Improved production of echinenone and canthaxanthin in transgenic Nostoc sp. PCC 7120 overexpressing a heterologous crtO gene from Nostoc flagelliforme

Echinenone and canthaxanthin are important carotenoid pigments with food and industrial applications. Biosynthesis of echinenone and/or canthaxanthin is catalyzed by β-carotene ketolase (CrtO), with β-carotene as the substrate. In this study, we generated transgenic Nostoc sp. PCC 7120 overexpressing a heterologous crtO gene from Nostoc flagelliforme and evaluated the productivity of both pigments. Normal (BG11 medium, 30 °C) and osmotic stress (BG11 medium supplemented with 0.4 M mannitol, 30 °C) conditions were used for cultivation. As compared to control strain, production of echinenone and canthaxanthin in transgenic strain were respectively increased by more than 16 % and 80 %, under either normal or osmotic stress conditions. Especially upon the stress condition, higher proportion of echinenone and canthaxanthin in total pigments was achieved, which should be beneficial for downstream separation and purification. In addition, transgenic strain showed drought tolerance and could revive from desiccation treatment after rewetting. Thus, this study provided technical clues for production of both pigments in engineered cyanobacteria as well as for cyanobacterial anhydrobiotic engineering.