Cyanobacterial Toxins

<p>Lethal intoxications of animals dwelling in aquatic habitats are recurrently observed with blooms of cyanobacteria. The latter produces two types of toxins : cytotoxins & biotoxins and a few antibiotics (allelopaths) such as acutiphycins, indolcarbazoles, tantazoles, tolytoxins etc. </p><p>Cytotoxins reveal a large spectrum of bustle against bacteria, fungi, algae and mammalian cell lines whereas biotoxins commonly produce intoxications in animals and human beings. Two different kinds of biotoxins produced by cyanobacteria have been examined : neurotoxins and hepatotoxins. It was observed that blooms of algae emanating hepatotoxins are almost twice as common as neurotoxic ones.</p><p>Statistical relations were frequent between hepatotoxicity and occurrence of <em>Microcystis aeruginosa, M. viridis, M. wesenbergii, Anabaena flos-aquae</em> and <em>A. spiroides</em>. Hepatotoxins mostly target liver in mice where they form marked clogging and necrosis in the parenchymal cells around the central vein. Their LD50 values were found between 140 to 160 µg/kg bw.</p><p>Neurotoxicity was, by and large, associated with abundance of certain species of the genera <em>Anabaena, Aphanizomenon, Oscillatoria </em>and<em> Trichodesmium.</em> Of these neurotoxins, saxitoxin (STX) and neosaxitoxin, also termed as 'aphantoxins' are produced by <em>Aphanizomenon flos-aquae. </em>Anatoxin-a (ANTX-a) is an alkaloid neurotoxin produced by <em>Anabaena flos-aquae, A. spiroides and Oscillatoria. </em>The LD50 in mice is about 200 µg/kg body weight as against 10 µg/kg dosages of aphantoxins. Mice injected intraperitoneally with lethal doses of ANTX-a die from respiratory arrest within some minutes showing symptoms like muscle fasciculation, heavy abdominal breath, cyanosis, convulsions and collapse.</p><p>Another neurotoxin - Anatoxin-a(s) {ANTX-a(s)} has similar characteristics to an organophosphate insecticide, being a potent inhibitor of cholinesterase. On treatment with 20 µg/kg bw of dosage (LD50) animals show marked salivation, mucoid nasal emancipation, ataxia, diarrhea, dyspnea and cyanosis. Anatoxin-b (ANTX-b), a neurotoxin with acetocholinesterase activity; is more toxic than anatoxin-a and a(s). However, its exact nature and pharmacological action have yet to be worked out.