Introduction of the Carotenoid Biosynthesis α-Branch Into sp. PCC 6803 for Lutein Production.

Lutein, made by the α-branch of the methyl-erythritol phosphate (MEP) pathway, is one of the most abundant xanthophylls in plants. It is involved in the structural stabilization of light-harvesting complexes, transfer of excitation energy to chlorophylls and photoprotection. In contrast, lutein and the α-branch of the MEP pathway are not present in cyanobacteria. In this study, we genetically engineered the cyanobacterium for the missing MEP α-branch resulting in lutein accumulation. A cassette comprising four genes coding for two lycopene cyclases ( and ) and two hydroxylases ( and ) was introduced into a strain that lacks the endogenous, cyanobacterial lycopene cyclase . The resulting strain showed wild-type growth and only moderate changes in total pigment composition under mixotrophic conditions, indicating that the deficiency can be complemented by lycopene cyclases leaving the endogenous β-branch intact. A combination of liquid chromatography, UV-Vis detection and mass spectrometry confirmed a low but distinct synthesis of lutein at rates of 4.8 ± 1.5 nmol per liter culture at OD (1.03 ± 0.47 mmol mol chlorophyll). In conclusion, provides a suitable platform to study the α-branch of the plastidic MEP pathway and other functions related to lutein in a cyanobacterial host system.