Abstract
Unicellular phytoplanktonic algae (coccolithophores) are among the most prolific producers of calcium carbonate on the planet, with a production of ∼1026 coccoliths per year. During their lith formation, coccolithophores mainly employ coccolith-associated polysaccharides (CAPs) for the regulation of crystal nucleation and growth. These macromolecules interact with the intracellular calcifying compartment (coccolith vesicle) through the charged carboxyl groups of their uronic acid residues. Here we report the isolation of CAPs from modern day coccolithophores and their prehistoric predecessors and we demonstrate that their uronic acid content (UAC) offers a species-specific signature. We also show that there is a correlation between the UAC of CAPs and the internal saturation state of the coccolith vesicle that, for most geologically abundant species, is inextricably linked to carbon availability. These findings suggest that the UAC of CAPs reports on the adaptation of coccolithogenesis to environmental changes and can be used for the estimation of past CO2 concentrations.
Highlights
Unicellular phytoplanktonic algae are among the most prolific producers of calcium carbonate on the planet, with a production of B1026 coccoliths per year
In order to probe the diversity of coccolith-associated polysaccharides (CAPs), we cultured four extant species of coccolithophores
The genus Gephyrocapsa first appeared in the late Pliocene (B3.5 Ma) and rose to dominance in the Early Pleistocene[16]
Summary
Unicellular phytoplanktonic algae (coccolithophores) are among the most prolific producers of calcium carbonate on the planet, with a production of B1026 coccoliths per year. These findings suggest that the UAC of CAPs reports on the adaptation of coccolithogenesis to environmental changes and can be used for the estimation of past CO2 concentrations Calcifying coccolithophores form their intricate calcite structures within Golgi-derived intracellular vesicles and under the strict control of several components, such as an insoluble organic baseplate and water-soluble acidic polysaccharides[1,2,3]. This saturation state, given an abundance in calcium, and in species with a weak or absent carbon concentrating mechanism, is linked to the availability of carbon in the extracellular environment In this multidisciplinary study, we aim to elucidate the role of CAPs in dictating the morphological variation of coccoliths in relation to their adaptive strategy to changing CO2 concentrations over the millennia. We were able to shed light on the adaptation of CAPs through time and to propose their potential use as a species/strain biomarker and, more importantly, as a potential tool for inferring past environmental change
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