BIOSYNTHESIS OF KETOCAROTENOIDS IN TRANSGENIC CYANOBACTERIA EXPRESSING THE ALGAL GENE FOR BETA-C-4-OXYGENASE, CRTO

The ketocarotenoid astaxanthin is produced by a number of marine bacte ria and microalgae. It is synthesized from beta-carotene by the additi on of two keto groups to carbons C4 and C4' and two hydroxyl groups to C3 and C3'. The gene, crtO, encoding beta-C-4-oxygenase which convert s beta-carotene to canthaxanthin was cloned from the green alga Haemat ococcus pluvialis. We transferred crtO to the cyanobacterium Synechoco ccus PCC7942, which contains a beta-carotene hydroxylase gene and norm ally accumulates beta-carotene and zeaxanthin. The genetically enginee red cyanobacterium produced astaxanthin as well as other ketocarotenoi ds. The results confirm that crtO can function in cyanobacteria in con junction with the intrinsic carotenoid enzymes to produce astaxanthin. Specifically, this finding indicates that beta-carotene hydroxylase, which normally converts beta-carotene to zeaxanthin, can also function in the biosynthesis of astaxanthin. These results provide the first e vidence of genetic manipulation of a plant-type carotenoid biosynthesi s pathway toward the production of novel carotenoids. (C) 1997 Federat ion of European Biochemical Societies.