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Characterization of canthaxanthin biosynthesis genes from an uncultured marine bacterium.

Carotenoids are isoprenoid pigments synthesized in plants, fungi, bacteria and archaea, with roles in light harvesting, protection from stress, and membrane and protein structures. To characterize carotenoid biosynthesis genes from oceanic microbes, a fosmid library derived from microbial samples collected in surface water of the Pacific Ocean was screened in Escherichia coli for pigment-expressing recombinant strains. One DNA fragment enabled production of a bright orange pigment, and was analysed further by sequence analysis and phenotypic characterization. The cloned DNA encoded a five-gene cluster predicted to be involved in the synthesis of canthaxanthin, a ketolated carotenoid. Each of these genes was inactivated by insertion of a transposon, and the biochemical function of each gene product was confirmed. Sequencing of related fosmids generated a 67 kb genomic contig, and comparative analyses suggested that the DNA may originate from a deltaproteobacterium. The carotenoid biosynthesis genes described here are related to well-characterized families of carotenoid biosynthesis genes, but also indicate that the organism harbouring them is only distantly related to any previously characterized bacterial types.