Unexpected silicon localization in calcium carbonate exoskeleton of cultured and fossil coccolithophores

Coccolithophores, marine calcifying phytoplankton, are important primary producers impacting the global carbon cycle at different timescales. Their biomineral structures, the calcite containing coccoliths, are among the most elaborate hard parts of any organism. Understanding the morphogenesis of coccoliths is not only relevant in the context of coccolithophore eco-physiology but will also inform biomineralization and crystal design research more generally. The recent discovery of a silicon (Si) requirement for crystal shaping in some coccolithophores has opened up a new avenue of biomineralization research. In order to develop a mechanistic understanding of the role of Si, the presence and localization of this chemical element in coccoliths needs to be known. Here, we document for the first time the uneven Si distribution in Helicosphaera carteri coccoliths through three synchrotron-based techniques employing X-ray Fluorescence and Infrared Spectromicroscopy. The enrichment of Si in specific areas of the coccoliths point to a targeted role of this element in the coccolith formation. Our findings mark a key step in biomineralization research because it opens the door for a detailed mechanistic understanding of the role Si plays in shaping coccolith crystals.

Automated summary

Coccolithophores, marine calcifying phytoplankton, play a significant role in the global carbon cycle. Understanding their biomineral structures, especially coccoliths, is crucial for both coccolithophore eco-physiology and biomineralization research. The discovery of a silicon requirement in coccolithophores has opened up new avenues for studying biomineralization. This study reveals the uneven distribution of silicon in Helicosphaera carteri coccoliths, providing insights into the targeted role of silicon in coccolith formation and advancing our understanding of biomineralization.