Coccoliths as Adsorptive Reservoirs

A defining characteristic of the cosmopolitan coccolithophore Emiliania huxleyi is its production of coccoliths, a nanopatterned biomineral that impacts the global carbon cycle and allows us to view these unicellular planktonic protists from Earth-observing satellites. Coccoliths are subcellularly produced within a vesicle and coated in diverse organic matter constituents. Fully mature coccoliths are extruded through the cell membrane and scaffolded to the cell surface forming the coccosphere. Coccolith morphology can vary within blooms, allowing for their grouping into various `morphotypes’, and likely resulting in variable coccolith morphotype-dependent ecosystem interactions. Our recent work demonstrated calcification as a deterrent of viral infection, a process that triggers a massive release of free coccoliths. The associated ecosystem impacts of free coccoliths and their function in host-virus interactions are not well understood. Our findings show that released coccoliths are highly adsorptive to both free viruses and host cells. We found that adsorption dynamics are not only morphotype-dependent, but are also driven by specific macromolecules within coccolith-associated organic matter. There was a 90% difference in adsorption across a range of coccolith morphotypes. General oxidation of coccolith-associated organic matter via hypochlorite treatment largely abolished adsorption. Targeted enzymatic digestion of specific macromolecules (protease, amylase, lipase) also resulted in variable reductions in adsorptive properties. These observations suggest that coccoliths interact with both cellular and colloidal organic matter, likely impacting host-virus encounter rates. Our findings highlight a previously unknown linkage between biomineral nanoarchitecture, adsorptive properties, and interactive ecological processes. They further contextualize the broader ecophysiological roles of calcification and their impact on the marine carbon cycle.