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Dr. Winfried Behr

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Algal toxins

Algal toxins are a group of strongly toxic substances occuring in the cells of a number of Cyanophyceae (blue-green microalgae). Lysis of the cells allows the release of the substances into the water so that also cell free water can have a toxic effect. Many toxic cyanophyceae, however, develop next to the toxins also substances with an extremely strong odor which functions as a warning so that poisoning of humans is relatively rare (while cattle poisoning is not uncommon). In fresh water the following Algal toxin forming genera occur:  Microcystis, Anabaena, Planktothrix, Nostoc. Aphanizomenon and Cylindrospermopsis. Nodularia is found predominantly in seawater (ZECH, 2001). Algal toxins are either hepatotoxic  (Microcystin, Nodularin) oder nerve toxins (Anatoxin, Saxitoxin). The hepatotoxins are generally cyclic oligopeptides which inhibit protein phosphatases. They may enter liver cells, but not other cell types, which explains their specific liver toxicity. About 100 variants of this class of substances have been identified. All have in common that they contain the rare  C20 amino acid "Adda". The toxicity of the algal nerve toxin is based on the fact that they either funtion as analogon of acetyl cholin (anatoxin-a), as cholin esterase inhibitor (anatoxin-a(S)) or that they block sodium channels (Saxitoxin) (WELLER, 2002).

Publications on algal toxins have caused a concern about potential Algal toxin contamination of  products used among others as supplement food for health reasons. In this context the following has to be considered: Algal toxins occur either in the intact cyanophycea cells or after lysis of the cells in the surounding water. In products of low moisture content a contamination could only be caused by the presence of algal cells.
In case of the cyanophycea Aphanizomenon flos-aquae (blue green alga, Klamath alga) such a contamination can be imagined, although the actual hazard may be insignificant. Aphanizomenon flos aquae is not cultivated but is harvested "from the wild", that is, normally from the Upper Klamath Lake in Oregon. In the phytoplacton of this lake Microcystin (as, however, the only algal toxin) was found, probably caused by the occurrence of Microcystis.
Toxic strains (of Microcystis aeruginosa, Anabaena flos aquae) can often morphologically not be distinguished from the non-toxic ones. However, the former common assumption that Aphanizomenon flos aquae itself has a toxic variant (CARMICHEAL, 1997; MAHMOOD, 1087;  RAPALA, 1993) has recently been questioned (LI, 2000).
At any rate, manufacturers of Aphanizmenon have established an extensive control program (Mouse bioassay, enzyme linked immuno sorbent assay (ELISA) etc) in order to assure that commercial Aphanizomenon flos aquae is free of toxins. In line with a recommendation of the World Health Organization the Department of Agriculture of Oregon has fixed the upper allowable limit of Microcystin to be 1 microgram per gram of algal product. (CHORUS, 1999; CARMICHAEL, 2000).

In another commercially used algal product, Spirulina platensis (actually Arthrospira) Phycotoxins cannot occur for the simple reason that Spirulina grows in an alcaline medium of a pH of around 9 which prevents the growth of other organisms. There are no toxic cyanophyceae known which would survive under such circumstances and analyses of commercial samples of Spirulina have always found to toxin free (KUIPER-GOODMAN, 2001; LAWRENCE, 2001). When methods for the mass culture of micralgae (especially Spirulina, Scenedesmus and Clorella)  were developped a few decades ago much attention was paid to the possibility of occurrence of toxic substances. The following substances were searched for:  Aflatoxin, Ochratoxin A, Sterigmatocystin, Citrinin, Patulin, Penicillins„ure, Zearalenon, T2-Toxin, Diacetoxysciroenol, Trichothecene,  Fumitremorgen and Verucolugen. None of the listed toxins was ever discovered in algal samples, all biological tests had a negative result  (BECKER,1984(I), BECKER 1984(II)).
Also in case of the kelp species Lithothamnium used as Calcium and Magnesium source a Algal toxin contamination can be excluded. The partly fossilized calcareous Lithothamnium leaves are collected from the sea bottom where cyanophyceae never occur in noticeable concentrations (toxic cyanophyceae form rather floating accumulations). Be it only for the difference in size the microscopic cyanophycea cannot by chance be harvested together with Lithothamnium leaves. The same applies also to various other kelp species (as Laminaaria and Fucus) used on account of their Iodine content.


(Questions concerning algal toxins are answered by  Dr. E.W. Becker, Tübingen,
email: wolfgang.becker@med.uni-tuebingen.de)


References


BECKER, E.W.(I), VENKATARAMAN, L.V. 1984: Production and utilization of the blue-green alga Spirulina in India. Biomass, 4, 105-125
BECKER, E.W.(II), 1984: Biotechnology and exploitation of the green alga Scendesmus obliquus in India, Biomass, 1-19
CARMICHAEL, W.W., 1997: The cyanotoxins. In Advances in Botanical Research, Vol. 37 (Ed. by J.A. Callow), pp 211-256. Academic Press, London
CARMICHAEL, W.W.; DRAPEAU, C.; ANDERSON, D.M., 2000: Harvesting of Aphanizomenon flos aquae Ralfs ex Born. & Flah var. flos aquae (Cyanobacteria) from Klamath Lake for human dietary use. Journmal of Applied Phycology, 12, 585-595
CHORUS, i., BARTRAM J. (eds). 1999: Toxic Cyanobacteria in water - A guide to their public health consequences. Monitoring and Management. E & FN Spon, London
KUIPER-GOODMAN, T., et al., 2001: Risk Assessment of microcystins in blue-green algal health food products, in: Mycotoxins and phycotoxins in perspective at the turn of the millenium. Proceedings of the Xth International IUPAC symposium on mycotoxins and phycotoxins 21-25 May, 2000, Guarauja (Brazil), eds. W.J. de Koe, R.A. Samson, H.P. van Egmond, J. Gilbert, M. Sabino, IUPAC and AOAC International, Ponsen and Looyen, Wageningen, The Netherlands, pp. 549-556                                                LAWRENCE, J., et al., 2001: Comparison of Liquid Chromatography/Mass spectrometry, ELISA, and Phosphatase assay for the determination of microcystins in blue-green algae products. J. AOAC Int. vol. 84, no. 4, 1035-1044                                                                                                                                      LI, R.H., CARMICHAEL, W.W., LIU, Y.D., WATANABE, M.M., 2000: Taxonomic re-evaluation of Aphanizomenon flos aquae NH-5 based on morphology and 16S rRNA gene sequences. Hydrobiologia, 438, 99-100
MAHMOOD, N.A. CARMICHEAL, W.W., 1987: Annatoxin-a(s), an anticholinesterase from the cyanobacterium Anabaena flos aquae NRC-525-17. Toxicon, 25, 1221-1227
RAPALA, J.; SIVONEN, K., LYRA, C., NIEMELˇ S.I., 1993: Anatoxin-a concentration in Anabaena and Aphanizomenon flos-aquae at different environmental conditions and comparison of growth by toxic and non-toxic Anabaena strains, a laboratory study.
Applied Environmental Microbiology, 64, 99-105
WELLER, M.G., 2002: Algengifte im Wasser. Nachrichten aus der Chemie, 06/2002, S. 700-7005
ZECH; CH., 2001: Entwicklung von immunanalytischen, chromatographischen und massenspektrometrischen Methoden zur Bestimmung cyanobakterieller Hepatotoxine (Microcystine und Nodularine). Dissertation, TU München, Nov. 2001, S.3
 


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