Functional metabolism pathways of significantly regulated genes in Nannochloropsis oceanica with various nitrogen/phosphorus nutrients for CO fixation.

To determine the optimal CO concentration for microalgal biomass cultivated with industrial flue gas and improve carbon fixation capacity and biomass production. Functional metabolism pathways of significantly regulated genes in Nannochloropsis oceanica (N. oceanica) with various nitrogen/phosphorus (N/P) nutrients for CO fixation were comprehensively clarified. At 100 % N/P nutrients, the optimum CO concentration was 70 % and the maximum biomass production of microalgae was 1.57 g/L. The optimum CO concentration was 50 % for N or P deficiency and 30 % for both N and P deficiency. The optimal combination of CO concentration and N/P nutrients caused significant up regulation of proteins related to photosynthesis and cellular respiration in the microalgae, enhancing photosynthetic electron transfer efficiency and carbon metabolism. Microalgal cells with P deficiency and optimal CO concentration expressed many phosphate transporter proteins to enhance P metabolism and N metabolism to maintain a high carbon fixation capacity. However, inappropriate combination of N/P nutrients and CO concentrations caused more errors in DNA replication and protein synthesis, generating more lysosomes and phagosomes. This inhibited carbon fixation and biomass production in the microalgae with increased cell apoptosis.