Melatonin and calcium act synergistically to enhance the coproduction of astaxanthin and lipids in Haematococcus pluvialis under nitrogen deficiency and high light conditions.

This study focused on the influence of integrating melatonin (MT) and calcium (Ca) on the simultaneous accumulation of astaxanthin and lipids in Haematococcus pluvialis under abiotic stress conditions. Compared with the control condition, MT induction enhanced astaxanthin and lipid contents by 65.89% and 27.38%, respectively. The highest contents of astaxanthin and lipids under combined exposure to MT and Ca were 3.8% and 49.53%, respectively, which were 1.13- and 1.21-fold higher than those of cells treated with MT alone. The application of MT and Ca also promoted the expression of carotenogenic and lipogenic genes and increased the levels of Ca and γ-aminobutyric acid (GABA) but decreased reactive oxygen species (ROS) levels. Further evidence indicated that the increased cellular Ca could promote astaxanthin biosynthesis under MT induction by regulating carotenogenic gene levels and GABA and ROS signalling. The integrated strategy efficiently improved the coproduction of astaxanthin and lipids in H. pluvialis.