Picoplankton feeding by the ciliate Vorticella similis in comparison to other peritrichs emphasizes their significance in the water purification process

We measured the feeding and growth rates of sessile peritrich ciliate Vorticella similis on seven picocyanobacterial strains their accompanying bacterial flora in microcosm experiments. This several closely related species are important indicators activated sludge water treatment plants contribute significantly to purification process. The picocyanobacteria were isolated from oligo-mesotrophic subalpine lakes Austria, central Europe, represent different pigment types (phycoerythrin-rich, PE, phycocyanin-rich, PC) phylogenetic clusters. In contrast most previous studies with ciliates, we calculated grazing V. relatively long-term incubations (48 h). Ingestion clearance rate disappearance (ROD) prey experimental containers relative controls without ciliates. results confirmed hypothesis that is an indiscriminative suspension feeder would not select for features other than cell size. Ciliate ingestion depended picoplankton abundance biomass, but type functional response ciliates awaits further study. particular, it needs be tested if activity declines strongly at moderate low food levels. ROD method combined precise assessment abundances by flow cytometry used yielded moderately higher estimates as short-term experiments using fluorescently labeled prey. obtained highest values thus far reported Clearance also high comparable those two species. Our can quantify tremendous significance