UC San Diego

Emiliania huxleyi Hay et Mohler is the most abundant coccolithophore in the world's oceans. In can be found in open ocean and coastal environments at all latitudes except polar, and it is able to form large blooms. This dissertation investigates proteins in E. huxleyi that are present on the cell surface under different conditions of nutrient limitation. Chapter I describes the importance of E. huxleyi as a widespread phytoplankter, as well as what is presently known about response to nutrient limitation. In Chapter II a nitrogen-regulated cell-surface protein is characterized on a molecular and biochemical level. Evidence suggests that this protein is a cell-surface amidase with specificity for glutamine and formamide. This protein was successfully expressed in a prokaryotic system to attempt to confirm its function. Chapter III describes the process of using a polyclonal antibody developed to this nitrogen-regulated protein to confirm its cell- surface localization on nitrogen-limited cells of multiple strains of E. huxleyi. This antibody is also used to show the presence of this cell-surface protein in environmental samples from a bloom of E. huxleyi in June of 1997. In Chapter IV, PCR-based, biochemical, and bioinformatic methods are used to molecularly characterize a phosphorus- regulated cell-surface protein. Finally, Chapter V synthesizes this work and suggests future directions