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.