Effects of nitrogen sources and levels on the growth and accumulation of lipids and arachidonic acid of three coccoid green algae

Abstract:

[Background] Lobosphaera incisa Reisigl is a unicellular coccoid green algae, one of the richest plant source of arachidonic acid (AA). However, its taxonomic position has been unclear so far. [Objective] The taxonomy of three coccoid green algae (SAG2468, SAG2043 and H4301) with similar morphology were clarified, and the effects of different nitrogen sources (NaNO3, (NH2)2CO, NH4HCO3, (NH4)2CO3, NH4NO3, (NH4)2SO4 and NH4Cl) and levels (18 mmol/L, 3 mmol/L) on their lipids and AA accumulation were analysed. [Methods] Molecular and morphology identification were used to analyse the taxonomic position of the three strains; dry weight, gravimeter and gas chromatographic analyses were used to determine the biomass concentration and the content of total lipids (TLs) and AA. [Results] The three strains all belonged to the genus of Lobosphaera. Parietochloris incisa SAG2468 was revised to Lobosphaera incisa; SAG2468 and H4301 were the different geographical strains of L. incisa. Myrmecia bisecta SAG2043 was revised to Lobosphaera bisecta. The high (18 mmol/L) and low (3 mmol/L) nitrogen concentration of NaNO3 and (NH2)2CO were all suitable for the growth of these three strains. Ammonium as nitrogen source inhibited the growth of algae, and the higher the concentration, the more inhibition. Low-nitrogen concentration could promote TLs and AA accumulation in all strains significantly (P<0.05). The remarkable TLs and AA volumetric productivities of 142.15 mg/(L·d) and 35.51 mg/(L·d) were obtained in SAG2043 at 3 mmol/L NaNO3, significantly higher than those of H4301 and SAG2468 (P<0.05). Under these conditions, the corresponding biomass concentration was 4.9 g/L, the TLs reached 43.49% and the AA contents were up to 10.86% of dry weight and 31.75% of the total fatty acids in SAG2043. [Conclusion] SAG2043 showed a more prominent advantage to AA production.