Identification and Feeding Characterization of (Protozoa, Ciliophora, Hypotrichia) Isolated from Outdoor Mass Culture of .

Herbivorous protistan grazers are ubiquitous and abundant in marine and temperate freshwater environments. However, little is known about the algivorous ciliates and their feeding habits in outdoor mass algal cultures. In this study, we report on one hypotrich ciliate, identified as , from the outdoor mass culture of in Arizona, USA. A long-term field survey revealed that this species often occurs in culture in spring and summer, and can graze very heavily on cells. By isolating cells and then observing them via light microscopy and electron microscopy, detailed information about the morphology, ultrastructure, excystment process, and feeding characteristics of the ciliate was obtained. Specifically, it seems that has a range of different strategies for excystment, and the sharp change in the ion concentration in the environment around the cyst results in osmotic shock, which likely facilitates the excystment. Feeding experiments revealed that preferred to graze on chlorophytes as well as the diatom and had no interaction with chrysophytes or cyanobacteria. Molecular phylogenetic analysis based on the SSU rRNA gene sequence indicated that both the genus and the species are non-monophyletic. The information obtained from this study will help advance our understanding of the biodiversity and ecological function of , and will also be very useful in the development of early warning systems and control measures for preventing or treating this contaminant in microalgal mass cultures.