Abstract
Gloeobacter violaceus PCC 7421 is a unicellular cyanobacterium which is thought to be branched off at the earliest stage within the cyanobacterial clade by phylogenetic analysis based on the 16S rRNA sequences. Thus, Gloeobacter might retain traces of the ancestral properties of cyanobacterium. We analyzed carotenoid composition and identified carotenoid biosynthetic genes. The major carotenoid was β-carotene, and oscillol-di(L-fucoside) and echinenone were also identified. However, other carotenoids which exist among various cyanobacteria, were not detected. We searched for the carotenoid biosynthetic genes in the genome sequence of Gloeobacter. Whereas two plant-type desatulase genes (crtP and crtQ) that catalyze desaturation steps sequentially from phytoene to lycopene were not found, a bacterial-type phytoene desatulase (crtI) existed. In vivo functional complementation experiment revealed that CrtI produced lycopene by catalyzing 4-steps desaturation of phytoene. This is the first demonstration that oxygenic photosynthetic organism uses the bacterial-type phytoene desaturase.
