Absence of evidence for viral infection in colony-embedded cyanobacterial isolates from the Curonian Lagoon

The aim of the present study was to assess the frequency of viral infections in colony-embedded cells of the cyanobacteria Aphanizomenon flos-aquae and Microcystis aeruginosa collected from the brackish Curonian Lagoon. Natural and mitomycin C-treated A. flos-aquae and M. aeruginosa samples were examined for the presence of viruses and lysis by a combination of light-, epifluorescence and transmission electron microscopy techniques. Here we report a lack of evidence for virus infection, progeny formation and cell lysis in colony-embedded cells of A. flos-aquae and M. aeruginosa. These results indicated that viruses contribute little to the mortality of these cyanobacteria when the latter occur in colonies. Consequently, the results supported the hypothesis that colony formation can, at least temporarily, provide an efficient strategy for protection against virus-induced mortality. Finally, assuming that grazing has a negligible effect on colony-embedded cells in the Curonian Lagoon, we propose that most of the cyanobacterial biomass produced is lost from the pelagic food web by sedimentation.