Cyanophage Distribution Across European Lakes of the Temperate-Humid Continental Climate Zone Assessed Using PCR-Based Genetic Markers.

Studies of the diversity and distribution of freshwater cyanophages are generally limited to the small geographical areas, in many cases including only one or few lakes. Data from dozens of various lakes distributed at a larger distance are necessary to understand their spatial distribution and sensitivity to biotic and abiotic factors. Thus, the objective of this study was to analyze the diversity and distribution of cyanophages within the infected cells using marker genes (psbA, nblA, and g91) in 21 Polish and Lithuanian lakes. Physicochemical factors that might be related to them were also analyzed. The results demonstrated that genetic markers representing cyanophages were observed in most lakes studied. The frequently detected gene was psbA with 88% of cyanophage-positive samples, while nblA and g91 were found in approximately 50% of lakes. The DNA sequence analyses for each gene demonstrated low variability between them, although the psbA sequences branched within the larger cluster of marine Synechoccocuss counterparts. The principal component analysis allowed to identify significant variation between the lakes that presented high and low cyanobacterial biomass. The lakes with high cyanobacterial biomass were further separated by country and the different diversity of cyanobacteria species, particularly Planktothrix agardhii, was dominant in the Polish lakes and Planktolyngbya limnetica in the Lithuanian lakes. The total phosphorous and the presence of cyanophage genes psbA and nblA were the most important factors that allowed differentiation for the Polish lakes, while the pH and the genes g91 and nblA for the Lithuanian lakes.

Role of environmental factors and toxic genotypes in the regulation of microcystins-producing cyanobacterial blooms.

The aim of this study was to understand: (1) how environmental conditions can contribute to formation of Microcystis-dominated blooms in lowland, dam reservoirs in temperate climate-with the use of quantitative molecular monitoring, and (2) what is the role of toxic Microcystis genotypes in the bloom functioning. Monitoring of the Sulejow Reservoir in 2009 and 2010 in two sites Tresta (TR) and Bronislawow BR), which have different morphometry, showed that physicochemical conditions were always favorable for cyanobacterial bloom formation. In 2009, the average biomass of cyanobacteria reached 13 mg L(-1) (TR) and 8 mg L(-1) (BR), and in the second year, it decreased to approximately 1 mg L(-1) (TR and BR). In turns, the mean number of toxic Microcystis genotypes in the total Microcystis reached 1% in 2009, both in TR and BR, and in 2010, the number increased to 70% in TR and 14 % in BR. Despite significant differences in the biomass of cyanobacteria in 2009 and 2010, the mean microcystins (MCs) concentration and toxicity stayed at a similar level of approximately 1 µg L(-1). Statistical analysis indicated that water retention time was a factor that provided a significant difference between the two monitoring seasons and was considered a driver of the changes occurring in the Sulejow Reservoir. Hydrologic differences, which occurred between two studied years due to heavy flooding in Poland in 2010, influenced the decrease in number of Microcystis biomass by causing water disturbances and by lowering water temperature. Statistical analysis showed that Microcystis aeruginosa biomass and 16S rRNA gene copy number representing Microcystis genotypes in both years of monitoring could be predicted on the basis of total and dissolved phosphorus concentrations and water temperature. In present study, the number of mcyA gene copies representing toxic Microcystis genotypes could be predicted based on the biomass of M. aeruginosa. Moreover, MCs toxicity and concentration could be predicted on the basic of mcyA gene copy number and M. aeruginosa (biomass, 16S rRNA), respectively. Present findings may indicate that Microcystis can regulate the number of toxic genotypes, and in this way adjust the whole bloom to be able to produce MCs at the level which is necessary for its maintenance in the Sulejow Reservoir under stressful hydrological conditions.