Cyanobacterial cytoskeleton immunostaining: the detection of cyanobacterial cell lysis induced by planktopeptin BL1125 BOJAN SEDMAK1*, SHMUEL CARMELI2, MARUŠA POMPE-NOVAK3, MAGDA TUŠEK-ŽNIDARIČ3, OLGA GRACH- POGREBINSKY2, TINA ELERŠEK1, MONIKA CECILIJA ŽUŽEK4, ANJA BUBIK1 AND ROBERT FRANGEŽ4

The aim of this study was to detect cyanobacterial cytoskeletal elements and the cytoskeletal framework using immunostaining with anti-bovine a-tubulin mouse monoclonal antibodies. After strong permeabilization of axenic cyanobacterial cell lines, the cytoskeleton elements become visible in all cells. A mild cell permeabilization procedure allows the discrimination between healthy and senescent or otherwise stressed cyanobacteria whose cell integrity has been jeopardized. This technique can be useful to investigate cyanobacterial bloom lysis provoked by various natural or artificial factors. Viruses, among others, are important mortality agents of cyanobacteria. The presence of non-hepatotoxic cyclic cyanopeptides can provoke lysis of non-axenic Microcystis aeruginosa cell lines. This is presumably due to lytic cycle induction in lysogen cyanobacteria. A susceptible cyanobacterial cell line exposed to the depsipeptide planktopeptin BL1125 has been analysed with transmission electron microscopy to corroborate the involvement of virus like particles (VLP) in the process of lysis. VLP that correspond in shape and size to tailed cyanophages have been observed only in samples where the process of lysis has been triggered. The immunostaining of cytoskeletal elements by using epifluorescence and confocal microscopy has confirmed that the lysis expands from single infected cells or cell groups, the focal points, to their immediate environment. Our in vitro experiments demonstrate that lysogen focal point formation, which follows induction by endogenous cyanobacterial cyclic peptides, could constitute, also in the natural environment, the basis for an extremely rapid and extensive cyanobacterial bloom collapse.