| Institution: | 1. Department of Botany and Hydrobiology, The John Paul II Catholic University of Lublin, Konstantynów 1H, 20-708 Lublin, Poland;2. Department of Hydrobiology, University of Life Sciences in Lublin, Dobrzańskiego 37, 20-262 Lublin, Poland;3. Polish Academy of Sciences, Centre for Ecological Research, Experimental Station, Nieca?a 18, 20-080 Lublin, Poland;1. Institut Pasteur, Unité des Cyanobactéries, Centre National de la Recherche Scientifique (CNRS) Unité de Recherche Associée (URA) 2172, 75724 Paris Cedex 15, France;2. Centre d’Analyse Environnementales, Bât. Dufy, 1 place de Turenne, 94417 Saint-Maurice Cedex, France;3. AnagnosTec GmbH, Am Mühlenberg 11, 14476 Potsdam-Golm, Germany;1. Taihu Lake Laboratory Ecosystem Station, State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, PR China;2. University of Chinese Academy of Sciences, Beijing 100049, PR China;1. IMDEA Water Institute, Av. Punto Com, 2, Alcalá de Henares, Madrid, 28805, Spain;2. Departamento de Biología, C. Darwin 2, Universidad Autónoma de Madrid, Cantoblanco, 28049, Spain;1. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P.O. Box 2871, Beijing 100085, China;2. Beijing Climate Change Respond Research and Education Centre, Beijing University of Civil Engineering and Architecture, 1 Zhanlan Rd., Xicheng, Beijing 100044, China;3. Department of Chemistry, University of Oslo, 0315 Oslo, 1033, Norway;4. Department of Biosciences, University of Oslo, 0316 Oslo, 1066, Norway;5. Miyun Reservoir Administration, Xiwenzhuang, Miyun, Beijing 101512, China;1. U.S. Geological Survey, Ohio Water Science Center, 6480 Doubletree Avenue, Columbus, OH 43229, USA;2. U.S. Geological Survey, Kansas Water Science Center, 4821 Quail Crest Place, Lawrence, KS 66049, USA;3. University of Toledo, Lake Erie Center, 6200 Bay Shore Road, Oregon, OH 43616, USA |
| Abstract: | The filamentous cyanobacterium Planktothrix rubescens produces secondary metabolites called microcystins (MC) that are potent toxins for most eukaryotes, including zooplankton grazers, cattle and humans. P. rubescens occurs in many deep and thermally stratified lakes throughout Europe. In Lake Zurich (Switzerland), it re-appeared in the 1970s concomitant with decreasing eutrophication. Since then, P. rubescens has become the dominant species in this major drinking water reservoir, where it forms massive metalimnetic blooms during late summer. These cyanobacteria harbor subpopulations of non-MC producers, but little is known about the environmental factors affecting the success of such genotypes. The non-MC-producing subpopulation of P. rubescens was studied using a quantitative real-time PCR (qPCR) assay on the MC synthetase (mcy) gene cluster that targets a deletion on the mcyH and mcyA genes, which inactivates MC biosynthesis. Two complementary qPCR assays were used to assess the total population abundance (based on the 16S rDNA gene) and the mcy gene copy number (based on a conserved region in the adenylation domain of the mcyB gene). The objective was to evaluate the seasonal patterns of the share of non-MC-producing filaments in the total P. rubescens population. The mcyHA mutants were present in low proportions (up to 14%) throughout the year. Their highest relative abundances occurred during the winter mixis, when total concentrations of P. rubescens were minimal. The MC deficient mutants seemed to better survive in sparse populations, possibly because of lower grazing pressure and a consequently reduced need for MC-mediated protection. Alternatively, the mutants might cope better with the sub-optimal, stressful pressure and light conditions during the winter mixis. Altogether, our results suggest that subtle trade-offs might seasonally determine the proportions of non-MC producers within P. rubescens populations. |
