Felföldi, T., Duleba, M., Somogyi, B., Vajna, B., Nikolausz, M., Présing, M., Márialigeti, K., Vörös, L. 2011. Diversity and seasonal dynamics of the photoautotrophic picoplankton in Lake Balaton (Hungary). Aquatic Microbial Ecology, 63, 273-287.
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Lake Balaton is the largest shallow lake of Central Europe. This freshwater ecosystem is well-studied, including the investigation of photoautotrophic picoplankton (PPP). Previous studies revealed that picoeukaryotes could reach extremely high abundance in winter, while picocyanobacteria are the predominant picoplankters in warmer periods, similarly to other lakes in the temperate zone. In addition to the commonly used epifluorescence microscopy allowing only the discrimination of phycocyanin-, phycoerythrin-rich picocyanobacteria and picoeukaryotic algae, we applied PCR-based molecular methods to reveal a detailed genetic diversity and seasonal dynamics of PPP for the first time in Lake Balaton. Our results showed that a single integrated pelagic sample may harbor a large number of picocyanobacterial genotypes with previously unidentified groups. Based on the length polymorphism analysis of the phycocyanin operon (containing a non-coding region with variable size), the composition of picocyanobacterial communities showed significant seasonal changes and spatial variation. The relative importance of some detected picocyanobacterial operational taxonomic units was correlated with environmental factors, such as temperature and concentration of available nitrogen forms. The picoeukaryotic algal community of winter PPP was dominated by chlorophytes related to the group Trebouxiophyceae. Results of this study highlight a fine internal structure and dynamics of PPP community in freshwater ecosystems that is usually blurred with the lower resolution of commonly applied epifluorescence microscopy and flow cytometry.

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