Low-dose copper and blue light increases the yield of value-added biomolecules in Kirchneriella contorta (Chlorophyceae)

Microalgae are a natural source of valuable compounds with a wide range of applications. Given their physiological plasticity, strategies aiming at increasing the content of biomolecules have been proposed. In this study, low-dose copper and blue/red lights were combined and used as a manipulative strategy to induce biomolecule accumulation in Kirchneriella contorta . Cultures were exposed to a 1.6 × 10 –9 to 1.7 × 10 –8 mol L −1 free copper (Cu 2+ ) concentration range under white light for 48 h. Afterwards, the white light was replaced with blue or red lights for up to 96 h. We evaluated population growth through growth rates, photosynthesis through pulse amplitude modulated fluorescence (PAM) and biomolecules by quantifying chlorophyll a , carotenoids, carbohydrates and proteins. The results showed that at 3.8 × 10 –9 mol L −1 Cu 2+ and blue light, 2 × more carotenoids, 4 × more carbohydrates and 3 × more proteins were accumulated in the cells compared to the control. Among the light colors, the blue light most significantly interfered with the algal metabolism compared to the other colors. Although growth rates and maximum and operational quantum yields were not affected, non-photochemical quenching (NPQ) increased under blue light, showing that its higher energy compared to red and white lights may have impacted the photosynthetic apparatus. This study contributes to the biotechnology of microalgae by proposing a manipulative strategy that triggered the build-up of biomolecules in K. contorta.