1. Group for Aquatic Microbial Ecology, Environmental Microbiology and Biotechnology, University Duisburg-Essen, Essen, Germany
2. Institute for General Microbiology, Christian Albrechts University, Kiel, Germany
3. Essen, Germany
4. Phycology Group, Faculty of Biology, University Duisburg-Essen, Essen, Germany
5. Centre of Water and Environmental Research (ZWU), University of Duisburg-Essen, Essen, Germany