Examining Phosphate Physiology in Coccolithophore Life Cycle Stages

Abstract

Despite the significance of coccolithophores for biogeochemical cycling, much of their ecology remains poorly understood. In particular, their elusive haplo-diplontic life cyclehas been given little attention in the literature. Yet, it significantly impacts the extent of coccolithophore calcification, their vertical and horizontal distribution in the ocean, and potentially their global success. The aim of this project is to establish physiological differences between the life cycle stages of the ecologically important coccolithophores Coccolithus braarudiiandCalcidiscus leptoporus in response to changes in the essential macronutrient phosphorus (P). Haploid coccolithophores are more commonly found in P-limited environments, raising the question which underlying mechanisms cause this variable distribution between life stages. An initial investigation of growth, photophysiology, calcification, and storage of polyphosphate under P-limited conditions will determine which parts of coccolithophore physiology are heavily impacted by P-limitation. An in silicoanalysis of P acquisition and transport genes in coccolithophores and other closely related eukaryotes will highlight differences in P physiology among these groups. Comparing proteins expressed in haploid and diploid coccolithophores under P-limitation will then be used to reveal whether P acquisition strategies differ between the two life stages. These results will further shed light on potential adaptations of haploid and diploid coccolithophores to different ecological niches. A profound understanding of coccolithophore physiology is vital to revealing their evolutionary success and their impact on ocean biogeochemistry and ecology.