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Microalgae have characteristics similar to higher plants, and recent research has shown that phytohormones can influence the metabolic and physiological processes of microalgae. Utilizing phytohormones to adjust the production capacity of microalgae could improve their position in the industrial raw material supply chain, accelerate the transition to green and sustainable industry, and reduce carbon emissions. This study investigated the effects of six phytohormones, including 6-benzylaminopurine, ethephon, gibberellin, indole acetic acid, naphthalene acetic acid, and salicylic acid, on the growth and biochemical composition of Chlorella vulgaris 31(Cv-31) after 12 days of culturing. The results showed that there were significant variations in the effects of different concentrations and species of phytohormones on the growth and biochemical composition of Cv-31. Among the six phytohormones, 10 mg L− 1 GA was the most effective in promoting growth and pigment accumulation, while 7.5 mg L− 1 SA resulted in a 3.3-fold increase in lipid production compared to the control. However, the phytohormones did not play a significant role in protein accumulation, while ETH and GA were helpful in the accumulation of soluble sugars. This study provides a comprehensive understanding of the effects of phytohormones on the main components of Cv-31 and can serve as a reference for related research and production.

Mixotrophic cultivation using organic carbon sources has become increasingly important for large-scale production and application of microalgae, as it can overcome the current commercial bottleneck of low yield and high cost associated with photoautotrophic and heterotrophic cultivation. In this study, we investigated the effects of adding two acetates, sodium acetate (NaAc) and ammonium acetate (NH4Ac), at different concentrations (2, 4, 6, 8, 10 and 12 g L-1) on the biomass, biochemical components content (pigments, proteins, soluble sugars and lipids) and fatty acid composition of Chlorella vulgaris 31 (Cv-31) under mixotrophic cultures. Our results showed that the addition of NaAc significantly increased the biomass and lipid content of microalgae compared with NH4Ac, with 10 g L-1 NaAc having the best effect on the growth and lipid synthesis. Furthermore, only 2 and 4 g L-1 NaAc promoted the synthesis of pigments in algal cells, while all different concentrations of NH4Ac were inhibitory. In contrast to pigments, the effect of two acetates on protein synthesis was opposite, which was promoted by low concentrations of NH4Ac. Both acetates had a "low concentration promotion, high concentration inhibition" effect on the synthesis of soluble sugars. Moreover, the percentage of saturated fatty acids in the fatty acid profile increased with the amount of NaAc supplementation, while stearic acid and oleic acid appeared. Our findings suggest that regulating the type and concentration of acetate can improve the biomass and lipid yield of Cv-31 to promote the microalgal biomass production.

Microalgae have characteristics similar to higher plants, and recent research has shown that phytohormones can in uence the metabolic and physiological processes of microalgae. Utilizing phytohormones to adjust the production capacity of microalgae could improve their position in the industrial raw material supply chain, accelerate the transition to green and sustainable industry, and reduce carbon emissions. This study investigated the effects of six phytohormones, including 6benzylaminopurine, ethephon, gibberellin, indole acetic acid, naphthalene acetic acid, and salicylic acid, on the growth and biochemical composition of Chlorella vulgaris 31(Cv-31) after 12 days of culturing. The results showed that there were signi cant variations in the effects of different concentrations and species of phytohormones on the growth and biochemical composition of Cv-31. Among the six phytohormones, 10 mg L − 1 GA was the most effective in promoting growth and pigment accumulation, while 7.5 mg L − 1 SA resulted in a 3.3-fold increase in lipid production compared to the control. However, the phytohormones did not play a signi cant role in protein accumulation, while ETH and GA were helpful in the accumulation of soluble sugars. This study provides a comprehensive understanding of the effects of phytohormones on the main components of Cv-31 and can serve as a reference for related research and production.

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