Multiple promoters driving the expression of astaxanthin biosynthesis genes can enhance free-form astaxanthin production

Astaxanthin possesses various biological properties and is used in the animal and fish feed, food, and beverage industries. In this study, we derived zeaxanthin biosynthesis genes (crtE, crtB, crtI, crtY, and crtZ) from Erwinia uredovora and crtW from Agrobacterium aurantiacum. We fused inducible and constitutive promoters to astaxanthin biosynthesis genes to construct a novel plasmid (dubbed PTP3-6) that can effectively enhance free-form astaxanthin (FFAX) production. The PTP3-6 plasmid contains one T7 promoter, driving IPTG inducible crtW expression, and three constitutive promoters (isolated from E. uredovora) driving expression of the other zeaxanthin biosynthesis genes. Escherichia colt BL21 (DE3) cells carrying the PTP3-6 plasmid produced 8.3 mg/g dry cell weight astaxanthin, which is 69.4-fold higher than has been previously reported. Using multiple promoter fusions of astaxanthin biosynthesis genes could be applied in other hosts to enhance astaxanthin production. FFAX was identified in recombinant E. colt cells through ultra-performance liquid chromatography-mass spectrometry.