Investigation of contact-based cues mediating food uptake in the marine tintinnid ciliate Favella sp.

Marine ciliates are important consumers of marine phytoplankton and represent a vital link in the food web. These unicellular grazers exhibit complex feeding behaviors and can be highly selective in their prey choices. Recently, Echevarria et al. (2016) showed that the marine tintinnid ciliate Favella sp. preferentially ingested natural dinoflagellate prey Heterocapsa triquetra over prey proxies (polystyrene beads), which appeared to be mediated by contact-based cues at the cytostome, the cell’s oral apparatus. In the present study, I investigated the nature of this contact-based recognition. I offered a variety of neoglycoprotein-coated 15 μm polystyrene microspheres alongside natural prey to Favella sp. and observed ingestion over 10-20 min. Although uncoated beads, or those coated with only the chemical linker or protein, were ingested at very low rates, beads coated with mannose and fructose were ingested as much as or more than natural prey. Beads coated with other sugars (fucose, galactose, methyl-mannopyranoside, lactose, mannitol, glucose, and sucrose) were ingested at intermediate rates. Furthermore, pre-incubation with 10-50 μM dissolved sugars could inhibit uptake of live prey in a specific manner. I examined the genome of Tetrahymena, a model ciliate, for potential sugar-binding cell surface proteins and found a number of potential candidates. These results suggest that ciliates may employ sugar-binding proteins as part of their mechanism for prey recognition, similar to many other organisms. Prey selection likely depends on other surface molecules such as proteins, and my results also suggest an explanation for the paradoxical observation that additions of dissolved small side-chain amino acids can inhibit feeding by Favella and other marine grazers.