Astaxanthin production and expression of carotenogenic genes in a hyperproducing mutant of Xanthophyllomyces dendrorhous

Astaxanthin is produced by Xanthophyllomyces dendrorhous as its principle carotenoid but the production in the wild type strain is relatively low. A stable astaxanthin-hyperproducing strain, M34, was obtained in our previous work from N-methyl-N'-nitro-N-nitrosoguanidin mutagenesis. In this study the wild type and M34 strains were compared in terms of growth and carotenoid production. The expression levels and nucleotide sequences of carotenogenic genes idi, crtE, crtYB, crtI, crtR and crtS of both strains were studied by real-time polymerase chain reaction and polymerase chain reaction respectively. Gene expression results indicated that both crtE and crtS genes showed significantly higher expressions relative to the wild type throughout the production cycle, the highest being 1.3-fold and 3.8-fold respectively. The six carotenogenic genes exhibited a total of 38 nucleotide changes after mutation, including a missense mutation in idi gene (glutamic acid -> alanine) and crtI gene (histidine -> glutamine), and two missense mutations in crtE (lysine -> arginine; serine -> aspartic acid) and crtR genes (serine -> valine; glutamine -> proline).