Biosynthesis of novel carotenoids
A number of carotenogenic genes have been cloned from Rhodobacter and Erwinia and are expressed in E. coli, permitting recombinant biosynthesis of not only different cyclic and acyclic carotenoids and oxo-carotenoids but also novel carotenoids. In E. coli, no carotenoid synthesis takes place. Therefore, its terpenoid pathways has been utilized and the genes for geranyl geranyl diphosphate (GGDP) synthase (crtB) and phytoene synthase (crtE) are inserted for the production of C₄₀ carotenoid phytoene. Subsequent desaturation by phytoene desaturase (encoded by crtI) and further modifications catalysed by a variety of enzymes (e.g. cyclases, hydroxylases, ketolases, etc.) result in the production of different carotenoids.