Oxidative stress modulates astaxanthin synthesis in Haematococcus pluvialis

Astaxanthin, a carotenoid with potent antioxidant effects, is produced by the green alga Haematococcus pluvialis in response to stressful environmental conditions. During encystment several cellular shifts occur, such as the initiation of carotenogenesis and accumulation of reactive oxygen species (ROS) intracellularly. While the presence of ROS during encystment has been established, the effect of ROS on carotenogenesis directly is still primarily unknown. In this study, the relationship between astaxanthin accumulation and ROS production were quantified in H. pluvialis. Cellular astaxanthin and ROS concentrations were measured over 14 days in response to the application of environmental variable, redox-sensitive compound, and ROS-scavenger treatments. Application of both environmental and redox-sensitive treatments induced encystment and carotenogenesis. Initial astaxanthin production rates over days 0–4 were highest in the redox-sensitive variable group, with a subsequent rate peak at days 7–9 for environmental test groups. Cellular ROS concentrations similarly peaked over days 0–4 and 7–9 for redox-sensitive and environmental test groups, respectively. All treatment groups later showed significant decreases in ROS concentration by days 11–14. Furthermore, application of ROS-scavenger treatments induced germination and decreased carotenogenesis rates. By quantifying the relationship between astaxanthin and ROS, this work supports the role of ROS as a modulator of carotenogenesis in H. pluvialis and of astaxanthin as a protective mechanism against oxidative stress. Applications of this study can be further applied to design a more optimized technique of commercial astaxanthin production by combining traditional environmental stress conditions with oxidative stress-inducing factors, reducing natural astaxanthin production time requirements by over 10%.