Investigating the ecological role of cell signaling in free-living marine heterotrophic protists

Graduation date: 2011Phagotrophic protists are major consumers of microbial biomass in aquatic ecosystems. However, biochemical mechanisms underlying prey recognition and phagocytosis by protists are not well understood. We investigated the potential roles of cell signaling mechanisms in chemosensory response to prey, and in capture of prey cells, by a marine ciliate (Uronema sp.) and a heterotrophic dinoflagellate (Oxyrrhis marina). Inhibition of protein kinase signal transduction caused a decrease in both chemosensory response and predation. Inhibition of G protein coupled receptor signaling pathways significantly decreased chemosensory response but had no effect on prey ingestion. Inhibitor compounds did not appear to affect general cell health, but had a targeted effect. In addition, upon finding rhodopsin in protein extracts from the plasma membrane of O. marina, an investigation into the photosensory behavior of O. marina was made. This organism has a positive phototactic response to moderate levels of white light and a wavelength-specific phototactic response. O. marina response to light was affected by culture conditions and feeding state. In the presence of blue light, phytoplankton emit red fluorescence; results indicate that in the presence of blue light, O. marina exhibited a positive phototactic response to a simulated "patch" of phytoplankton suggesting the use of the photoreceptor to detect the red phytoplankton fluorescence. These results support the idea that cell signaling pathways known in other eukaryotic organisms are involved in feeding behavior of free-living protists. As this field of study makes advances and more information relating to biochemical signaling in free-living protists becomes available, it will give researchers new tools and approaches in the study of feeding behavior in marine protists