Biomass Accumulation and Physiological Characteristics of Chlorella pyrenoidosa with Different Forms of Organic Phosphorus under the Mixotrophic Mode

Microalgal cultivation with wastewater can recover nutrients and high value-added products. However, biomass accumulation and physiological responses of microalgae under different organic phosphorus (OP) forms have rarely been explored. In this study, the effects of three OP forms, including adenosine triphosphate (ATP), glucose-6-phosphate (G-6-P), and β-glycerol phosphate (β-GP), on the Chlorella pyrenoidosa growth, biochemical composition, morphological characteristic, photosynthesis, and cell viability under different concentrations were investigated. Results showed that except for the negative effect of 250 mg-P/L ATP, all OP forms contributed to microalgal growth, with the maximal algal density of 2.5 × 107 cells/mL under 250 mg-P/L β-GP. Particularly, 50 mg-P/L ATP and 250 mg-P/L phosphomonoesters (G-6-P and β-GP) could significantly promote carbohydrate, protein, and chlorophyll accumulation. Both low concentration ATP/β-GP and high concentration G-6-P were suitable for lipid production. Compared with microscopic imaging, flow cytometry quantitatively confirmed that 50 mg-P/L ATP expanded the cell size and destroyed cell membrane integrity, while 250 mg-P/L β-GP increased the proportion of low pigment cells. Increasing the OP concentration weakened the photosystem-II photochemical activity. Higher esterase activity with ATP addition showed enhanced cell viability. This result provides better guidance on directional enrichment of energy storage materials in microalgae with wastewater.