3.5. Effects of Different Light Intensities on the Growth and Phycocyanin Content of FACHB-314
The effect of rGO-TiO2 nanoparticles on the growth ofFACHB-314 under different light intensities. The effects of high light intensity, medium light intensity, and low light intensity on the growth of FACHB-314 by rGO-TiO2 nanoparticles. Figure 9(a) shows that under the culture conditions of three light intensities, the largest dry cell weight is the control group cultured at 275 μmol/m2/s without adding nanoparticles, and the smallest dry cell weight is 55 μmol/m2FACHB-314 cultured with TiO2 nanoparticles and the control group cultured under TiO2 nanoparticles (high light intensity is 275 μmol/m2/s, medium light intensity is 165 μmol/m2/s, low light intensity is 55 μmol/m2/s). Figure 9(b) and Table 2 show that the content of phycocyanin in FACHB-314 decreased slightly with light intensity. This decrement indicates that A. platensis is more inclined to accumulate phycocyanin under low light intensity. A. platensis cultivated in culture medium with TiO2nanoparticles or A. platensis doped with rGO-TiO2nanoparticles, the phycocyanin content under low light intensity is higher than the accumulation under high light intensity.
The phycocyanin content was 77.5 mg/g, 75.1 mg/g, and 88.4 mg/g under high light intensity, medium light intensity, and low light intensity, respectively. Compared with the phycocyanin content under high light intensity, the phycocyanin content of FACHB-314 cultured with nanoparticles under low light intensity increased by 10.9 mg/g, an increase of 6.4%. Therefore, without adding nanoparticles,FACHB-314 under a low light intensity culture environment is more conducive to the accumulation of intracellular phycocyanin. Under the condition of light intensity of 55 μmol/m2/s, the highest phycocyanin content is FACHB-314 cultured with rGO-TiO2 nanoparticles, and the content value is 89.6 mg/g. Then, the FACHB-314 cultured in the control group had a phycocyanin content of 88.4 mg/g; the FACHB-314 cultured with TiO2 nanoparticles had a phycocyanin content of 69.7 mg/g. FACHB-314 cultured with rGO-TiO2nanoparticles increased by 1.4% compared to the FACHB-314cultured in the control group and increased by 28.6% compared to theFACHB-314 cultured with TiO2 nanoparticles. In terms of phycocyanin production, the largest yield was theFACHB-314 co-cultured with rGO-TiO2nanoparticles. Compared with the control group, the yield of phycocyanin increased by 10.6%, and compared with the FACHB-314 co-cultured with TiO2 nanoparticles, it increased by 34.2 %.
Figure 10 shows that under the condition of light intensity of 55 μmol/m2/s, the maximum dry cell weight of the control group is 1.14 g/L, and the dry cell weight yield is 0.113 g/L/d.FACHB-314 cultured with rGO-TiO2 nanoparticle has a maximum dry cell weight of 1.19 g/L and a dry cell weight yield of 0.119 g/L/d. Compared with the control group with the same light intensity, its dry cell weight and dry cell weight yield increased by 4.4% and 5.3%, respectively. Under the light intensity of 165 μmol/m2/s, the maximum dry cell weight of the control group was 1.73 g/L, and the dry cell weight yield was 0.186 g/L/d.FACHB-314 cultured with TiO2 nanoparticles has a maximum dry cell weight of 1.47 g/L and a dry cell weight yield of 0.154 g/L/d. The maximum dry cell weight of FACHB-314 cultured with rGO-TiO2 nanoparticles was 1.66 g/L, and the dry cell weight yield was 0.178 g/L/d. Compared with the experimental group added with TiO2 nanoparticles under the condition of light intensity of 165 μmol/m2/s, the dry cell weight and dry cell weight yield of FACHB-314 cultured with rGO-TiO2 nanoparticles increased by 12.9% and 15.6%, respectively. Under high light intensity, the maximum dry cell weight of the control group was 2.76 g/L, and the dry cell weight yield was 0.320 g/L/d. FACHB-314 cultured with TiO2 nanoparticles has a maximum dry cell weight of 2.26 g/L and a dry cell weight yield of 0.258 g/L/d. FACHB-314 cultured with rGO-TiO2nanoparticles has a maximum dry cell weight of 2.58 g/L and a dry cell weight yield of 0.298 g/L/d. In the experimental group added with TiO2 nanoparticles and spirulina cultured with rGO-TiO2 nanoparticles, the dry cell weight and dry cell weight yield increased by 14.2% and 16.0%, respectively.
The dry cell weight increased by 2.17 times as the light intensity increased from low to high value. It shows that high light intensity is more conducive to the growth of A. Platensis FACH-314. High light intensity is compared with low light intensity, Spirulina’s photosynthesis receives more photoelectrons per unit of time, which improves photosynthetic efficiency, so it accumulates more organic matter and promotes the growth of A. platensis FACH-314.
The results indicate that FACHB-314 co-cultured with rGO-TiO2 nanoparticles has higher phycocyanin content than the other two groups. It shows that in the existing culture experiments with different light intensities, the addition of rGO-TiO2 nanoparticles will promote the accumulation of phycocyanin in FACHB-314 , and the promotion effect is higher than that of the culture with TiO2 nanoparticles.