STRUCTURE AND FUNCTIONAL-ANALYSIS OF A MARINE BACTERIAL CAROTENOID BIOSYNTHESIS GENE-CLUSTER AND ASTAXANTHIN BIOSYNTHETIC-PATHWAY PROPOSED AT THE GENE LEVEL

A carotenoid biosynthesis gene cluster for the production of astaxanth in was isolated from the marine bacterium, Agrobacterium aurantiacum. This cluster contained five carotenogenic genes with the same orientat ion, which were designated crtW, crtZ, crtY, crtI and crtB. The stop c odons of individual crt genes except for crtB overlapped the start cod ons of the following crt genes. Escherichia coli transformants carryin g the Erwinia uredovora carotenoid biosynthesis genes provide suitable substrates for carotenoid biosynthesis. The functions of the five crt genes of A. aurantiacum were determined through chromatographic and s pectroscopic analyses of the pigments accumulated in some E. coli tran sformants carrying various combinations of the E. uredovora and A. aur antiacum carotenogenic genes. As a result, the astaxanthin biosyntheti c pathway is proposed for the first time at the level of the biosynthe sis genes. The crtW and crtZ gene products, which mediated the oxygena tion reactions from beta-carotene to astaxanthin, were found to have l ow substrate specificity. This allowed the production of many presumed intermediates of astaxanthin, i.e., adonixanthin, phoenicoxanthin (ad onirubin), canthaxanthin, 3'-hydroxyechinenone, and 3-hydroxyechinenon e.