Comprehensive analysis of critical nutrient factors influencing the tropism of Nannochloropsis sp. for eicosapentaenoic acid-rich lipid production

Abstract

Nannochloropsis species are esteemed for their capacity to produce lipids rich in eicosapentaenoic acid (EPA), crucial for various industrial applications. However, elucidating the precise influence of critical nutrient factors on Nannochloropsis tropism poses challenges due to species-specific variations. This study aims to unravel the kinetic behavior of Nannochloropsis sp. CCAP 211/78 under varied critical nutrient concentrations and their combinatorial effects in both phototrophic and mixotrophic cultivation modes to enhance EPA-rich lipid production. The kinetic parameters for lipid production were maximized under optimal cultivation conditions of 45 g/L salinity, an N/P ratio of 25:1, and a nitrate concentration of 75 mg/L. Mixotrophic cultivation at 20 g/L glucose induced maximum lipid accumulation due to oxidative stress, achieving lipid contents of 20.76 ± 0.26 % and 51.92 ± 0.36 % dry biomass in the early and late stationary phases, respectively. Combinatorial analysis of the optimized nutrients in phototrophic (OP) and mixotrophic (OM) modes of cultivation demonstrated synergy in enhancing overall lipid productivity. OP mode exhibited biomass productivity, lipid and EPA content of 166.71 ± 4.82 mg L⁻¹ d⁻¹, 28.36 ± 0.89 % and 60.32 ± 6.35 mg g⁻¹ dry biomass, respectively, compared to 116.69 ± 2.24 mg L⁻¹ d⁻¹, 39.23 ± 1.45 % and 81.73 ± 8.38 mg g⁻¹ dry biomass, respectively, in OM mode. This research contributes to a comprehensive understanding of the interplay between critical nutrients and Nannochloropsis tropism, providing valuable insights for optimizing EPA-rich lipid production at different biorefinery scenarios.