Biomineralization by marine phytoplankton, such as the silicifying diatoms and calcifying coccolithophores, plays an important role in carbon and nutrient cycling in the oceans. Silicification and calcification are distinct cellular processes with no known common mechanisms. It is thought that coccolithophores are able to outcompete diatoms in Si-depleted waters, which can contribute to the formation of coccolithophore blooms. Here we show that an expanded family of diatom-like silicon transporters (SITs) are present in both silicifying and calcifying haptophyte phytoplankton, including some globally important coccolithophores. Si is required for calcification in these coccolithophores, indicating that Si uptake contributes to the very different forms of biomineralization in diatoms and coccolithophores. Significantly, SITs and the requirement for Si are absent from highly abundant bloom-forming coccolithophores, such as Emiliania huxleyi. These very different requirements for Si in coccolithophores are likely to have major influence on their competitive interactions with diatoms and other siliceous phytoplankton.
Bibliographical noteFunding Information:
We thank Roy Moate, Glenn Harper and Peter Bond (University of Plymouth, UK) for help with electron microscopy imaging, Malcolm Woodward (Plymouth Marine Laboratory, UK) for help with silicate analyses, Nicholas Smirnoff and Hannah Florance (University of Exeter, UK) for help with protein sequencing and Nils Kroger and Nicole Poulsen (TU Dresden, Germany) for their guidance on analysing the organic component of the silica scales. This study was funded by EU Interreg IV Marinexus grant. GW and CB acknowledge support from NERC grant (NE/J021954/1). ART acknowledges NSF grant IOS 0949744 and the University of North Carolina Wilmington Microscopy Facility.