Planktothrix rubescens is a filamentous cyanobacteria (a.k.a blue-green algae) commonly observed in mesotrophic lakes of the Northern Hemisphere1. Like all cyanobacteria, Planktothrix rubescens is a photosynthetic organism, meaning that it captures sunlight for energy using pigments, especially chlorophyll a. Planktothrix rubescens also posses red pigments called phycoerythrin, which give the cells their characteristic color. Even though cyanobacteria are microscopic organisms, they can accumulate and form scums along downwind shores that can be seen by the naked eye. Such mass developments of phytoplankton is named “algal bloom”.
Planktothrix rubescens produces the potent toxins microcystins that are known to bioaccumulate in aquatic vertebrates and invertebrates, including fish, mussels and zooplankton. Poisoning of animals and humans can occur directly through consumption of toxic cyanobacterial cells or indirectly through consumption of contaminated aquatic organisms. In Lake Zurich, P. rubescens represents the dominant organism of the phytoplankton community2. Lake Zurich is a very popular leisure area and is the major source of drinking water for the city of Zurich. The threat posed by microcystins into recreational and drinking waters has obvious and far-reaching implications for public health and the environment3.
A recent study4 by our colleague Thomas Posh evidenced that P. rubescens populations in Lake Zurich have shown no reduction during the last decades, but rather increased due to the warming of the lake water caused by the global climate change. For more details, read the press release of the University of Zurich: Global warming harms lakes.
In freshwater ecosystems, genetic mutations in P. rubescens occur frequently within the gene cluster that code for the mycrocystin production5. Mutations results in strains that do not produce microcystins, but these strains may produce other toxic compounds. Strains that produce microcystin cannot be distinguish from non-producing strains under the microscope, so the discrimination is made using molecular biology approaches on the microcystine gene cluster.
Our goal is to use such molecular techniques (especially the quantitive PCR) to study the factors that regulate the ecological success of microcystin-producing vs. non-producing strains of P. rubescens. These factors are not known, but are thought to be temperature, light condition and/or nutrients levels in the lake. Our study will also help to understand the biological function of the mycrocystins. Ultimately, our molecular methods will provide essential tools for the early warning of toxic bloom formation in natural waterbodies and drinking water reservoirs.
Sivonen, K., and G. Jones. 1999. Cyanobacterial toxins, p. 41–111. In: I. Chorus and J. Bertram (ed.), Toxic cyanobacteria in water: a guide to public health significance, monitoring and management. E&FN Spon, London. ↩
Van den Wyngaert S, Salcher MM, Pernthaler J, Zeder M, Posch T (2011) Quantitative dominance of seasonally persistent filamentous cyanobacteria Planktothrix rubescens in the microbial assemblages of a temperate lake. Limnology and Oceanography 56:97-109. ↩
Funari, E., and E. Testai. 2008. Human health risk assessment related to cyanotoxins exposure. Critical Reviews in Toxicology 38:97–125 ↩
Posch, T., O. Köster, M. M. Salcher, and J. Pernthaler. 2012. Harmful filamentous cyanobacteria favoured by reduced water turnover with lake warming. Nature Climate Change. doi:10.1038/nclimate1581. ↩
Christiansen, G., R. Kurmayer, Q. Liu, and T. Börner. 2006. Transposons inactivate biosynthesis of the nonribosomal peptide microcystin in naturally occurring Planktothrix spp. Applied and Environmental Microbiology 72:117-123 ↩