Astaxanthin is a carotenoid pigment abundant in the animal kingdom, e. g., red color appearing in salmons, porgies and shrimps is attributed to this pigment. But, the genes or enzymes mediating the biosynthesis of astaxanthin are unknown. This is because the late step enzymes in carotenoid biosynthesis are membrane-integrated proteins, which readily lose activity on solubilization, thus hampering their purification and subsequent cloning of the genes coding for them. We cloned the astaxanthin biosynthesis genes from a marine bacterium Agrobacterium aurantiacum by their functional expression in Escherichia coli carrying the Erwinia carotenogenic genes for the biosynthesis of lycopene or β-carotene. The region needed for astaxanthin synthesis is located on a 5.4kb BamHI fragments in the lycopene-producing E. coli. Its nucleotide sequencing showed there were five carotenogenic genes. The biosynthetic pathway from β-carotene to astaxanthin was elucidated for the first time at the level of the biosynthesis genes by chemical analysis of the pigments synthesized in the β-carotene or zeaxanthin-producing E. coli carrying the various combination of the A. aurantiacum carotenogenic genes.
