Biochemical stimulation of microalgae for enhancing biomass productivity

Abstract

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 (TDZ; 0.22 ppm), humic acid (HA; 20 ppm), kelp extract (KE; 250 ppm), methanol (MeOH; 500 ppm), ferric chloride (FeCl3; 3.2 ppm), putrescine (PU; 0.09 ppm), spermidine (SPD; 1.5 ppm) were prescreened for their influence on growth and metabolites for the green alga- Chlorella sorokiniana. C. sorokiniana responded best to phytohormones in the auxin family, particularly NAA. Combinations of phytohormones were studied which compared blends from within the auxin family as well as against other families. The following study investigated the impact on biomass and chlorophyll productivity by comparing the delivery method of one of the top performing compounds shortlisted from prior research, the synthetic auxin naphthalene acetic-acid (NAA), solubilized by ethanol or methanol. This treatment was applied to on the green alga, Chlorella sorokiniana, as well as a mixed consortium that includes C. sorokiniana along with two other wild-isolated green algae, Scenedesmus bijuga and Chlorella minutissima. It was found that the use of ethanol to dissolve NAA was the most effective to boost the biomass productivity of C. sorokiniana, whereas, the mixed consortia did not demonstrate a dramatic beneficial response. The most effective treatment, EtOH500ppm+NAA5ppm, along with two other NAA concentrations (NAA2.5ppm and NAA5ppm) were then applied to six diverse species of microalgae to determine if the treatment dosage was effective for other freshwater and marine green algae, cyanobacteria, coccolithophore and diatoms. The use of ethanol and NAA at a combined dosage of EtOH500ppm+NAA5ppm was found to generate the highest biomass productivity for each of the species which responded positively to the treatments. If scalable, NAA and ethanol may have the potential to lower production costs by increasing biomass yields for commercial microalgae cultivation.