Microalga Chlorella sorokiniana Response to Salinity: Effects on Cell Density, Size, and Pigment Accumulation

Microalgae, such as those from the genus Chlorella, produce biochemical compositions such as lipids, protein, and pigment. This research investigated the effects of different salinity levels in a nutrient medium on the growth and pigment synthesis of Chlorella sorokiniana. Microalga C. sorokiniana was cultured and grown in 500 mL glass bottle with varying concentrations of sodium chloride (10,15, 20, and 25 g L-1 NaCl) in a BG-11 medium, starting at an initial cell density of 2.68 x 105 cell mL-1. The cultures were maintained at 20 ± 1 °C, under continuous aeration, with a light intensity of 200 µmol photons m⁻² s⁻¹, a 24 h light photoperiod, and pH 7.5 ± 0.2. The results revealed that the optimal salinity concentration for enhancing the cell density, and the specific growth was 10 g L-1, demonstrating the highest cell density, exceeding the control group by 1.27-fold cell mL-1 at day 15 of the culture period. Additionally, the specific growth rate (SGR) was significantly higher in the 10 g L-1 of salinity concentration, achieving (0.05 ±0.14 day-1) as early as day 6 of the culture period compared to the other experimental groups. Cell size also increased significantly with 20 g L-1 of salinity concentration (49.91 ± 2.39 µm). Regarding the pigment accumulation, total carotenoid levels and chlorophyll-a, the elevated salinity concentration of 20 g L-1 suppresses chlorophyll-a accumulation and exhibited a reduction in total carotenoid pigment accumulation. Thus, these findings suggest that lower salinity levels (10 g L⁻¹ NaCl) can effectively enhance the growth of Chlorella sorokiniana, while higher salinity levels (20 g L⁻¹ NaCl) tend to suppress pigment production, particularly chlorophyll-a and total carotenoids accumulation.