Biodiversity of cyanobacteria in Tunisian freshwater reservoirs: occurrence and potent toxicity – a review Afef Fathalli, Mohamed S. Romdhane, Vitor Vasconcelos and Amel Ben Rejeb Jenhani ABSTRACT In spite of the great environmental and sanitary importance of cyanobacteria, their biodiversity is little known in Tunisia. In this work, a review was carried out, based on literature data, of potentially toxic cyanobacteria occurrence in Tunisia. Microcystis, one of the most widely distributed toxic bloom-forming cyanobacteria genera, was represented by Microcytis wesenbergii, found only in Lebna water reservoir, and Microcytis aeruginosa recorded in different water bodies. The invasive potentially toxic cyanobacterium Cylindrospermopsis raciborskii, reported for the first time in Tunisia in October 2004, was observed in the semi-arid to arid areas. The harmful genus Planktothrix was represented in Tunisian freshwater by the green-pigmented species P. agardhii. The filamentous cyanobacteria dominance is increasingly reported in Tunisia in eutrophic water bodies. This dominance increases especially during the summer–autumn period. Recently, potentially toxic cyanobacteria blooms have been reported in some reservoirs in the north east of the country. These blooms were generated by the potentially toxic Chroococcale Microcystis aeruginosa. Harmful cyanobacteria tend to spatio-temporal expansion in the Tunisian inland waters. The toxicological potential evaluated by several methods showed that none of the Tunisian strains were proved to be cylindrospermopsin nor saxitoxin producers. However, the majority of Microcystis were able to synthesize microcystin. Afef Fathalli (correspoding author) Mohamed S. Romdhane Amel Ben Rejeb Jenhani Unité de Recherche Ecosystèmes et Ressources Aquatiques, Institut National Agronomique de Tunisie, 43, Avenue Charles-Nicolle, 1082 Tunis Mahrajène, Tunisia E-mail: fathalli_afef@yahoo.fr Afef Fathalli Institut National des Sciences et Technologie de la Mer, Port de pèche-2060 La Goulette, Tunis, Tunisia Vitor Vasconcelos Centro de Investigação Marinha e Ambiental- CIIMAR/CIMAR, Universidade do Porto, Rua dos Bragas, 289, 4050–123 Porto, Portugal and Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169–007 Porto, Portugal Key words | cyanobacteria, cyanotoxins, genetic variability, Tunisian freshwaters INTRODUCTION Cyanobacteria are a major group of prokaryotes that occur throughout the world (WHO ). They are the Earth’s oldest known oxygen-producing organisms, with fossil remains dating back 3500 million years (Schopf ). Through their photosynthetic activity, they were largely responsible for the modern-day oxygen-enriched atmosphere, and subsequent evolution of our planet’s higher plant and animal life (Schopf ; Whitton & Potts ). Cyanobac- teria have many unique features among phytoplankton, such as buoyancy and nitrogen fixation, and the production of a wide variety of bioactive compounds. Several species of cyanobacteria form blooms that are frequently toxic, and thus pose a health risk for humans and animals (Sivonen & Jones ). They can produce toxic secondary metabolites including hepatotoxins that have carcinogenic potential, neu- rotoxins and lipopolysaccaride endotoxins (Carmichael & Falconer ; Codd ; Carmichael ). The tragic deaths of 70 of 131 patients exposed to the hepatotoxins microcystins (MC) through renal dialysis in Brazil are the only well known substantiated human fatalities due to cyano- toxins ( Jochimsen et al. ). Nevertheless, some illnesses reported previously were life-threatening (Ressom et al. ), such as the poisoning of 138 children and 10 adults due to hepatotoxin cylindrospermopsin (CYN) in Palm Island (Australia) (Hawkins et al. ). While cyanobacterial harmful algal blooms have been reported in the scientific literature for more than 130 years (Francis ), in recent decades, the incidence and intensity 755 © IWA Publishing 2015 Journal of Water Supply: Research and Technology—AQUA | 64.6 | 2015 doi: 10.2166/aqua.2015.119 Downloaded from https://iwaponline.com/aqua/article-pdf/64/6/755/399383/jws0640755.pdf by guest on 05 July 2020