초록
Astaxanthin is the most powerful antioxidant of all carotenoids and has great commercial value for use in the aquacultural, pharmaceutical, and food industries. The marine bacterium Paracoccus sp. strain N-81106 is one of the natural producers of astaxanthin, but its astaxanthin productivity is too low for economically feasible industrial production. We tried to improve the productivity of astaxanthin by this strain by a combination of (i) random mutagenesis and (ii) gene cloning/overexpression of astaxanthin-biosynthetic genes. In the first step, we isolated astaxanthin-overproducing mutants after random mutagenesis of strain N-81106. The mutants isolated, NG5 and NG9, showed greater production of astaxanthin than did the wild-type strain N-81106. The yield of astaxanthin in the mutants was about 17 times that in strain N-81106. In the second step, we cloned the astaxanthin-biosynthesis genes of strain N-81106 in Escherichia coli by using a broad-host-range vector, and we then mobilized the cloned genes from E. coli to strains N-81106, NG5, and NG9. The recombinant NG5 produced astaxanthin at 58mg/l-56 times the production of the original strain. The yield was further increased by fed-batch fermentation to reach 480mg/l culture fluid.