Isolation of diverse amoebal grazers of freshwater cyanobacteria for the development of model systems to study predator–prey interactions

A common method for large-scale production of algal crops is growth in outdoor open-air ponds. While this approach is more cost-effective, outdoor open-air ponds are prone to contamination by competing algae, pathogens, and eukaryotic grazers, including ciliates, flagellates, and amoebae. To characterize grazers of cyanobacteria, or blue-green algae, we have performed enrichments and isolations from water samples obtained from environmental sites and from an experimental production pond. We obtained a set of amoebal isolates that show diversity in phylogeny, morphology, and locomotion. After examination of grazing on solid medium and in liquid medium, we found that some amoebal isolates can graze on a range of cyanobacterial species, while other amoebal isolates appear to have a more limited prey range. These prey ranges correlate with observed growth rates and cyst formation, suggesting differing growth and survival strategies for amoebae in the environment. Taken together, this work provides a glimpse into the range of natural amoebal predators of cyanobacteria and establishes model systems of predator–prey interactions. Further characterization of these systems will facilitate development of strategies for crop protection of open-air algal production ponds.