Aphanizomenon toxins

The main genera responsible for freshwater toxic blooms are Microcystis, Anabaena, Aphanizomenon and Oscillatoria. Toxins produced include 1. anatoxins, alkaloids and peptides of Anabaena 2. the peptide microcystin and related peptides of Microcystis 3. aphantoxins, compounds of Aphanizomenon with properties similar to some paralytic shellfish poisons. Properties of Oscillatoria toxin suggest they are peptides similar to those of Microcystis. Microcystis toxins are peptides (M.W. approx. 1200) which contain three invariant D-amino acids, alanine, erythro-3-methyl aspartic and glutamic acids, two variant L-amino acids, N-methyl dehydro alanine and a 3-amino acid. Individual toxic strains have one or more multiples of this peptide toxin. The one anatoxin characterized is a bicylic secondary amine called anatoxin-a (M.W. 165). The aphantoxin isolated in our laboratory contains two main toxic fractions. On TLC and HPLC the fractions have the same characteristics as saxitoxin and neosaxitoxin. 

Two other suspected alkaloid producing cyanobacteria strains, Anabaena flos-aquae NRC-525-17 and Aphanizomenon flos-aquae NH-5, are now being studied. The toxin of flos-aquae NRC-525-17 (anatoxin-a(s)) is thought to have CNS stimulating properties (7) and that of Aph. flos-aquae NH-5 (aphantoxin) is thought to produce the paralytic shellfish poisons saxitoxin and neosaxitoxin (Fig. 1)... 

Cyanobacterial toxins (both marine and freshwater) are functionally and chemically a diverse group of secondary chemicals. They show structure and function similarities to higher plant and algal toxins. Of particular importance to this publication is the production of toxins which appear to be identical with saxitoxin and neosaxitoxin. Since these are the primary toxins involved in cases of paralytic shellfish poisons, these aphantoxins could be a source of PSP standards and the study of their production by Aphanizomenon can provide information on the biosynthesis of PSP s. The cyanobacteria toxins have not received extensive attention since they have fewer vectors by which they come in contact with humans. As freshwater supplies become more eutrophicated and as cyanobacteria are increasingly used as a source of single cell protein toxic cyanobacteria will have increased importance (39). The study of these cyanobacterial toxins can contribute to a better understanding of seafood poisons. 

Cyanobacterial (Blue-Green Bacteria) Toxins. Cyanobacterial poisonings were first recognized in the late 1800s. Human poisonings are rare however, kills of livestock, other mammals, birds, fish, and aquatic invertebrates are common. It is caused by a variety of biotoxins and cytotoxins, including anatoxin, microcystin, and nodularin produced by several species of cyanobacteria, including Anabaena, Aphanizomenon, Nodularia, Oscillatoria, and Microcystis. The main contamination problems include all eutrophic freshwater rivers, lakes, and streams. 

The same toxin has been subsequently isolated from the cyanobacterium Umezakia natans in Japan (Harada 1994) and Aphanizomenon ovalisporum in both Australia (Shaw 1999) and Israel (Banker 1997). An analogue of cylindrospermopsin such as 7-epicylindrospermopsin has been recently characterized as a toxic minor component of a strain of Aph. ovalisporum from Israel (Banker 2000). See Fig. 14.3. 

To date, eylindrospermopsins are only known to be produced by Cylindrospermopsis raciborskii (Hawkins et al, 1985), Aphanizomenon ovalisporum (Banker et al, 2000 Shaw et al, 1999), Umezakia natans (Harada et al, 1994), and Raphidiopsis curvata (Li et al, 2001), mainly in tropical areas. Cylindrospermopsin (CYN) has been identified in New Zealand field extracts, but the toxin-producing cyanobacterium was not identified (Stirling and QuUliam, 2001). 

Ferreira, F.M.B., Soler, J.M.F., Fidalgo, M.L., Femandez-Vila, P. (2001). PSP toxins from Aphanizomenon flos-aquae (cyanobacteria) collected in the Crestuma-Lever reservoir (Douro... 

Ikawa, M., Wegener, K., Foxall, T.L., Sasner, J.J. (1982). Comparison of the toxins of the blue-green alga Aphanizomenon flos-aquae with the Gonyaulax toxins. Toxicon 20 747-52. 

N., Oshima, Y. (2000). Paralytic shellfish toxins in the freshwater cyanobacterium Aphanizomenon flos-aquae, isolated from Montargil reservoir, Portugal. Toxicon 38 1689-1702. 

In aquaculture ponds, fish kills due to toxic cyanobacterial blooms are infrequent, and there is little direct evidence of harmful consequences of toxin-producing cyanobacteria in aquaculture ponds [18]. At least one report [19] attributes large losses of channel catfish (Ictalurus punctatus L.) in a catfish production pond in the southeastern United States to the toxic cyanobacterium Aphanizomenon flos-aquae. Fish may avoid ingesting harmful quantities of toxic cyanobacteria to help reduce the adverse consequences posed by such blooms. In any case, prolonged exposure to toxin-producing cyanobacteria may stress fish and cause them to become more susceptible to adverse conditions, thereby reducing growth [18]. 

Anatoxins are alkaloids produced exclusively by the cyanobacterial genera Anabaena, Planktothrix, and Aphanizomenon. Anatoxin-a (Figure 1C), the first cyanobacterial toxin to be chemically and functionally characterized in 1972, is a secondary amine whose ionization state varies with the pH (pfCa = 9.4). This compound is highly polar and fully soluble in water. Its methylated derivative homoanatoxin-a presents very similar properties. At elevated pH (above 10), both toxins become unstable and degrade very quickly into nontoxic analogs. 

Sawyer PJ, Gentile JH, Sasner JJ Jr (1968) Demonstration of a toxin from Aphanizomenon flos-aquae (L.) Ralfs. Can J Microbiol 14 1199-1204... 

Sasner JJ, Jr., Ikawa M, Foxall TL (1983) Studies on Aphanizomenon and Microcystis toxins. ACS Symposium Series, vol 262, Sea Food Toxins, American Chemical Society, Washington DC, pp 391—406... 

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