Proteomics: A novel approach to the study of prey recognition by planktonic protists.

Single-celled grazers (protists) form a key trophic link between organisms at the base of the marine food web (bacteria & phytoplankton) and larger planktonic predators (zooplankton). Many of these minute protist grazers can be considered fussy feeders, preferring certain prey items over others. Through selective feeding, they play a highly significant role in shaping the composition of their prey communities. Because of their sheer abundance within the oceans, these organisms effect how key elements, such as carbon and nitrogen, are cycled on a global scale. There is much evidence to suggest that protists can discriminate between similar-sized prey items based on differences in cell surface chemical composition of their prey. Within our previous grants, we have identified a receptor used by one protist species to recognise specific molecules present on the surface of its prey. Although this research provided a significant first step in understanding the mechanisms involved in prey recognition, given that different prey types possess different surface coatings, it is likely that cell recognition by single-celled predators involves more than one type of receptor. Within this grant, we will study all cell surface proteins expressed by a species of protist predator using a technique called proteomics. We will investigate how predator protein expression changes with different prey types. We will also determine which of the cell surface proteins bind to the prey and hence may be involved in prey recognition and selection. Our work will provide an important basis for understanding cell-to-cell interactions in aquatic environments, and lead to future studies on a wide range of plankton species, thus aiding our overall understanding of food webs and nutrient cycling within the ocean.