Acute combination of nitrogen and light induces the simulta-neous accumulation of astaxanthin and lutein in continuous cultures of the microalga Chromochloris zofingiensis

The opposite was recorded for 9% N. Average irradiance positively affected lutein accumulation at both high and low nitrate, whereas that of astaxanthin did only increase under nitrogen-limiting conditions. An integrated analysis of transcriptomics and carotenoid profiling data provides evidence that the response to nitrogen is more significant than that to light availability, and that a synergy exists between both factors, with enhancement of their individual effects.

Regulation appears to be orchestrated at several levels: the expression pattern of cyclases suggests a redirection of lycopene to β-carotene, which is converted into astaxanthin through overexpression of BKT1. In turn, slightly higher lutein values are achieved by altering the α-carotene/lutein ratio, due to upregulation of CYP97A1 and CYP97C, especially under high irradiance conditions. The differential responses of astaxanthin and lutein to nitrogen and light availability could enable the programmed generation of C. zofingiensis biomass in continuous culture with a specific astaxanthin to lutein ratio, through careful adjustment of the nitrate concentration in the feed medium, using light irradiance as a modulator.