MCYST UPTAKE BY THE CLAM M. MACTROIDES Atlântica, Rio Grande, 32(1) 79-85, 2010. doi: 10.5088/atl. 2010.32.1.79 79 MICROCYSTINS UPTAKE BY THE YELLOW CLAM MESODESMA MACTROIDES (BIVALVIA, MACTROIDEA) JANAINA DE CASTRO LEÃO; SHEILA BUENO GIORDANO; JOÃO SARKIS YUNES Universidade Federal do Rio Grande – Instituto de Oceanografia – Unidade de Pesquisa em Cianobactérias – Av. Itália Km 8, Campus Carreiros, Caixa Postal: 474, CEP: 96201-900 -Rio Grande, RS – Brazil 1 jcleao77@yahoo.com.br ABSTRACT Microcystins (MCYST), common cyanobacterial hepatotoxins, have been observed in the Patos Lagoon and the estuary over the last three decades. Anthropogenic pollution associated to the environmental features has promoted the frequent occurrence of cyanobacterial blooms in this environment. The present work aimed to evaluate the MCYST uptake by the filter-feeding mollusk Mesodesma mactroides Deshayes, 1854, which occurs in the nearby coasts of the Patos Lagoon estuary, Brazil. Bioassays were carried out using the toxic strain Microcystis aeruginosa RST9501, isolated from the Patos Lagoon estuary. Clams were exposed to live cells of this toxic cyanobacterium for 12 days, taking up MCYST to a maximum of 5.27±0.23 μg MCYST.g -1 (dry hepatopancreas weight). Since several blooms reaching the Patos Lagoon estuary and the nearby areas are observed, these results indicate that the toxins from M. aeruginosa blooms can be accumulated by this filter-feeding animal, making it a potential vector to the local trophic web. KEY WORDS: Patos Lagoon, Microcystis, microcystin, Mesodesma, bioaccumulation. RESUMO Retenção de microcistinas pelo marisco Mesodesma mactroides (Bivalvia, Mactroidea) As microcistinas (MCYST), hepatotoxinas produzidas por cianobactérias, tem sido encontradas na Lagoa dos Patos e seu estuário ao longo dos últimos trinta anos. A poluição antropogênica associada com as características ambientais locais tem favorecido a ocorrência de florações de cianobactérias nesse ambiente. O presente trabalho teve como objetivo avaliar a assimilação de MCYST pelo molusco filtrador Mesodesma mactroides Deshayes,1854, que ocorre na costa adjacente ao estuário da Lagoa dos Patos, Brasil. Experimentos em laboratório foram realizados utilizando uma cepa tóxica da espécie Microcystis aeruginosa RST9501, isolada do estuário da lagoa dos Patos. Os mariscos foram expostos a células vivas da cianobactéria tóxica durante 12 dias, apresentando um valor máximo de retenção de 5,27±0,23 μg MCYST.g -1 (peso seco do hepatopâncreas). Uma vez que diversas florações contendo M. aeruginosa atingindo o estuário da Lagoa dos Patos e áreas costeiras são observadas, os resultados indicam que essas toxinas, comuns nessas florações, podem ser acumuladas por esse animal filtrador, tornando-o um potencial vetor para a teia trófica local. PALAVRAS CHAVE: Lagoa dos Patos, Microcystis, microcistina, Mesodesma, bioacumulação. INTRODUCTION Microcystins (MCYST), common cyanobacterial hepatotoxins, inhibit protein phosphatases enzymes PP1 and PP2A and induce oxidative stress in different organisms as macrophytes, polychaetes, crab and fish, causing cell damage (Pflugmacher, 2004; Dewes et al., 2006, Pietro et al., 2006, Leão et al., 2008). Anthropogenic pollution has promoted cyanobacterial toxic blooms in water bodies worldwide. Several blooms containing toxic Microcystis aeruginosa cells, able to produce MCYST, have occurred in the Patos Lagoon (Southern Brazil) over the last three decades with effects on the aquatic life. Alterations of biochemical and physiological parameters in several aquatic organisms have been observed (Yunes et al., 1998; Pinho et al., 2005; Rosa et al., 2005; Dewes et al., 2006, Leão et al., 2008). The Patos Lagoon (30 o 20’S to 32 o 10’S) is the second largest inland water body in Brazil and the largest lagoonal complex in South America. Along its margins more than three million inhabitants live in several cities and villages, using its waters as a domestic supply and for leisure, fisheries, agriculture, navigation and as a final recipient of domestic and industrial sewage (Yunes et al., 1998). M. aeruginosa occurs in the Patos Lagoon estuary during all over the year, especially in summer and spring, when blooms are common events. Frequently, cyanobacterial blooms from the Patos Lagoon reach the estuary and the nearby seacoast (Matthiensen et al., 1999). Shellfish can filter large volumes of waters containing toxic substances leading to uptake and accumulation of toxins. Previous studies have observed that cyanotoxins do not cause toxic effects in filter-feeding mollusks, which make them a consumption risk (Vasconcelos, 1995; Christoffersen, 1996; Williams et al., 1997; Amorim e Vasconcelos, 1999). Mesodesma mactroides Deshayes, 1854 is endemic in the Atlantic coast of South America, occuring from Ilha Grande (23 o S, Rio de Janeiro