The effect of potentially toxic cyanobacteria on ciliates (Ciliophora)

The most frequently observed cyanotoxins are microcystins. They trigger a cascade of events leading to cellular responses. The hypothesis of the study was that cyanobacteria affect ciliates as solitary species and as assemblages. The aim of our study was to determine whether ciliates respond to cyanobacteria because of the presence of cyanotoxins (microcystins—MC). We set up experiments with toxic ( Planktothrix agardhii and Microcystis aeruginosa ) and non-toxic ( Aphanizomenon flos - aquae ) cyanobacteria, solitary Spirostomum sp. (Ciliophora), and a simple ciliate assemblage. Predicted values showed statistically significant increase during the solitary Spirostomum sp. abundance in the presence of toxic P. agardhii (MC total concentration in cells 323.9 µg/l) and M. aeruginosa (MC total concentration in cells 31.9 µg/l) but a decrease in the presence of non-toxic A. flos - aquae . The abundance of Spirostomum sp., being a component of ciliate assemblage, decreased significantly in the presence of all the three species of cyanobacteria due to competition from small-sized ciliate species that graze bacteria more effectively compared to large-cell-sized Spirostomum . We conclude that toxic cyanobacteria may affect ciliates in various ways, not necessarily because of production of toxins. As a consequence of the presence cyanotoxins, a cascading effect of passing carbon in the food web might be induced.