Effect of distinct nitrate concentrations on pigment content of mixed culture of Chlorella vulgaris and Dunaliella sp.

Chlorella vulgaris and Dunaliella sp. are prominent microalgae that are generally used for natural pigment stocks. These species have been established as producer of valuable bio compounds such as chlorophyll, carotenoids, and astaxanthin. For this research, C. vulgaris and Dunaliella sp. were cultivated in mixed culture under nitrogen stress treatments. Total four treatments at distinct nitrate concentrations of 0.012, 0.025, 0.5 NaNO₃ g/L, respectively including nitrogen starvation was incorporated in this study. Nitrogen limitation and nitrogen starvation are widely used techniques to manipulate metabolic pathways into secondary pigments biosynthesis in microalgae cells. In addition, spectrophotometric measurement was conducted to investigate every single pigment content in all four treatments of distinct nitrogen concentrations for 14 days. The highest chlorophyll-a (23.65 mg/L), chlorophyll-b (10.02 mg/L), and total carotenoids (7.61 mg/L) were obtained from mixed culture with a concentration of 0.025 g/L NaNO₃ in the last period cultivation. Conversely, the highest content of astaxanthin (0.6 mg/L) in mixed culture of C. vulgaris and Dunaliella sp. in the last period cultivation was achieved from starvation of nitrogen as well. The microalgae demonstrated robust growth in the presence of diverse bacterial community in the culture. It is well known that microalgae are associated with the microbiota on its phycosphere biofilm. Yet, it is unclear which specific bacteria taxa have a role in supporting or inhibiting microalgae growth.