A strategy to promote carotenoids production in Dunaliella bardawil by melatonin combined with photoinduction.

Microalgae are considered to be a very promising class of raw material for carotenoid production. In this study, melatonin (MLT), a widely used plant growth regulator, was added to the autotrophic medium of Dunaliella bardawil to explore its effects on the growth and pigment accumulation of Dunaliella bardawil. The results showed that the induction of exogenous MLT alone was not beneficial to the growth and pigment accumulation of Dunaliella bardawil, and the higher the concentration, the more obvious the inhibitory effect on the algal cells. Therefore, a strategy to promote carotenoid accumulation in Dunaliella bardawil by combining exogenous MLT and light induction was carried out. Under 4500 LUX light intensity, the content of zeaxanthin was significantly increased under exogenous MLT induction. In the 200 μg/mL, 300 μg/mL, and 400 μg/mL MLT-treated groups, the zeaxanthin single-cell content in the 300 μg/mL-treated group was as high as 0.38 ng/mL (0.17 ng/mL in the control group), which was 1.24-fold higher compared to the control. Under 9500 LUX light intensity, all carotenoids showed an increasing trend in all experimental groups, except for zeaxanthin, which showed a decreasing trend. The effect of 300 μg/mL showed the most obvious in the 200 μg/mL,300 μg/mL, and 400 μg/mL MLT treatment groups, where the lutein, α-carotene and β-carotene contents were 1.24, 1.14 and 1.31 times higher than those of the control group, respectively. Overall, exogenous MLT at high light intensities had a significant effect on pigment accumulation in Dunaliella bardawil.