Naphthalene acetic acid and scorbic acid significantly improve neutral lipid accumulation in Chlorella species under nutrient limitations

Abstract

Nutrient starvation condition has already been exploited as a suitable strategy to induce more lipid production. In this study, nutrient limitation has been coupled with phytohormone or antioxidant supplementation to identify the potential of chemical stimulants to support growth and neutral lipid accumulation. Naphthalene acetic acid (NAA), and Ascorbic acid (AA), at concentrations of 5, 10, and 15 ppm were supplemented to N-limited level 1 (0.25 g NO3-N/L), N-limited level 2 (0.041 gNO3-N/L), and P-limited (0.01 gPO4-P/L) culture media of two Chlorella species to maximize biomass and lipid production. The results show that neutral lipid content increases 70 % when AA is added to the P-limited medium of Chlorella vulgaris IG-R-96 at 15 ppm. At N-limitation level 1 coupled with NAA and AA supplementations at 15 ppm, neutral lipid contents increase 107 % and 128 % in C. vulgaris IG-R-96, and 42 % and 60 % in Chlorella sorokiniana IG-W-96, respectively. When simultaneous N- and P-limitation is applied, neutral lipid content becomes almost double in C. vulgaris IG-R-96 at 10 ppm of NAA supplement. The effects of phytohormone and antioxidant on growth and neutral lipid accumulation is species-dependent and could be more effective when it is combined with nutrient limitation conditions. Stimulant supplementation is significantly effective for neutral lipid accumulation.