Harnessing coccolithophores for carbon capture and storage: exploring nutrient enrichment for future biotechnological applications

A less studied yet promising microalgal group within the field of Carbon Capture Usage and Storage (CCUS) is the calcifying marine microalgae known as coccolithophores. They could have significant potential for carbon capture since they can capture CO 2 , partitioning carbon into both their organic tissues and inorganic exoskeletons, composed of several micrometric plates of calcium carbonate (CaCO 3 ), called coccoliths. Moreover, the complex coccolith architecture offers valuable potential for nanotechnological applications, promoting also their reuse within a circular economy. However, comprehensive knowledge of their biotechnological potential and preliminary strain screening for quality assessment remain limited. In this study, a screening aimed at identifying the most promising strains for potential industrial applications was carried out by testing their response and yield under increasing nutrient and carbon supplies: dry weight (DW) and nutrient consumption efficiency were measured for the species Gephyrocapsa huxleyi (formerly Emiliania huxleyi ) and two strains of the species Chrysotila roscoffensis, to identify the most promising strain for industrial applications. We documented a positive effect of nutrient enrichment and an even stronger response to carbon supplementation in the form of sodium bicarbonate (NaHCO 3 ) on the growth of C. roscoffensis and on CaCO 3 production in G. huxleyi . One C. roscoffensis strain proved to be the most promising, exhibiting the highest DW (1,172.7 ± 42.2 mg/L) and CO 2 absorption (1,210.7 ± 3.1 mg/L) compared to G. huxleyi (569.4 ± 20.5 mg/L; 329.9 ± 11.9 mg/L), as well as a stable ratio between Particulate Inorganic Carbon (PIC) and Particulate Organic Carbon (POC) during cultivation. Our experiments also highlighted the ability of G. huxleyi to produce significant amounts of carbonate (2.1 ± 1.1 PIC:POC) compared with the less calcified C. roscoffensis (0.34 ± 0.01 PIC:POC) under enhanced carbon supply. This study emphasizes the importance of preliminary screening to identify the most suitable strain for industrial exploitation, particularly among understudied microalgae such as coccolithophores.