• astaxanthin;
  • Chlorella zofingiensis;
  • gene expression;
  • lutein;
  • lycopene β-cyclase

The isolation, characterization, and regulation by light and nitrogen of the lycopene β-cyclase gene from Chlorella zofingiensis Dönz (CzlcyB), involved in the biosynthesis of astaxanthin and lutein, have been performed in this work. These carotenoids are of high commercial value as dyes in food and as nutraceuticals. The open reading frame (ORF) of CzlcyB encoded a polypeptide of 546 amino acids. A single copy of CzlcyB has been found in C. zofingiensis. The chararacteristic Rossmann or dinucleotide binding fold, present in most lycopene cyclases, has been also identified in the LCYb of C. zofingiensis (CzLCYb). Heterologous genetic complementation in Escherichia coli showed the ability of the predicted protein to cycle both lycopene and δ-carotene. Phylogenetic analysis has shown that the deduced protein forms a cluster with the rest of the lycopene β-cyclases (LCYb) of the chlorophycean microalgae studied, being very closely related to LCYb of plants. Transcript levels of CzlcyB were increased under nitrogen deprivation, but no increase was observed under high-light conditions. However, high irradiance triggered astaxanthin synthesis, while nitrogen deprivation by itself could not induce it. The combination of high irradiance and nitrogen deprivation led to a significant enhancement of the astaxathin accumulation.