PHYTOPLANKTON Short research note Isolation of viable cell mass from frozen Microcystis viridis bloom containing microcystin-RR Ga ´bor Vasas • Istva ´n Ba ´csi • Gyula Sura ´nyi • Ma ´rta Miko ´ne ´ Hamvas • Csaba Ma ´the ´ • Sa ´ndor Alex Nagy • Gyo ¨rgy Borbe ´ly Published online: 13 December 2009 Ó Springer Science+Business Media B.V. 2009 Abstract Cyanobacterial species commonly occur in the phytoplankton of freshwater lakes and some- times develop as toxin-producing blooms. Microcys- tis is one of the most common genera of freshwater cyanobacteria and is often the dominating phyto- plankton of eutrophic lakes all over the world. In eutrophic lakes, large amounts of Microcystis may overwinter in the sediment and re-inoculate the water column in spring. In most cases, the overwintering pelagic population—if it exists—is small, and its role in re-inoculation has not been clear yet. In December 2005, we found large amounts of Microcystis on the surface, frozen in the ice cover in a eutrophic pond (Pond Ha ´rmashegy, Hungary). We identified the Microcystis species and investigated the viability and the toxicity of the frozen cells. The dominant species in the bloom samples was Microcystis viridis. Viability tests showed that the colonies isolated from the ice cover were composed of living cells. The isolated strain was found toxic, we analyzed the microcystin composition in the frozen planktonic Microcystis mass; in the investigated samples microcystin-RR was the main cyanotoxin. Keywords Microcystis viridis Á Overwintering Á Pelagic population Á Microcystin-RR Microcystis is one of the most common and wide- spread genus of freshwater cyanobacteria all over the world. In most cases it is the dominant component of phytoplankton in eutrophic lakes (Reynolds et al., 1981). Microcystins are far the best known cyano- toxins that can be isolated from surface water blooms dominated by Microcystis species. They are cyclic heptapeptides known as hepatotoxins, since they cause the illness or even death of animals by damaging the liver (Carmichael, 1992). Later studies showed that cyanobacterial species, different from Microcystis also produce these kinds of metabolites (Brittain et al., 2000; Lyra et al., 2001; Vieira et al., Guest editors: T. Zohary, J. Padisa ´k & L. Naselli-Flores / Phytoplankton in the Physical Environment: Papers from the 15th Workshop of the International Association for Phytoplankton Taxonomy and Ecology (IAP), held at the Ramot Holiday Resort on the Golan Heights, Israel, 23–30 November 2008 G. Vasas (&) Á G. Sura ´nyi Á M. M. Hamvas Á C. Ma ´the ´ Á G. Borbe ´ly Department of Botany, Faculty of Sciences and Technology, University of Debrecen, Egyetem te ´r 1, 4032 Debrecen, Hungary e-mail: vasasg@tigris.unideb.hu S. A. Nagy Department of Hydrobiology, Faculty of Sciences and Technology, University of Debrecen, Egyetem te ´r 1, 4032 Debrecen, Hungary I. Ba ´csi CETOX Analytical and Toxicological, Researching and Consulting Ltd, Egyetem te ´r 1, 4032 Debrecen, Hungary 123 Hydrobiologia (2010) 639:147–151 DOI 10.1007/s10750-009-0025-1