Effect of biochemical stimulants on biomass productivity and metabolite content of the microalga, Chlorella sorokiniana.

The influence of 12 biochemical stimulants, namely 2-phenylacetic acid (PAA; 30 ppm), indole-3 butyric acid (IBA; 10 ppm), 1-naphthaleneacetic acid (NAA; 2.5, 5 and 10 ppm ), gibberellic acid (GA3, 10 ppm), zeatin (ZT; 0.002 ppm), thidiazuron (0.22 ppm), humic acid (20 ppm), kelp extract (250 ppm), methanol (500 ppm), ferric chloride (3.2 ppm ), putrescine (0.09 ppm), spermidine (1.5 ppm) were prescreened for their impact on growth and chlorophyll for the green alga--Chlorella sorokiniana. C. sorokiniana responded best to phytohormones in the auxin family, particularly NAA. Thereafter, two studies were conducted on combinations of phytohormones to compare blends from within the auxin family as well as against other families. These treatments were NAA(₅ ppm)+PAA(₃₀ ppm), NAA(₂.₅ ppm)+PAA(₁₅ ppm), NAA(₅ ppm)+IBA(₁₀ ppm), NAA(₅ ppm)+GA3(₁₀ ppm), NAA(₅ ppm)+ZT(₁ ppm), and NAA(₅ ppm)+GA3(₁₀ ppm)+ZT(₁ ppm). Combinations of NAA with other auxins did not have synergistic or antagonistic effects on the growth. However, combinations of compounds from different phytohormone families, such as NAA(₅ ppm)+GA3(₁₀ ppm)+ZT(₁ ppm), dramatically increased the biomass productivity by 170% over the control followed by the treatments: NAA(₅ ppm)+GA3(₁₀ ppm) (138%), NAA(₅ ppm)+ZT(₁ ppm) (136%), and NAA(₅ ppm) ( 133%). The effect of biochemical stimulants were also measured on metabolites such as chlorophyll, protein, and lipids in C. sorokiniana. Renewed interest in microalgae for biotechnology and biofuel applications may warrant the use of biochemical stimulants for cost reduction in large-scale cultivation through increased biomass productivity.