Study of microalgal behaviour in continuous culture using photosynthetic rate curves: The case of chlorophyll and carotenoid production by Chlorella vulgaris

Chlorella vulgaris (C. vulgaris) is a green microalga of commercial importance as a valuable source of chlorophyll, carotenoids and other products. It is known that variations of light and nutrient availability prompt adaptation mechanisms to maximize photosynthesis and growth, but scant research has been conducted in continuous culture. This work approached the study of C. vulgaris grown in continuous culture under nitrogen and light limitation in terms of pigment content and photosynthetic activity. Results showed that light limitation increased the number and size of the photosynthetic apparatus, showing a maximum photosynthetic rate of 0.98 mgO₂ g⁻¹_biomass min⁻¹. Nitrogen limitation exerted a detrimental effect on biomass concentration and photosynthetic rate, but was more efficient in terms of oxygen evolved per unit mass of chlorophyll than the light-restricted culture. High levels of pigments were obtained in light limited conditions with 79.1 mg/g of total chlorophyll and 14.2 mg/g of carotenoids, being nearly two times higher than values reported in batch culture for C. vulgaris. Also, pigment productivity was about 6 times higher in this work. These are promising results that make the continuous production of pigments a profitable alternative to batch systems. Further research is advisable on the optimization of continuous culture parameters for pigment production.