Effect of environmental parameters on growth and calcification in marine coccolithophore Gephyrocapsa huxleyi CCMP371.

The coccolithophore Gephyrocapsa huxleyi is a major producer of CaCO3 in the world's oceans due to its production of coccoliths. Its domesticated cultivation may serve as a sustainable source of biogenic CaCO3 for several industrial applications. Intraspecific variation within G. huxleyi is well recognized, leading to varied physiological responses to environmental drivers. This study optimized the net production of coccoliths in a calcifying strain of G. huxleyi, CCMP371, by serially exploring the impacts of salinity, media nutrient concentration, light intensity, and temperature on growth and CaCO3 production. The strain grew well at high salinities (35-45 ppt), at temperatures between 22 and 26 °C, and required vitamin B12 for growth. Nutrient concentrations between L1/4 and L1/12 were optimal for both growth and calcification, with cultures growing to a maximum cell density of 1.9 x 106 cells mL-1 and with ∼75% CaCO3 biomass content. Adjusting photon flux density between 100-800 µmol m-2 s-1 through the growth curve yielded high-density cultures with a biomass productivity of 0.54 g L-1 day-1 and ∼85% CaCO3 biomass content at the 100 L scale. Photoperiod affected calcification, with cultures subjected to a dark cycle showing a 12% reduction in CaCO3 content. Under optimized conditions, final cell densities tripled and CaCO3 content in dry biomass increased by 30%. This study provides valuable insights into understanding the culture conditions necessary for enhancing growth and calcification in G. huxleyi for potential industrial production of biogenic CaCO3 and provides a methodology for future optimization experiments with coccolithophores.