RESUMO
An increased incidence of cyanobacterial blooms, which are largely composed of toxigenic cyanobacteria from the Microcystis genus, leads to a disruption of aquatic ecosystems worldwide. Therefore, a better understanding of the impact of environmental parameters on the development and collapse of blooms is important. The objectives of the present study were as follows: (1) to investigate the presence and identity of Microcystis-specific cyanophages capable of cyanobacterial cell lysis in a lowland dam reservoir in Central Europe; (2) to investigate Microcystis sensitivity to phage infections with regard to toxic genotypes; and (3) to identify key abiotic parameters influencing phage infections during the summer seasons between 2009 and 2013. Sequencing analysis of selected g91 gene amplification products confirmed that the identified cyanophages belonged to the family Myoviridae (95 % homology). Cyanophages and Microcystis hosts, including toxic genotypes, were positively correlated in 4 of the 5 years analyzed (r = 0.67-0.82). The average percentage of infected Microcystis cells varied between 0.1 and 32 %, and no particular sensitivity of the phages to toxigenic genotypes was recorded. The highest number of cyanophages (>10(4) gene copy number per microliter) was observed in the period preceded by the following: an increase of the water retention time, growth of the water temperature, optimum nutrient concentrations, and the predomination of Microcystis bloom.
