proportional to the phosphorus concentration (Jacoby et al ., 2000; Kotak et al ., 2000). On the
other hand, a variation in MC content of M . aeruginosa was suggested to be in relation to N:P ratio
and growth phase (Liu et al ., 2000). Nutrient (nitrogen, phosphorus or iron) and light limitation
infl uence the energetic state of the cyanobacterial cells by causing a stress condition and eventually
affect protein synthesis of the cells but not the synthesis of MC (Bickel and Lyck, 2001). A comparison
of growth in different media revealed that A . fl os-aquae UTEX 2383 supported maximum growth
in terms of cell number, chlorophyll a content and specifi c growth rate along with toxicity of the
cultures in a mouse bioassay (Gupta et al ., 2002).
B) Nodularins: No . spumigena was the fi rst cyanobacterium that has been reported to be toxic to
livestock (Francis, 1878). As a matter of fact nodularin was for the fi rst time isolated from a species
of Anabaena that was known to produce both MCs and nodularins (Carmichael, 1986, 1988). Toxic
Nodularia spp. have been recorded from Germany (Kalbe and Tiess, 1964; Gussmann et al ., 1985),
Denmark (Lindstrom, 1976), Australia (Main et al ., 1977), Finland (Persson et al ., 1984; Eriksson et
al ., 1988) and Sweden (Edler et al ., 1985).
i) Structure : The structure of nodularin was for the fi rst time elucidated by Rinehart et al. (1988) who
suggested that the amino acid composition of the pentapeptide is β-methylaspartic acid, glutamic acid,
arginine, dehydrobutyric acid and Adda (Fig. 9). It is cyclo (-D-MeAsp 1 -L-Arg 2 -Adda 3 -D-Glu 4 -Mdhb 5 ).
The molecular formula of nodularin is C 41 H 6 N 8 O 10 . It has a molecular weight of 824D (Rinehart et
al ., 1988; Eriksson et al ., 1988; Runnegar et al ., 1988; Carmichael, 1988; Duy et al ., 2000). Because of
the presence of Adda in its structure, nodularins possess the same toxicity as of MCs and cause liver
damage leading to death of human beings. Nodularins possess carcinogenic activity (not shown by
MCs) but both are found to be potent tumor promoters (Humpage et al ., 2000; Saker et al ., 2003).
An analogue of nodularin known as motuporin, found in the marine sponge Theonella swinhoei ,
differs from nodularin only by one amino acid. It possesses hydrophobic L-Val in place of L-Arg
in nodularin (de Silva et al ., 1992). Namikoshi et al . (1994) described variants of nodularin where
[DMAdda 3 ]-nodularin, [6(z)-Adda 3 ]-nodularin was found in natural sample while [d-Asp 1 ]-nodularin
was detected in cultures. [L-Har 2 ]-nodularin was produced by a freshwater non-gas vacuolate strain
of Nodularia PCC 7804 (Beattie et al ., 2000; Saito et al ., 2001). Mazur-Marzec et al . (2006) characterized
eight nodularin variants. Besides the unmodifi ed nodularin with an arginine residue (Nod-R), three
variants are demethylated at different sites, i.e. on aspartic acid [D-Asp 1 ]-nodularin, the Adda residue
[DMAdda 3 ]-nodularin and dehydrobutyric acid [dhb 5 ]-nodularin. Two other nodularin variants
have an additional methyl group located in the Adda [MeAdda]-nodularin and Glu [Glu 4 (Ome]-